What are zoonotic diseases?

Definition

Domestic and wild animals, and their ecosystems, contribute to human health and well-being. Animals provide protein-rich nutrients, transportation, fuel, recreation, and companionship. With the many benefits people derive from animals (including arthropods) comes health risks at this human, animal, and ecosystem interface. This interface can be described as a continuum of direct or indirect human exposure to animals, their products, and their ecosystems.

Zoonotic diseases, also known as zoonoses, are diseases caused by infectious agents (viruses, bacteria, and parasites such as worms and protozoa) transmitted or shared by animals and humans. These diseases are caused by a diverse group of pathogenic microorganisms that ordinarily live among animals. Some zoonotic diseases are transmitted directly from animals to humans, some result from contamination of the environment by animals, and others require a vector, such as a tick or mosquito.

Viral Infections

Arthropod-borne viruses include any of a large group of ribonucleic acid (RNA) viruses that are transmitted primarily by arthropods. There are more than four hundred species of arboviruses. Zoonotic diseases caused by viruses include the following:

Encephalitis. Encephalitis is inflammation of the
brain caused by infection. All arboviral encephalitides are zoonotic. They are
maintained in complex life cycles involving a nonhuman primary vertebrate host and
a primary arthropod vector. Many arboviruses that cause encephalitis have a
variety of vertebrate hosts, and some are transmitted by more than one vector.

Four main flavivirus agents of encephalitis exist in the United States:
eastern equine
encephalitis, western equine encephalitis, St. Louis
encephalitis, and La Crosse encephalitis, all of which are transmitted by
mosquitoes. Most human infections are asymptomatic or may result in nonspecific
flulike symptoms. In some infected persons, infection may progress to full-blown
encephalitis, with permanent neurologic damage or even death. Because the
arboviral encephalitides are viral diseases, antibiotics
are not effective for treatment; no effective antiviral drugs have been developed.
There are no commercially available human vaccines for these diseases, so
treatment is supportive.

West Nile virus. West Nile virus (WNV) is a flavivirus
commonly found in Africa, West Asia, the Middle East, and the United States. The
virus can infect humans, birds, mosquitoes, horses, and other mammals. WNV was
first diagnosed in the United States in 1999.

Most human infections are asymptomatic or may result in a nonspecific flulike syndrome. Approximately 80 percent of people who are infected with WNV will not show any symptoms. Up to 20 percent of infected people develop swollen lymph glands or a skin rash on the chest, stomach, and back. About 1 in 150 infected persons will develop severe illness, with symptoms that can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, and muscle weakness.

There is no specific treatment for WNV infection. In milder cases, symptoms resolve on their own. In more severe cases, infected persons should seek supportive treatment in a hospital.

Hantavirus pulmonary syndrome. Hantavirus pulmonary syndrome
(HPS) is contracted from rodents and has been identified throughout the United
States. Rodent infestation in and around the home remains the primary risk factor
for hantavirus exposure. In the United States, deer mice, cotton
rats, rice rats, and white-footed mice carry hantaviruses that cause HPS.

Although rare, HPS is potentially deadly. Humans can contract the disease when they come into contact with infected rodents or their urine and droppings or when they breathe in the hantavirus from the air. HPS cannot be transmitted from one person to another.

Early symptoms include fatigue, fever, muscle aches, headaches, dizziness, chills, and abdominal problems. Four to ten days later, additional symptoms appear. These symptoms include coughing and shortness of breath, as the lungs fill with fluid. There is no specific treatment or vaccine for hantavirus infection. Supportive care is the basis for therapy.

Lymphocytic choriomeningitis. Lymphocytic choriomeningitis (LCM) is a rodent-borne viral disease that appears as aseptic
meningitis (inflammation of the membrane that surrounds the brain and spinal
cord), encephalitis, or meningoencephalitis (inflammation of the brain and
meninges). LCM is caused by the lymphocytic choriomeningitis virus (LCMV). The
common house mouse, Mus musculus, is the primary host. The virus
is found in the saliva, urine, and feces of infected mice, and people become
infected when exposed to these substances. Other types of rodents, such as
hamsters, can become infected with LCMV in pet stores.

Initial LCM symptoms include fever, malaise, lack of appetite, muscle aches,
headache, nausea, and vomiting. In the second phase of the infection, persons have
symptoms of meningitis (fever, headache, and stiff neck) or
characteristics of encephalitis (drowsiness, confusion, and sensory disturbances),
or have symptoms such as motor abnormalities (for example, paralysis). LCM is
usually not fatal. Aseptic meningitis, encephalitis, or meningoencephalitis
require hospitalization. Anti-inflammatory drugs, such as corticosteroids, may be helpful in treating the disease.

Monkeypox. Monkeypox is a rare viral disease that
usually occurs in central and western Africa. It is caused by the monkeypox virus,
which was first found in 1958 in laboratory monkeys. In June, 2003, several people
in the United States contracted monkeypox after having contact with pet prairie
dogs that were sick with monkeypox. The disease was traced to a shipment of
Gambian rats that were imported to the United States and later kept near prairie
dogs at an Illinois animal vendor.

People can get monkeypox if they are bitten by an infected animal or if they
touch the animal’s blood or body fluids. The disease also can spread from person
to person. After infection, symptoms include fever, headache, muscle aches,
backache, and swollen lymph nodes. A few days later, symptoms include a skin rash
that develops into raised bumps filled with fluid; these bumps will eventually
fall off the skin. The illness usually lasts two to four weeks. There is no
specific treatment for monkeypox.

Rabies. Rabies is a viral disease of mammals
transmitted through the bite of a rabid animal. Transmission is through the
virus-containing saliva of an infected host. The majority of rabies cases occur in
wild animals such as raccoons, skunks, bats, and foxes.

The rabies virus infects the central nervous system of humans, ultimately involving the brain and leading to death. Early symptoms include fever, headache, and general weakness. As the disease progresses, more specific symptoms appear, including insomnia, anxiety, confusion, partial paralysis, hallucinations, hypersalivation (increased saliva), difficulty swallowing, and hydrophobia (fear of water). Once clinical signs of rabies appear, the disease is nearly always fatal, and treatment is mainly supportive.

Several tests are required for the diagnosis of rabies. Thorough wound cleansing has been shown to markedly reduce the likelihood of contracting rabies. A tetanus shot should be given if the infected person has not received one within the previous ten years. A doctor will determine if antibiotics should be used. Persons not previously vaccinated should receive a postexposure vaccination against rabies that includes administration of both passive antibody and vaccine.

Bacterial Infections

Zoonotic diseases caused by bacterial infections include the
following:

Anthrax. Anthrax is an acute infectious disease
caused by the bacterium Bacillus anthracis. It most commonly
occurs in wild and domestic mammals such as cattle, sheep, and goats, but it also
can occur in humans who are exposed to infected animals or to tissue from infected
animals. B. anthracis spores can survive in the soil for many
years. Humans can become infected by handling products from infected animals or by
inhaling anthrax spores in contaminated animal products. Anthrax can also be
contracted by eating undercooked meat from infected animals.

Anthrax infections can be of three types: cutaneous (skin), inhalation, and gastrointestinal. Most cutaneous infections occur when the bacterium enters a cut or abrasion on the skin. About 20 percent of untreated cases of cutaneous anthrax result in death, but death is rare with antimicrobial therapy. The first symptoms of inhalation infection resemble a common cold, but after several days, the symptoms may progress to severe breathing problems. Inhalation anthrax is usually fatal. The gastrointestinal form of anthrax follows the eating of contaminated meat and is followed by an acute inflammation of the intestinal tract. Intestinal anthrax results in death in 25 to 60 percent of cases of infection. Antibiotics are used to treat all three types of anthrax. Early identification and treatment are critical.

Lyme disease. Lyme disease is caused by the bacterium
Borrelia burgdorferi and is transmitted to humans by the bite
of infected blacklegged ticks. The Lyme disease bacterium lives in deer, mice,
squirrels, and other small animals, and ticks become infected by feeding on these
animals. In the northeastern and north-central United States, Lyme disease is
transmitted by the deer tick Ixodes scapularis. In the Pacific
Northwest, the disease is spread by the Western blacklegged tick (I.
pacificus).

In approximately 70 to 80 percent of infected persons, the first sign of infection is usually a circular rash that appears three to thirty days after the tick bite. This “bull’s eye” rash gradually expands in several days, reaching up to twelve inches in diameter. Other early symptoms include fever, chills, headache, fatigue, swollen lymph nodes, and joint and muscle aches. If Lyme disease is left untreated, it can spread to other parts of the body. Symptoms of late-stage Lyme disease include painful, swollen joints; severe headaches and neck stiffness from meningitis; and nervous system problems, such as impaired concentration and memory loss.

Several laboratory tests for Lyme disease are available to measure
antibodies to the infection. These tests may return
false-negative results in persons with early disease, but they are reliable for
diagnosing later stages of disease. Most cases of Lyme disease can be treated and
cured with antibiotics.

Plague. Plague is an infectious disease of
animals and humans caused by the bacterium Yersinia pestis. It is
transmitted from animal to animal and from animal to human by the bites of
infected fleas. Humans usually contract plague from being bitten by a rodent flea
that is carrying the plague bacterium or by handling an infected animal. Plague is
also transmitted by inhaling infected droplets expelled by the coughing of an
infected person or animal, especially domestic cats, which may become infected by
eating infected wild rodents. Fleas become infected by feeding on rodents, such as
chipmunks, prairie dogs, ground squirrels, mice, and other mammals that are
infected with the bacterium. Fleas transmit the plague bacterium to humans and
other mammals during the feeding process.

The characteristic sign of plague is a very painful, swollen lymph node called
a bubo. This sign, accompanied with fever, extreme exhaustion, headache, and a
history of possible exposure to rodent fleas, should lead to suspicion of plague.
The disease progresses rapidly; the bacteria can then invade the bloodstream and
produce severe illness called plague septicemia and lung infection. Once a
human is infected, a progressive and potentially fatal illness generally results
unless specific antibiotic therapy is given. The plague vaccine is no longer
commercially available in the United States.

Rocky Mountain spotted fever. Rocky Mountain spotted
fever (RMSF) is the most severe tickborne illness in the
United States. It is caused by infection with the bacterial organism
Rickettsia rickettsii, which is transmitted by the bite of an
infected tick. The American dog tick (Dermacentor variabilis) and
Rocky Mountain wood tick (D. andersoni) are the primary arthropod
vectors in the United States.

The early symptoms of RMSF are often nonspecific. Initial symptoms may include
severe headache, lack of appetite, muscle pain, nausea, and fever. Later signs and
symptoms include diarrhea, joint pain, abdominal pain, and rash. RMSF can be a
severe illness, and the majority of infected persons are hospitalized. Diagnosis
is based on a combination of clinical signs and symptoms and laboratory tests. It
is best treated using a tetracycline antibiotic, usually
doxycycline.

Salmonellosis. Salmonellosis is an infection with the
bacterium Salmonella, which lives in the intestinal tracts of
humans, animals, and birds. Salmonella is usually transmitted to
humans through foods contaminated with animal feces. Contaminated foods are
usually of animal origin and include beef, poultry, milk, and eggs, but any food,
including vegetables, may become contaminated. Salmonella is
killed by thorough cooking. Salmonella may also be found in the
feces of some pets. Reptiles, such as turtles, lizards, and snakes, and chicks and
young birds, are particularly likely to carry Salmonella in their
feces. People should always wash their hands immediately after handling one of
these animals, even if it appears healthy. Most persons infected with
Salmonella develop diarrhea, fever, and abdominal cramps
twelve to seventy-two hours after infection. The illness usually lasts four to
seven days, and most persons recover without treatment.

Parasitic Infections

Zoonotic diseases caused by parasitic infections include the following:

Cryptosporidiosis. Cryptosporidiosis is a disease caused
by parasites of the genus Cryptosporidium. Both the disease and
the parasite are known as crypto. Many species of crypto infect humans and a wide
range of animals. The parasite is protected by an outer shell that allows it to
survive outside the body for long periods of time. Crypto is one of the most
frequent causes of waterborne disease among humans in the United States and
throughout the world. Crypto lives in the intestines of infected humans or
animals. An infected person or animal passes the parasites in the stool. Crypto is
found in soil, food, water, or surfaces that have been contaminated with the feces
from infected humans or animals. Some people with crypto have no symptoms, but the
most common symptom is watery diarrhea. Other symptoms include stomach cramps,
dehydration, diarrhea, nausea, fever, or weight loss. Diagnosis is made by
examination of stool samples. Most people who have healthy immune systems will
recover without treatment.

Cysticercosis. Cysticercosis is an infection caused by
the pork tapeworm Taenia solium. Infection occurs when the
tapeworm larvae enter the body and form cysticerci (cysts). When cysticerci are
found in the brain, the condition is called neurocysticercosis. The tapeworm that
causes cysticercosis is most often found in rural, developing countries where pigs
are allowed to roam freely and eat human feces.

When pigs swallow pork tapeworm eggs, the eggs are passed through the bowel
movement. The eggs are subsequently spread by people who ingest contaminated food
or water. Once inside the stomach, the tapeworm egg hatches, penetrates the
intestine, travels through the bloodstream, and may develop into larvae in the
muscles, brain, or eyes. Although rare, larvae may float in the eye and cause
swelling or detachment of the retina. Symptoms of neurocysticercosis can include
seizures, headaches, confusion, lack of attention, or difficulty with balance.
Death can occur suddenly with heavy infections.

Diagnosis is usually made by magnetic resonance imaging or computed
tomography brain scans. Infections are generally treated with antiparasitic drugs
in combination with anti-inflammatory drugs.

Trichinellosis. Trichinellosis, also called trichinosis,
is caused by eating the raw or undercooked meat of animals infected with the
larvae of a species of worm called Trichinella. Infection occurs
commonly in domestic pigs. When an animal eats meat that contains
Trichinella cysts (larvae), their stomach acid dissolves the
hard covering of the cyst and releases the worms. The worms migrate into the small
intestine and mature in one to two days. After mating, adult females lay eggs that
develop into immature worms and travel through the arteries to muscles. Inside the
muscles, the worms curl into a ball and become enclosed in a capsule. Infection in
humans occurs when these capsules are consumed in undercooked meat.

The first symptoms of trichinellosis include nausea, diarrhea, vomiting, fatigue, fever, and abdominal discomfort. These first symptoms are later followed by headaches, fevers, chills, cough, eye swelling, aching joints, muscle pains, itchy skin, or diarrhea. In severe cases, death can occur. For mild to moderate infections, most symptoms subside within a few months, although fatigue, weakness, and diarrhea may last for months afterward. Several effective prescription drugs are available to treat trichinellosis.

Impact

Zoonotic diseases have the potential to spread efficiently across international
boundaries, thereby affecting not only human health and well-being but also
international travel and trade. More than 60 percent of the newly identified
infectious agents that have affected people since the mid-twentieth century have
been caused by pathogens originating from animals or animal products. Of
these zoonotic infections, 70 percent originated from wildlife.

Bibliography

Hugh-Jones, Martin E., William T. Hubbert, and Harry V. Hagstad. Zoonoses: Recognition, Control, and Prevention. Ames: Iowa State University Press, 2000. Preceding synopses of parasitic, fungal, and viral agents are sections on the principles and history of zoonoses recognition, newer disease agents, and advances in control and prevention.

Krauss, Hartmut, et al. Zoonoses: Infectious Diseases Transmissible from Animals to Humans. 3d ed. Washington, D.C.: ASM Press, 2003. Discusses the myriad infections introduced by human-animal contact.

Mandell, Gerald L., John E. Bennett, and Raphael Dolin, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. New York: Churchill Livingstone/Elsevier, 2010. This thorough two-volume textbook provides comprehensive coverage of infectious diseases, including zoonotic diseases.

Romich, Janet A. Understanding Zoonotic Diseases. Clifton Park, N.Y.: Thomson Delmar, 2008. A good introduction to zoonotic diseases in humans.

Schlossberg, D., ed. Clinical Infectious Disease. New York: Cambridge University Press, 2008. A detailed presentation of infectious diseases, their causes, epidemiology, symptoms, and treatments.

What are measles?

Causes and Symptoms

Measles is a highly contagious viral disease characterized by a maculopapular (pimply) rash that develops on the skin and spreads rapidly over much of the cutaneous surface of the body. Measles virus is classified with the paramyxoviruses, a class of viruses in which ribonucleic acid (RNA) serves as the genetic material. Closely related viruses in the same group include rinderpest and distemper virus, agents associated with disease in ruminants such as cows and in dogs or cats, respectively. It is likely that measles originated when one of these other animal viruses became adapted to humans several thousand years ago.

In modern times but before the advent of measles vaccination, measles was a common disease of childhood, usually appearing between the ages of five and ten. The illness is among the most contagious of infections, and the virus was generally spread among children in schools. Widespread immunization of children, begun in the 1960s, tended to push the age of exposure into the teenage years. Most outbreaks since the 1980s have occurred among college students. Since recovery from the disease confers lifelong immunity, infection among older adults is infrequent. In developing nations, places where vaccination may be haphazard, measles is still a disease of early childhood; malnutrition and related problems of poverty have resulted in a significant level of mortality among infected children.

Exposure generally follows an oral-oral means of transmission, as the person inhales contaminated droplets from an infected individual. The incubation period for active measles ranges from seven to fourteen days. During this early stage, the infected individual becomes increasingly contagious. The lack of any obvious symptoms during these early stages lends itself to the spread of the disease.

Contact by the virus with the surface cells of the respiratory passages, or sometimes the conjunctiva (the outer surface of the eye), allows the infectious agent to enter the body. The virus spreads through the local lymph nodes into the blood, producing a primary viremia. During this period, the virus replicates both in the lymph nodes and in the respiratory sites through which the virus entered the body. The virus returns to the bloodstream, resulting in a secondary viremia and widespread passage of the virus throughout the body by the fifth to seventh day after the initial exposure. Viral levels in the blood reach their peak toward the end of the incubation period, some fourteen days after infection. Once symptoms begin, the virus is widely disseminated throughout the body, including sites in small blood vessels, lymph nodes, and even the central nervous system.

The initial incubation period is followed by a prodromal stage, in which active symptoms appear. This stage is characterized by a fever that may reach as high as 103 degrees Fahrenheit, coughing, sensitivity of the eyes to light (photophobia), and malaise. Koplik’s spots appear on the buccal mucosa in the mouth one to two days prior to development of the characteristic measles rash.

The maculopapular rash first appears on the head and behind the ears and gradually spreads over the rest of the body during the course of twenty-four to forty-eight hours. Clear signs of respiratory infection appear, including a cough, pharyngitis, and occasional involvement of the bronchioles or even pneumonia. While malaise and anorexia (appetite loss) are common during the fever period, diarrhea and vomiting generally do not occur. Over time, the rash becomes increasingly dense, exhibiting a blotchy character. Desquamation is common in many affected areas of the skin. Gradually, over a period of three to five days, the rash begins to fade, usually following the sequence by which it first appeared. The rash fades first on the forehead, then on the extremities.

Complications, while they do occur, are unusual in otherwise healthy individuals. Most result from secondary bacterial infections. Occasionally, these complications may manifest themselves as infections of the ear. Pulmonary infections are common among cases of measles and account for most of the rare deaths that follow development of the disease. Photophobia is also common, accounting for the former belief that measles patients had to be kept in a dark room; as long as the patient is comfortable, this step is unnecessary.

The obvious manifestations of measles infection make the isolation of the virus unnecessary for diagnosis. Ironically, the near disappearance of measles in the United States has made most physicians there unfamiliar with the disease; it is not unusual for an attending physician to mistake the rash for another illness. For this reason, laboratory diagnosis is often useful. Laboratory confirmation is generally based on a serological assay for measles antibodies in the blood of infected persons.

A rare sequela to measles infection is the development of subacute sclerosing panencephalitis, a disease characterized by progressive neurological deterioration. The specific mechanism by which measles infection may develop into this disease remains unclear, but it may be the result of a rare combination of events in the victim. Since spread of the virus into the central nervous system is common during measles infection whereas the development of subacute sclerosing panencephalitis is rare (approximately one case per one hundred thousand measles infections), it is likely that some form of immune impairment is at the root of this disease. Diagnosis of subacute sclerosing panencephalitis is difficult and is based on developing dementia accompanied by unusual levels of measles antibodies in cerebrospinal fluid.

Treatment and Therapy

No specific treatment for measles is available; therapy consists of symptomatic intervention. Bed rest is recommended, and the patient should not come into contact with persons not previously exposed to the virus through either natural infection or immunization.

Itching of the rash is common and may be treated with cool water or the standard regimen of cornstarch or baking soda applications. The most common complications result from secondary bacterial infections, which generally take the form of otitis media (middle-ear infection), pharyngitis, or pneumonia. Appropriate use of antibiotics is usually sufficient to prevent or treat such complications.

Immunization with the measles virus may be either passive or active. Children less than one year of age and patients who are immunocompromised or chronically ill may be protected if human immunoglobulin is administered within a week after exposure. While effective immunity is short term, it is capable of protecting these individuals during this period. Since no active disease or infection develops, however, immunity to future infection remains minimal in these cases.

During the early 1960s, an effective
vaccine was developed to immunize children against measles. The vaccine consists of an attenuated form of the virus. Although early forms of the vaccine were inconsistent in producing a lifelong immunity, they were effective in decreasing the prevalence of the disease. Later generations of the attenuated vaccine proved more effective in developing long-term immunity among the recipients.

Since maternal antibodies are present in newborns, it is recommended that measles immunization begin between twelve and fifteen months of age. Often, this program is part of a combination MMR vaccine, for measles, mumps, and rubella (German measles). A second booster is given following elementary school. The American Academy of Pediatrics does not consider a third vaccination to be necessary if the approved routine has been followed. It is recommended that children who were first immunized prior to their first birthday should receive boosters at fifteen months of age and again at age twelve. Indications are that immunity from vaccination is long term, if not lifelong. Recovery from natural infection results in a lifelong immunity to measles.

Inconsistency of the first generation of vaccine resulted in ineffective immunity among some individuals vaccinated during the 1960s. A number of small outbreaks during the 1980s were the result. Most cases of measles, however, have occurred in individuals who failed to be immunized.

Perspective and Prospects

The origin and early history of measles is uncertain, as the first authentic description of measles as a specific entity was that by the Arab physician al-Razi (Rhazes) in a 910 CE treatise on smallpox and measles. Rhazes quoted earlier work by the Hebrew physician El Yehudi, so it is likely that familiarity with these respective illnesses had existed for some time.

Measles is entirely a human disease, with no known animal reservoir. Consequently, the paucity of human populations of sufficient size to maintain transmission means that the spread of such an epidemic disease would have been unlikely before 2500 BCE. It is probable that the disease entered the human species through adaptation of the similar animal viruses of rinderpest or distemper. The absence of any description of a disease like measles in the writings of Hippocrates (c. fourth century BCE) likewise renders it unlikely that the disease was widespread before that date.

Epidemic disease with a rash characteristic of measles is known to have spread through the Roman Empire during the early centuries of the common era. The difficulty in differentiating measles from smallpox by the physicians of the time contributes to the difficulty in understanding the history of the illness. It is certain that by the time of Rhazes, measles had become common in the population.

The terminology of measles lent further confusion during the Middle Ages. Measles was often referred to as morbilli, a Latin term meaning “little disease,” to distinguish it from il morbo, or plague. The word measles first appeared in the fourteenth century treatise Rosa Anglica, by John of Gaddesden. The term may have been applied initially to the sores on the legs of lepers (mesles), and it was only later that illnesses characterized by similar rashes (measles, smallpox, and rubella) were clearly differentiated by European physicians. The significance of a rash with a white center in the mouth was probably recognized by John Quier in Jamaica and Richard Hazeltine in New England during the latter portion of the eighteenth century, but it was in 1896 that the American pediatrician Henry Koplik firmly reported its role in early stages of the disease.

Measles followed the path of European explorers to the Americas during the sixteenth century. Repeated outbreaks of measles devastated American Indian populations, which had minimal immunity to the newly introduced disease. The most thorough epidemiological investigation of measles newly introduced into a population was that by Peter Panum in his study Observations Made During the Epidemic of Measles on the Faroe Islands in the Year 1846 (1940). In the population of 7,864 persons, 6,100 became ill, with 102 deaths. Mortality rates as high as 25 percent were not unusual in previously unexposed populations. In Hawaii in 1848, about 40,000 deaths occurred among the population of 150,000 persons following the introduction of measles. Even higher mortality rates probably occurred among the populations of Peru and Mexico in 1530–31, following their exposure to infected Spanish explorers.

The earliest attempt at immunization was probably that of Francis Home of Edinburgh in 1758. Home soaked cotton in the blood of measles patients and placed it on the small cuts on the skin of children. The viral nature of measles was first demonstrated by John Anderson and Joseph Goldberger of the United States Public Health Service, who in 1911 induced the disease in monkeys using filtered extracts from human tissue. In 1954, the virus itself was isolated by John Enders, who grew the agent in human and monkey tissue in a laboratory.

The first effective vaccine was developed by Enders in 1958 using an attenuated (live) form of the virus. The vaccine was tested and then licensed in 1963. Several variations of the vaccine that proved superior in producing long-term immunity were developed in the decades that followed. In 1974, the World Health Organization (WHO) introduced a widespread vaccination program within developing countries.

The absence of any natural reservoir for measles other than humans has made the eradication of the disease possible. Active immunization of children in the United States reduced the annual incidence of the disease from 482,000 reported cases in 1962 to fewer than 1,000 in the late 1990s. The Measles and Rubella Initiative, a collaboration between the WHO, UNICEF, American Red Cross, US Centers for Disease Control and Prevention (CDC), and UN Foundation, has vaccinated one billion children worldwide since 2000. While widespread vaccination and worldwide surveillance has made global eradication of the disease a realistic possibility, the WHO reports that more than twenty million people contract measles each year and that it remains one of the top killers of children around the world, causing 145,700 deaths in 2013. Most of these fatalities occurred in children younger than five.

Outbreaks in 2014 and 2015

Though the CDC reports that measles was declared eliminated (no longer endemic or constantly present) in the United States as of 2000 becuase of access to effective vaccination, a record number of cases were reported in 2014. Of the 644 cases that occurred throughout twenty-seven states that year, the CDC stated that the majority of people who suffered from the infection were unvaccinated; the incident was linked to travelers coming to the country from the Philippines, which had recently suffered an outbreak. At the beginning of the following year, yet more measles outbreaks were highly publicized. From January to the end of February, the CDC confirmed that 170 people from seventeen states had measles. Most of these cases were considered part of an ongoing outbreak that experts believed began when an infected traveler visited a California amusement park. Aside from this outbreak, three other unrelated outbreaks were reported in Illinois, Nevada, and Washington state. The CDC issued an official Health Advisory in January to inform health care providers about the incidents and the ongoing investigations. At the state level, by the beginning of March lawmakers in several states started pushing for stricter regulations regarding nonmedical exemptions for vaccination; the surgeon general stressed the importance of vaccinating children.

Bibliography

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Woolf, Alan D., et al., eds. The Children’s Hospital Guide to Your Child’s Health and Development. Cambridge: Perseus, 2002. Print.

What did Atticus think Mayella did wrong in chapter twenty of To Kill A Mockingbird?

Atticus, in his summing up, says that Mayella Ewell has "put a man's life at stake" (i.e., Tom Robinson's), "in an effort to get rid of her own guilt."

He then clarifies that Mayella was not guilty of a crime, but she was guilty of breaking a rigid social code:

"... a code so severe that whoever breaks it is hounded from our midst as unfit to live with. ... She was white, and she tempted a Negro.  She did something that in our society is unspeakable: she kissed a black man.  Not an old Uncle, but a strong young Negro man.  No code mattered to her before she broke it, but it came crashing down on her afterwards."

Notice that Atticus does not say this social code is right, merely that Mayella Ewell knew she was "guilty" of breaking it.  He goes on to say that, in order to escape the severe consequences that would come her way if she admitted what she'd done (social ostracism, and probably more savage beatings from her father), Mayella desperately tried to blame Tom Robinson by accusing him of rape.  

Atticus has great sympathy for Mayella.  He knows she leads a lonely life, and that Tom Robinson was the only person in her world who was kind to her.  He understands why she was tempted.  However, he cannot spare her feelings by keeping her secret.  He must bring her secret out in order to save Tom Robinson's life. 

What are the main themes in the play Loyalties by John Glasworthy?

It is an irony that one of the main themes of Loyalties is the concept of loyalty. Each character has a different person or concept to which he or she is loyal.  Captain Dancy misjudges the loyalty of his friends.  Mabel is fiercely loyal to her mate.  Winsor is loyal to tradition.  Canynge is loyal to his reputation in the Army.  Most importantly, De Levin and Jacob Twisden are the only people loyal to the truth.  Of course, De Levin is the victim.  Jacob Twisden is the lawyer.

COLFORD.  Guilty or not, you ought to have stuck to him—it's not playing the game, Mr Twisden.

TWISDEN. You must allow me to judge where my duty lay, in a very hard case.

Yet another theme is that of discrimination.  In fact, this is the most general of themes to notice about this play.  In short, it is Jewish people (and especially De Levin) who are discriminated against.  He is trying to gain membership to the Jockey Club.  The rich people do not want to allow him membership and, as a result, stage a robbery.  De Levin decides to find the real culprit behind this robbery and find the only person he can trust is Twisden.

When you first read the story "A Rose for Emily" by William Faulkner, when did you realize how it would end? What is your response to the end?

Obviously the answer to when an individual reader figures out that Emily has murdered Homer Barron years ago will vary greatly. Having taught this story for several years to high school students, I can attest to the fact that most students don't figure it out until the very end, and many students are still confused about what happened even when they have finished the story. The jumbled timeline is one way that Faulkner keeps his readers off balance, making it less likely that they will guess what Emily did in her thirties. Most people have a good idea that when Emily is buying rat poison, she wants to murder someone with it because she asks for the strongest poison the druggist has and refuses to say what she wants it for. But since the issue of the horrible smell around Emily's house is reported in section II of the story and Homer Barron's disappearance is described in section IV, many readers have a hard time reconstructing the timeline while they are reading the story to make the smell come shortly after Barron's disappearance. In addition, the fact that Emily ordered what seemed to be wedding gifts for Barron seems inconsistent with her wanting to poison him. Not only that, but Miss Emily's family servant who stays with her until her death seems a mute testimony that nothing too horrific can have gone on under her roof, to say nothing of her opening up her home for china-painting lessons. Therefore, most readers can be forgiven for being completely in the dark until the third paragraph from the end.

Regarding the ending, especially the suggestion of necrophilia, most people are, to put it in student language, "grossed out" by it. Readers tend to be first disgusted, then surprised, and then confused. Only when they take time to look back over the story do they come to appreciate Faulkner's skill in weaving this unusual and creepy story. 

What are some examples of selflessness in the novel To Kill a Mockingbird?

There are several examples of selfless behavior throughout the novel To Kill a Mockingbird. The most notable example being Atticus' decision to selflessly defend Tom Robinson in front of a prejudiced community. Despite the impossible odds, Atticus takes the challenge head on and risks his reputation, and also puts his family in harms way, by choosing to defend an innocent black man. Another example takes place in Chapter 3, when Little Chuck Little stands up to Burris Ewell and selflessly defends Miss Caroline's character in front of the class. Despite his small stature, Chuck Little does not waver when Burris Ewell looks towards him and even threatens Burris by putting his hand into his pocket, indicating that he is carrying a blade. At the end of the novel, Boo Radley risks his life by defending Jem and Scout while Bob Ewell is attacking them. Bob Ewell was armed, and Boo Radley left the safety of his home to wrestle Bob away from the children to save their lives. His selfless act prevented Bob Ewell from possibly murdering Jem and Scout, and Atticus is eternally grateful.

What are brain tumors?

Causes and Symptoms

The earliest symptom of a brain tumor may be a persistent headache, although this symptom does not necessarily stem from a brain tumor. Nevertheless, when headaches occur regularly, it is essential that the cause be investigated as early as possible and a diagnosis made.

As brain tumors continue to grow and crowd the brain, other symptoms become evident. Even though such tumors are frequently benign, they can become disabling. As brain tissue and the nerve tracks inside the skull are compressed by the incursion that such tumors make on them, patients may suffer muscle weakness, dizziness, loss of vision, reduction of hearing, nausea, speech problems, emotional problems, disorientation, and sometimes seizures.

Brain tumors can, but rarely, enhance mental functioning. Nearly always, they cause impairment across a range of mental aptitudes. Memory loss is common, as are unexplained mood swings. A tumor that grows so that it restricts the flow of cerebrospinal fluid will cause an additional condition, hydrocephalus. Hydrocephalus, also known as “water on the brain,” is when the cerebrospinal fluid flows into brain tissue itself. This swelling quickly becomes painful and is lethal if not reduced.

The incidence of brain tumors is small, representing about 1.3 percent of cancers diagnosed in the United States in a given year. Two age groups are at greater risk than the general population. Adult males between fifty-five and sixty-five years of age seem to be vulnerable to primary brain tumors, and children between three and twelve years of age also have a higher incidence of this condition.

The causes of brain tumors have not been fully determined. It has been noted that genetic factors may play a role in the development of such tumors in young people, particularly those with a parent who has had colon
cancer or cancer of the salivary glands or nervous system. Children exposed to high energy radiation applied to the head in the treatment of leukemia
or who develop neck or facial cancers suffer an increased risk of developing brain tumors.

Among adults, those whose work exposes them to vinyl chloride have a high incidence of brain tumors, as do those whose work involves exposure to lead in such industries as mining, printing, and chemical industries. Those who suffer from epilepsy are at higher risk of developing gliomas, tumors arising from brain substance, some 60 percent of which are malignant. The risk seems less in people whose diets include little fat and refined sugar and plentiful fresh fruits and vegetables.

Many brain tumors develop from tissues within the skull, but others result from the metastasis, or spread of cancer cells from malignancies elsewhere in the body, often the lungs or breasts. Of the 170,000 Americans who develop lung cancer annually, about 55,000 will also develop brain tumors. Adults who have had organ transplants are also at increased risk.

Treatment and Therapy

Where a brain tumor—malignant or benign—exists, the preferred treatment is surgical removal by opening the skull. Such delicate surgery is performed by a neuro-oncological surgeon who understands the brain’s contours and their relationship to the nervous system and spinal cord.

Such diagnostic tools as computed tomography (CT) scanning and magnetic resonance imaging (MRI) can determine the extent of a brain tumor before a decision is made about how to treat the condition. Sometimes surgery is not indicated because the tumor is embedded in vital areas of the brain that would be irreparably damaged by removal.

In such cases, radiation may be used initially to shrink the tumor, sometimes to the point that eventually it can be removed surgically. In other cases, it may be possible to remove part of the tumor, thereby releasing the pressure that it exerts on the brain. Partial removal is usually followed by a course of radiation and/or chemotherapy, generally with the expectation that additional surgical removal will occur if the tumor decreases in size.

Corticosteroids have in some cases succeeded in controlling the swelling of tumors so that pressure on the brain is reduced and symptoms are mitigated.

Perspective and Prospects

In the United States, brain tumors do not occur frequently. The American Cancer Society estimates that in 2013 there will be about twenty-three thousand new cases of primary brain and other nervous system cancers, and about fourteen thousand deaths related to such cancers. The life of one child in every three thousand in the population ends before age ten because of a primary brain tumor. Some fifteen hundred children are diagnosed every year with brain tumors, most located in the cerebellum, the midbrain, or the optic nerve.

There has been an increase in primary brain tumors among the elderly since 1980, while the percentage of resulting deaths has decreased. In viewing such statistics, one must remember that with advances in medical technology, more people are achieving old age and are developing diseases when, fifty years ago, they would not have still been living.

Advances in cell research and in the development of drugs that control and, in some cases, eliminate specific cancer cells provide encouragement that medical progress is being made consistently. Neuro-oncological surgery has undergone great advances and will likely substantially reduce the threat of human error as sophisticated robotic surgical procedures are developed. Although cancer is still a scourge, recent medical research offers realistic hope of controlling it.

Bibliography:

American Cancer Society. Cancer Facts & Figures 2013. Atlanta, Ga.: American Cancer Society, 2013.

Jasmin, Luc. "Brain tumor—Primary—Adults." MedlinePlus, Nov. 2, 2012.

Register, Cheri. The Chronic Illness Experience: Embracing the Imperfect Life. City Center, Minn.: Hazelden, 1999.

Roloff, Tricia Ann. Navigating Through a Strange Land: A Book for Brain Tumor Patients and Their Families. 2d ed. Minneapolis, Minn.: Fairview, 2001.

Shiminski-Maher, Tania, Patsy Cullen, and Maria Sansalone. Childhood Brain and Spinal Cord Tumors: A Guide for Families, Friends, and Caregivers. Sebastopol, Calif.: O’Reilly, 2002.

Stark-Vance, Virginia, and M. L. Dubay. One Hundred Questions and Answers About Brain Tumors. 2d ed. Sudbury, Mass.: Jones, 2011.

Wood, Debra. "Brain Tumor and Brain Cancer—Adult." Health Library, Jan. 18, 2013.

Zeltzer, Paul M. Brain Tumors: Leaving the Garden of Eden. Encino, Calif.: Shilysca, 2004.