Zoonoses

Introduction

Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

BIBLIOGRAPHY

Introduction

A zoonosis (pronounced ZOO-oh-NO-sis) is a disease that can be transmitted from animals to humans under natural conditions. Some zoonoses, after being transmitted from animals to humans, can be transmitted from human to human. There are hundreds of zoonoses, including some of the most deadly diseases known. For example, avian influenza (flu) pandemics begin as zooneses transmitted from birds, and malaria is transmitted by mosquitoes and kills about a million people annually. New zoonoses have been emerging in recent years with increased frequency due partly to the incursion of increasing human populations into animal habitats. The World Health Organization (WHO) said in 2007 that 75% of new communicable human diseases that have emerged over the last 10 years are zoonoses caused by pathogens found in animals or animal products. Zoonoses are found in all societies, but are most common and most deadly in poorer countries.

Disease History, Characteristics, and Transmission

Many zoonoses have afflicted human beings throughout their history. Before the development of agriculture in approximately 8,000 BC, people lived in small nomadic groups. Because their diet included wild game, they were prone to parasitic zoonotic diseases, such as hookworm. However, members of such groups who survived to adulthood tended to be healthy. Because of the relative mutual isolation of these groups, epidemic disease was rare.

After the domestication of plants and food animals, people began to live in larger groups and in closer contact with a variety of animals, including sheep, pigs, cattle, goats, and chickens. This made the transmission of diseases from animals to humans more likely, as well as the transmission of diseases from person to person. Tuberculosis, measles, smallpox, and influenza first entered human populations through agricultural contact with animals and animal products, and new influenza strains still are transmitted to human populations from domesticated pig and bird populations in Asia.

The development of global trade routes allowed the spread of epidemic diseases that had lost all connection with their original animal hosts, as well as of diseases that remained zoonotic, such as bubonic plague. Bubonic plague, which is caused by the bacterium Yersinia pestis, first appeared in Europe in 542 AD, but it only devastated the European population after 1346, when fleainfested furs were brought from China over recently opened trade routes. In a few years this zoonosis killed approximately one-third of the population of Europe and about 75 million people worldwide. Bubonic plague is maintained in rodent populations and transmitted to humans by flea and rodent bites.

Since the development of powered transportation in the nineteenth century, a whole new set of opportunities has arisen for zoonoses to travel the world. Migrant workers, political and economic refugees, tourists, and military personnel move quickly and in large numbers from one part of the world to another. Animals and animal products are moved globally by airplane and ship, sometimes inadvertently, as when rats and insect eggs are transported along with cargo. The tiger mosquito may have hitchhiked from Asia to the United States in worn tires shipped from the United States to Japan for retreading and then returned to the United States. Some experts warn that these mosquitoes may contribute to increased zoonotic transmission of North American viruses, including the LaCrosse virus, as they spread. The West Nile virus, which produced a notorious outbreak in 1999 and is transmitted to humans through mosquito bites, was apparently brought to the United States from Israel on an airplane, either by a stowaway mosquito or an infected human traveler.

Zoonoses can be transmitted to humans by bites, scratches, saliva, dander (skin flakes, similar to dandruff), droppings, and blood. Certain zoonoses, such as trichinellosis, are transmitted when humans eat the flesh of certain animals. Dog and bat bites can transmit rabies, cat bites can transmit cat-scratch fever, monkey bites can transmit hepatitis B, and rat bites can transmit leptospirosis, bubonic plague, salmonellosis, and rat-bite fever.

WORDS TO KNOW

EMERGING INFECTIOUS DISEASE: New infectious diseases such as SARS and West Nile virus, as well as previously known diseases such as malaria, tuberculosis, and bacterial pneumonias that are appearing in forms that are resistant to drug treatments, are termed emerging infectious diseases.

HOST: Organism that serves as the habitat for a parasite, or possibly for a symbiont. A host may provide nutrition to the parasite or symbiont, or simply a place in which to live.

RE-EMERGING INFECTIOUS DISEASE: Re-emerging infectious diseases are illnesses such as malaria, diphtheria, tuberculosis, and polio that were once nearly absent from the world but are starting to cause greater numbers of infections once again. These illnesses are reappearing for many reasons. Malaria and other mosquito-borne illnesses increase when mosquito-control measures decrease. Other diseases are spreading because people have stopped being vaccinated, as happened with diphtheria after the collapse of the Soviet Union. A few diseases are reemerging because drugs to treat them have become less available or drug-resistant strains have developed.

RESERVOIR: The animal or organism in which the virus or parasite normally resides.

VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.

Animals serve as the natural reservoir of some zoonotic diseases, and the vector of others. A reservoir is a long-term host organism that maintains an infective agent, usually a virus, bacteria, or parasite. The reservoir is usually not affected by the agent or is without symptoms, and can then pass on the infectious agent either by direct contact, or through a vector. A vector transfers an infectious agent from an infected host to an uninfected animal or human. Vectors are often arthropods, a group of invertebrate animals including insects. For example, birds are a natural reservoir of West Nile virus, and the disease is transmitted to humans by a mosquito vector.

Some experts reserve the term “zoonosis” for a disease that is transmitted to humans from vertebrate animals, that is, animals with spinal columns, such as cattle, dogs, cats, and rats. By this definition, diseases spread to humans by insect bites are not zoonoses, but disease or death cause by the bites of venomous snakes and fishes are. Snake bites kill over 30,000 people per year worldwide, mostly in Asia.

Scope and Distribution

The geographical distribution of any given zoonosis depends on the geographical distribution of its host animal or animals. All parts of the world are affected by zoonotic diseases. While most zoonoses are most common in less developed countries in Asia, Africa, and South America, a few, such as Lyme disease and trichinellosis, are more common in North American and Europe. Millions of people get sick each year from food-borne bacterial zoonoses, such as E. coli, salmonellosis, campylobacteriosis, anthrax, and brucellosis. Cystericercosis, a zoonosis caused by a parasite that lives in pigs, can cause headache and epilepsy and infects approximately one out of every 1,000 inhabitants of Latin America. Viral zoonoses include rabies, which kills about 55,000 people every year worldwide (mostly from dog bites). Avian influenza, a viral zoonosis that derives its name from the fact that the animal reservoir for the virus is birds, could infect a large part of the human population if it combined with other viruses or mutated in such a way as to become transmissible directly between humans. Experts fear that tens or hundreds of millions of people could die in an pandemic outbreak of such a virus, as occurred in 1918, when between 50 and 100 million people died during the Spanish influenza pandemic.

Treatment and Prevention

Treatment of zoonoses varies by infection type. Zoonoses can be caused by viruses, bacteria, parasites, and fungi. Bacterial infections can usually be combated with antibiotics; antifungals, antiparasitics, and antivirals may be used against other infections, but options are generally more limited for fighting non-bacterial infections. For example, there is no available treatment for West Nile virus, which can cause fatal encephalitis in some victims. Treatment of West Nile is supportive, that is, directed at relieving symptoms and helping the patient's own immune system fight off the infection, if it can.

Prevention of zoonoses is primarily aimed at reducing the incidence of the zoonosis in the animal population from which it is transmitted to humans. For example, destroying rabid dogs decreases the incidence of rabies in humans. Spraying DDT to keep down mosquito populations that can transmit malaria and other diseases has a similar effect. Veterinary medicine and human medicine must cooperate in many of these measures designed to reduce zoonotic disease.

Humans can also decrease the likelihood of contracting a zoonotic disease by avoiding contact with infected animals and their feces and infected food products. Food products may be rendered safe by excluding infected animals from the food supply, as in the case of anthrax or trichinellosis, or by improved food preparation (e.g., pasteurizing, thorough cooking, slaughter-house sanitation).

Impacts and Issues

Over 200 zoonoses are known, and more are emerging all the time. As long as an expanding human population continues to encroach on animal habitats, the likelihood that more zoonotic diseases will appear remains high. As noted earlier, 75% of recently emerging or re-emerging diseases are zoonoses. These include unconventional diseases such as prion diseases (transmissible spongiform encephalopathies), which are caused not by viruses or living organisms but by deformed proteins that, when ingested, cause similar protein deformation in the animal or human that has eaten the meat. These deformed proteins can accumulate in the central nervous system and cause mental degeneration and death. However, an emergent pathogen need not be unknown or unusual. A disease is considered emerging if it appears in an area where it has not previously been reported, as, for example, West Nile virus appearing in the United States.

See AlsoAnimal Importation; Arthropod-borne Disease; Bovine Spongiform Encephalopathy (“Mad Cow” Disease); Brucellosis; Cat Scratch Disease; Dengue and Dengue Hemorrhagic Fever; Ebola; Emerging Infectious Diseases; Giardiasis; Hantavirus; Lyme Disease; Malaria; Prion Disease; Rat-Bite Fever; Ringworm; Trichinellosis.

BIBLIOGRAPHY

Books

Krauss, Hartmut. Zoonoses: Infectious Diseases Transmissible from Animals to Humans. Washington, DC: ASM Press, 2003.

Torrey, E. Fuller, and Robert H. Yolken. The Beasts of the Earth: Animals, Humans, and Disease. Piscataway, NJ: Rutgers University Press, 2005.

Periodicals

Chomel, Bruno B., et al. “Wildlife, Exotic Pets, and Emerging Zoonoses.” Emerging Infectious Diseases 13 (January 2007): 6–11. Also available online at: <http://www.cdc.gov/ncidod/eid/13/1/6.htm> (accessed May 11, 2007).

Meslin, F.-X. “Global Aspects of Emerging and Potential Zoonoses: a WHO Perspective.” Emerging Infectious Diseases 3 (April-June 1997): 223–228. Also available online at: <http://www.cdc.gov/ncidod/eid/vol3no2/meslin.htm> (accessed May 11, 2007).

O'Brien, Sarah J. “Foodborne Zoonoses.” British Medical Journal 331 (November 26, 2005): 1217–1218. Also available online at: <http://www.bmj.com/cgi/content/full/331/7527/1217> (accessed May 11, 2007).

Web Sites

San Diego Natural History Museum. “Zoonoses: Animal-borne Diseases.” <http://www.sdnhm.org/fieldguide/zoonoses/index.html> (accessed February 27, 2007).

World Health Organization. “Report of the WHO/FAO/OIE Joint Consultation on Emerging Zoonotic Diseases.” 2004. <http://whqlibdoc.who.int/hq/2004/WHO_CDS_CPE_ZFK_2004.9.pdf> (accessed February 28, 2007).

Zoonoses

What Are Zoonoses?

Are They Contagious?

Some Examples of Zoonoses

How Are Zoonoses Treated?

How Are Zoonoses Prevented?

Resources

Zoonoses (zoh-ah-NO-seez) are infections that humans contract from animals.

KEYWORDS

for searching the Internet and other reference sources

Cat scratch disease

Hantavirus

Lyme disease

Plague

Psittacosis

Rabies

Toxoplasmosis

Trichinosis

What Are Zoonoses?

Zoonoses are infections caused by parasites, bacteria, or viruses that are passed from animals to humans. Most people contract zoonotic (zoh-uh-NAH-tik) infections from animals with which they have a lot of contact, such as pets or farm animals. Wild animals and insects can be the source of disease, too, particularly for diseases spread by the bite of a tick, mosquito, or fly. Animals such as wild rodents and bats also can carry diseases that may be harmful to humans.

Zoonoses can cause minor or serious illness. In some cases, the organisms involved infect people, but they do not become ill. Other zoonoses can be very dangerous to people, especially anyone with an immune system weakened by age or illness.

Are They Contagious?

Most of these infections do not spread from person to person or do so only in rare instances. Usually they are spread from animals to humans in the following ways:

• from the bite of an infected insect
• through contact with an animal’s feces* or urine, either through the mouth or by breathing in dust from dried feces

*feces

(FEE-seez) is the excreted waste from the gastrointestinal tract.

• from the bite or scratch of an infected animal
• from eating the meat of an infected animal

Some Examples of Zoonoses

Cat scratch disease

A cat carrying Bartonella henselae (bar-tuh-NEH-luh HEN-suh-lay), the bacterium responsible for cat scratch disease, usually does not have symptoms, but if the bacteria are passed to a human through a scratch or bite, a person may experience skin sores, swollen and sore lymph nodes*, extreme tiredness, headaches, and fever. Antibiotics may be prescribed to treat the infection.

*lymph

(LIMF) nodes are small, bean-shaped masses of tissue that contain immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

Psittacosis

People who have contact with birds may be at risk for psittacosis (sih-tuh-KO-sis), also known as parrot fever. If a person inhales bird feces or urine particles while cleaning a bird’s cage, he or she may develop symptoms of pneumonia (nu-MO-nyah, inflammation of the lung), such as fever, coughing, or chest pain. Antibiotics are used to treat psittacosis.

Rabies

A virus that is carried in the saliva of infected animals can cause rabies when transmitted through a bite or, less commonly, through contact with saliva. Symptoms include fever, difficulty swallowing, delirium*, seizures*, and coma*. Death can result if the infection is not treated. Treatment includes intensive care in a hospital. A series of vaccinations* started at the time of a bite from a possibly infected animal can prevent the person from developing the disease. Many mammals, especially raccoons, bats, and dogs, may be infected with rabies, but human rabies is rare in the United States. According to the U.S. Centers for Disease Control and Prevention, there were no cases of rabies in humans in the United States in 2000. In many other countries, especially those in the developing world, rabies is much more common.

*delirium

(dih-LEER-e-um) is a condition in which a person is confused, is unable to think clearly, and has a reduced level of consciousness.

*seizures

(SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.

*coma

(KO-ma) is an unconscious state in which a person cannot be awakened and cannot move, see, speak, or hear.

*vaccinations

(vak-sih-NAY-shunz), also called immunizations, are the giving of doses of vaccines, which are preparations of killed or weakened germs, or a part of a germ or product it produces, to prevent or lessen the severity of a disease.

Plague

Plague (PLAYG) is a bacterial infection caused by Yersinia pestis (yer-SIN-e-uh PES-tis). Plague can be transmitted to humans through the bite of a flea that has become infected through contact with an infected rodent, such as a rat. The disease causes such symptoms as fever and swollen lymph nodes. In some cases the infection spreads through the blood and can infect the lungs. If this happens, plague can spread from person to person through coughing or sneezing. Plague was the cause of huge epidemics* in Europe and Asia during the Middle Ages, and it is still seen in many developing countries. It is seen in many developed countries too, including the United States, although not as many cases occur. The disease can be fatal if it is not treated with antibiotics.

*epidemics

(eh-pih-DEH-miks) are outbreaks of diseases, especially infectious diseases, in which the number of cases suddenly becomes far greater than usual. Usually epidemics are outbreaks of diseases in specific regions, whereas worldwide epidemics are called pandemics.

Hantavirus

Rodents, such as mice and rats, may carry hantavirus (HAN-tuh-vy-rus). This virus can spread to humans when they inhale particles from rodent feces, saliva, or urine. People infected with hantavirus can develop hantavirus pulmonary (PUL-mo-nar-ee) syndrome (HPS), which causes such symptoms as fever, headaches, muscle aches, nausea (NAW-zee-uh), vomiting, diarrhea (dye-uh-REE-uh), abdominal* pain, and chills. In severe cases a person may experience shortness of breath and the lungs may fill with fluid. There is no cure for hantavirus infection, but people who have HPS typically are hospitalized in an intensive care unit, where they receive oxygen and other types of supportive care.

*abdominal

(ab-DAH-mih-nul) refers to the area of the body below the ribs and above the hips that contains the stomach, intestines, and other organs.

Lyme disease Borrelia burgdorferi (buh-REEL-e-uh burg-DOR-fe-ree) bacteria inside an infected tick can cause Lyme (LIME) disease in humans after a tick attaches to the skin and feeds on a person’s blood. Ticks pick up the bacterium by feeding on the blood of infected deer and mice, which serve as reservoirs for the organism. Lyme disease can produce a number of symptoms, such as extreme tiredness, muscle aches, and swollen, painful joints. At the site of the tick bite, some people develop a bull’s-eye rash, a red rash surrounded by rings that resembles a bull’s-eye target. A person with Lyme disease usually is treated with antibiotics.

Toxoplasmosis

Eating contaminated meat or having contact with the feces of an infected cat can put a person at risk for toxoplasmosis (tox-o-plaz-MO-sis). This zoonosis is caused by a parasite and can produce such symptoms as swollen lymph nodes, muscle aches, headaches, and sore throat in a healthy person and life-threatening brain infections in people with weakened immune systems, especially those who have HIV/AIDS*. If a pregnant woman becomes infected with the parasite, she can transmit the infection to her unborn baby, which can lead to a number of health problems in the child.

*AIDS ,

or acquired immunodeficiency (ih-myoo-no-dih-FIH-shen-see) syndrome, is an infection that severely weakens the immune system; it is caused by the human immunodeficiency virus (HIV).

Trichinosis

If people eat meat (especially pork products, such as sausage or ham) infected with the eggs of Trichinella (trih-kih-NEH-luh) worms, they can contract trichinosis (trih-kih-NO-sis), a disease that produces such symptoms as diarrhea, vomiting, and abdominal pain. Trichinosis can cause nerve and muscle damage as well as heart and lung problems. It can be treated with medication.

How Are Zoonoses Treated?

The treatment of a zoonotic infection depends on the specific disease, but many are treatable with prescription medications, such as antibiotics.

How Are Zoonoses Prevented?

Because household pets may carry zoonotic organisms, it is important to keep pets healthy and vaccinated to avoid infection. Some other ways people can protect against zoonoses include:

• having pets regularly examined by a veterinarian
• avoiding contact with stray, unfamiliar, or wild animals
• cleaning litter boxes daily and animal cages frequently to prevent the growth of bacteria and parasites
• having someone who does not have a weakened immune system and is not pregnant empty pet litter boxes, bathe pets, clean pet cages, and pick up pet feces
• cooking meat until it is no longer pink inside and the juices run clear
• washing hands with soap and warm water after handling animals and before eating
• clearing brush and other areas around the house where rodents might live
• not storing food or trash in an area where it could attract animals
• wearing long sleeves and long pants when outdoors, especially in wooded areas, to discourage tick and mosquito bites
• using insect and mosquito repellent
• examining the body and pets for ticks after spending time outside in areas where ticks are found

See also

Cat Scratch Disease

Chlamydial Infections

Lyme Disease

Plague

Rabies

Toxoplasmosis

Trichinosis

Resources

Organization

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC tracks various zoonoses, the areas where they occur, and how many people are infected at any given time. It offers information on specific zoonoses at its website.

Telephone 800-311-3435 http://www.cdc.gov

Website

KidsHealth.org. KidsHealth is a website created by the medical experts of the Nemours Foundation and is devoted to issues of children’s health. It contains articles on a variety of health topics, including cat scratch disease, Lyme disease, psittacosis, rabies, and other zoonoses.

http://www.KidsHealth.org

ZOONOSES

Zoonoses, or zoonotic diseases, are caused by infectious agents that are transmissible under natural circumstances from vertebrate animals to humans. Zoonoses may arise from wild or domestic animals or from products of animal origin. Zoonoses have been known since early hystorical times. There are biblical references to plague, a bacterial zoonosis mainly transmitted to humans by fleas; and some historians contend that a disease first described by Thucydides during the Plague of Athens (430–425 b.c.e.) was typhus, a louse-borne zoonosis (Zinsser). Certain zoonoses, such as yellow fever, malaria, and rabies, are well known to the general public, but a vast number of lesser-known zoonoses exist in limited cycles in different parts of the world. There are undoubtedly many zoonoses lurking in nature that have the potential to cause serious public health consequences if introduced into humans. This is, in fact, what may be our greatest concern about zoonoses—not the diseases that we know they are capable of causing, but the hidden potential of what diseases might arise in the future. Examples that foster our concern include the emergence of AIDS (acquired immunodeficiency syndrome) from nonhuman primates, which has developed into one of the most significant infectious disease threats in the world today, and the crossing of the species barrier of certain influenza virus strains that have led to large human pandemics. Diseases such as AIDS and influenza have their origins as zoonoses, but they subsequently adapted to human-to-human transmission.

There are a number of different types of microbial agents that cause zoonotic diseases, and various ways humans can become infected with these agents. This may best be explained by a few examples: (1) Lyme disease, a bacterial disease transmitted via the bite of an infected tick;(2) rabies, a viral disease acquired by the bite of an infected animal; (3) Ebola hemorrhagic fever, a viral disease spread by infected blood, tissues, secretions, or excretions; (4) hantaviral disease, a disease contracted by inhaling air contaminated with virus-infected excreta from rodents; (5) leptospirosis, a bacterial disease usually transmitted to humans through contact with urine from infected animals; (6) brucellosis, a bacterial disease contracted by ingestion of unpasteurized milk; and (7) cat-scratch disease, a disease contracted through bites or licks of infected cats.

Enteric bacteria such as Salmonella and Escherichia coli and parasites such as Cryptosporidium and Giardia are responsible for major food-borne and waterborne disease outbreaks around the world, and recently the nonmicrobial, transmissible agent of bovine spongiform encephalopathy (mad cow disease) appears to have crossed over to humans to produce a degenerative neurological disease known as variant Creutzfeldt-Jakob disease.

There has been a disturbing trend of reemergence of previously recognized zoonoses that were believed to be under control. This has been coupled with the emergence of new zoonotic diseases. Numerous factors may account for this, including: (1) alteration of the environment, affecting the size and distribution of certain animal species, vectors, and transmitters of infectious agents to humans; (2) increasing human populations causing an increased level of contact between humans and infected animals; (3) industrialization of foods of animal origin—that is, changes in food processing and consumer nutritional habits; (4) increasing movements of people, as well as an increased trade in animals and animal products; and (5) decreasing surveillance and control of some of the major zoonoses. Some supposedly "new zoonoses" have been around for a long time but have simply not been recognized. For example, several types of hantaviruses are transmitted by rodents such as deer mice and can cause the disease known as hantavirus pulmonary syndrome. This disease has likely been around for decades, if not centuries, but human cases were first documented only in 1993. In addition, global warming has the potential to broaden the geographic distribution and abundance of arthropods as well as the vertebrate hosts in which some zoonoses persist.

There is no single clinical picture that can be drawn of zoonoses, given the diverse group of microorganisms that are capable of causing zoonotic diseases. A partial list of symptoms may include some, but not all, of the following: fever (sometimes hemorrhagic), headache, rash, muscle aches, arthritis, respiratory distress (sometimes pneumonia), abdominal pain, vomiting, diarrhea, jaundice, cardiac abnormalities, and neurological involvement ranging from stiff neck to meningitis or encephalitis. The course of disease varies between different zoonotic pathogens but can be more severe in the very young or very old, or in individuals who are immunocompromised. Many zoonoses can be treated with antimicrobial drugs, but there are few drugs that can be used to successfully treat viral zoonoses. Treatment for a known or suspected exposure to a viral zoonosis such as rabies involves administration of immune globulin, whereas only supportive treatment can be offered for many other viral zoonoses.

Vaccines are available for the general public for a small number of zoonoses, such as Japanese encephalitis and yellow fever, and on a limited basis for individuals perceived to be at occupational or recreational risk. In addition, chemoprophylactic regimens such as antimalarial drugs are recommended for travellers to high disease-risk areas. The risk of contracting vector-borne diseases can be reduced by avoidance of areas infested by arthropods, use of insect repellents, and appropriate clothing (the less skin exposed the better). Occasionally it is possible to reduce zoonotic disease risks by decreasing the abundance of certain reservoir hosts such as rodents. Individuals should also not drink untreated water or unpasteurized milk. Areas containing potentially contaminated animal material such as rodent excreta should be cleaned using appropriate disinfectants. Patients with diseases such as Ebola virus should be kept in strict isolation. Diseases such as tularemia and leptospirosis may be contracted by handling infected animal tissue, so trappers should use gloves when handling dead animals.

The disease incidence and pattern of occurrence of zoonoses varies greatly between different regions within a country and between countries. In general, zoonoses do not occur in large numbers in the industrialized world. Because of this relative infrequency of occurrence, some zoonotic infections may be overlooked and underdiagnosed.

Certain individuals may be at greater risk for contracting zoonoses. These include people with occupational exposure, such as veterinarians, farmers, and slaughterhouse workers, or individuals who participate in outdoor recreational activities, such as hunters. The best defense against contracting zoonoses is education. Individuals should be aware of the respective zoonoses that may be circulating in their environment and the times of year of greatest risk for contracting these zoonoses. This type of information is generally available from public health departments and veterinarians, and can also be found on the Internet.

Harvey Artsob

(see also: Communicable Disease Control; Ecosystems; Epidemics; Epidemiology; Vector-Borne Diseases; Veterinary Public Health; and articles on diseases mentioned herein )

Bibliography

Lederberg, J.; Shope, R. E.; and Oaks, S. C. (1992). Emerging Infections. Microbial Threats to Health in the United States. Washington, DC: National Academy Press.

Meslin, F. X. (1997). "Global Aspects of Emerging and Potential Zoonoses: A WHO Perspective." Emerging Infectious Diseases, Vol. 3. Geneva: World Health Organization.

Zinsser, H. (1934). Rats, Lice, and History. Boston: Little, Brown.

Zoonoses

Zoonoses are diseases caused in humans by bacteria , viruses, parasites , and fungi that have been transmitted from animals, reptiles , or birds to people.

Because many of the microorganisms that cause zoonotic disease are normal inhabitants of domestic animals and birds, people who are involved in agriculture and those who work in food processing plants can be at risk for infection . Prevention of such infections is actively studied. Understanding the host factors that contribute to immunity from disease and which factors promote the establishment of disease is essential if zoonotic infections are to be successfully prevented.

Humans can develop zoonotic diseases by different routes, depending on the microorganism. For example, some bacteria can cause infection following entry through a cut in the skin. Another common method of disease transmission is by the inhalation of bacteria, viruses, or fungi. A third route is via the ingestion of improperly cooked food or water contaminated with the fecal material.

A classic example of a zoonotic disease is yellow fever . The discovery of the disease and of its origin came during the construction of the Panama Canal during the first decade of the twentieth century. The construction of the canal took humans into previously unexplored regions of the Central American jungle. This brought the workers into contact with animals and microorganisms that they had not been in contact with before. One of the microbes produced the serious illness that came to be called yellow fever.

Another example occurred beginning in the 1970s. Then, the clearing of the Amazonian rain forest to provide agricultural land accelerated. Woodcutters became ill with infections caused by the Mayaro and Oropouche viruses. Another final example dates back only a decade ago. In the mid 1990s, a rapidly developing and often-fatal lung infection in the Southwestern United States was found to be caused by the Hanta virus that can be transmitted from rodents to humans. A final example is the viral zoonoses called West Nile virus . This virus, which can infect birds such as crows and blue jays, can be transmitted to humans by a mosquito that feeds on the bird and then subsequently feeds on a human.

There are a variety of zoonotic diseases that are caused by the movement of bacteria from an animal , bird, or insect host to humans. Examples include Tularemia, which is caused by Francisella tulerensis, Leptospirosis (Leptospiras spp.), Lyme disease (Borrelia burgdorferi), Chlaydiosis (Chlamydia psittaci), Salmonellosis (Salmonella spp.), Brucellosis (Brucella melitensis, suis, and abortus), Q-fever (Coxiella burnetti), and Campylobacteriosis (Campylobacter jejuni).

Fungi also produce zoonoses. An example is Aspergillosis, which is caused by Aspergillus fumigatus.

Two protozoan zoonoses have emerged in accelerating numbers in the past two decades. One protozoan is called Giardia. The debilitating diarrhea that is commonly dubbed "beaver fever" is caused by drinking water that is contaminated with Giardia lamblia. Cryptosporidium parvum causes an equally debilitating diarrheal malady called cryptosporidiosis.

Giardia and Cryptosporidium live naturally in many wild animals. The loss of natural habitat with increasing human development has brought the animals and their microbial cargo into more frequent contact with people, and human infections are the result.

Human encroachment is also fueling the emergence of fatal viral hemorrhagic fevers such as Ebola and Rift Valley fever. The zoonotic origin of these agents is not definitively known. However, the available evidence strongly supports the idea that primate populations harbor the viruses, and that periodically transmission of the viruses from primates to humans occurs.

Beginning in 1986, an outbreak of bovine spongiform encephalopathy (BSE) among cattle in the United Kingdom led to the eventual slaughter of over 150,000 domestic animals. Ominously, scientists have evidence that links the "mad cow" disease in the domestic animals with the brain degeneration in humans known as Creutzfeld-Jacob disease. Although not conclusively established, there is the possibility that the disease-causing agent of Creutzfeld-Jacob disease was passed to some of the people when they ate infected beef.

The increasing incidence of these and other zoonotic diseases may be in part due to the increased ease of global travel. Microorganisms are global residents, which can easily move along with people and cargo. New combinations of microorganisms and susceptible human populations have and continue to arise. As of July 2003, the virus responsible for severe acute respiratory syndrome (SARS) was thought to be zoonotic in origin, but further research is needed to clarify origin and transmission modes.

See also Chimpanzees; Prions.

Resources

books

Hugh-Jones, M.E., H.V. Hagstad, and W.T. Hubbert. Zoonoses: Recognition, Control and Prevention. Ames: Iowa State University press, 2000.

organizations

Centers for Disease Control and Prevention, National Center for Infectious Diseases, Rabies Section, MSG-33. 1600 Clifton Road, Atlanta, GA 30333. October 23, 2001 [cited November 11, 2002] <http://www.cdc.gov/ncidod/dvrd/rabies/bats_&_rabies/bats&.htm>.

Los Angeles County Department of Animal Services. 3834 S. Western Ave., Room 238, Los Angeles, CA 90062. (323) 730–3723. [cited November 11, 2002]. <http://www.la publichealth.org/vet/guides/vetzooman.htm>.

World Health Organization. Avenue Appia 20, 1211 Geneva 27, Switzerland. (+41 22) 791 21 11. January 2002 [cited November 11, 2002] <http://www.who.int/health-topics/zoonoses.htm>.

Brian Hoyle

Zoonoses

Resources

Zoonoses are diseases caused in humans by bacteria, viruses, parasites, and fungi that have been transmitted from animals, reptiles, or birds to people.

As of 2006, avian influenza is poised to become potnetially a major zoonotic disease. The disease, which endangers human survival, can be transmitted from various species of birds to humans. It appears that the occurrence of the disease has begun to increase, particuarly in the far east.

Because many of the microorganisms that cause zoonotic disease are normal inhabitants of domestic animals and birds, people who are involved in agriculture and those who work in food processing plants can be at risk for infection. Prevention of such infections is actively studied. Understanding the host factors that contribute to immunity from disease and which factors promote the establishment of disease is essential if zoonotic infections are to be successfully prevented.

Humans can develop zoonotic diseases by different routes, depending on the microorganism. For example, some bacteria can cause infection following entry through a cut in the skin. Another common method of disease transmission is by the inhalation of bacteria, viruses, or fungi. A third route is via the ingestion of improperly cooked food or water contaminated with the fecal material.

A classic example of a zoonotic disease is yellow fever. The discovery of the disease and of its origin came during the construction of the Panama Canal during the first decade of the twentieth century. The construction of the canal took humans into previously unexplored regions of the Central American jungle. This brought the workers into contact with animals and microorganisms that they had not been in contact with before. One of the microbes produced the serious illness that came to be called yellow fever.

Another example occurred beginning in the 1970s. Then, the clearing of the Amazonian rain forest to provide agricultural land accelerated. Woodcutters became ill with infections caused by the Mayaro and Oropouche viruses. Another example dates back only a decade ago. In the mid 1990s, a rapidly developing and often-fatal lung infection in the Southwestern United States was found to be caused by the Hanta virus that can be transmitted from rodents to humans. A final example is the viral zoonoses called West Nile virus. This virus, which can infect birds such as crows and blue jays, can be transmitted to humans by a mosquito that feeds on the bird and then subsequently feeds on a human.

There are a variety of zoonotic diseases that are caused by the movement of bacteria from an animal, bird, or insect host to humans. Examples include tularemia, which is caused by Francisella tulerensis, leptospirosis (Leptospiras spp.), Lyme disease (Borrelia burgdorferi), chlamydiosis (Chlamydia psittaci), salmonellosis (Salmonella spp.), brucellosis (Brucella melitensis, suis, and abortus), Q-fever (Coxiella burnetti), and campylobacteriosis (Campylobacter jejuni).

Fungi also produce zoonoses. An example is aspergillosis, which is caused by Aspergillus fumigatus.

Two protozoan zoonoses have emerged in accelerating numbers in the past two decades. One protozoan is called Giardia. The debilitating diarrhea that is commonly dubbed “beaver fever” is caused by drinking water that is contaminated with Giardia lamblia. Cryptosporidium parvum causes an equally debilitating diarrheal malady called cryptosporidiosis.

Giardia and Cryptosporidium live naturally in many wild animals. The loss of natural habitat with increasing human development has brought the animals and their microbial cargo into more frequent contact with people, and human infections are the result.

Human encroachment is also fueling the emergence of fatal viral hemorrhagic fevers such as Ebola and Rift Valley fever. The zoonotic origin of these agents is not definitively known. However, the available evidence strongly supports the idea that primate populations harbor the viruses, and that periodically transmission of the viruses from primates to humans occurs.

Beginning in 1986, an outbreak of bovine spongi-form encephalopathy (BSE) among cattle in the United Kingdom led to the eventual slaughter of over 150,000 domestic animals. Ominously, scientists have evidence that links the “mad cow” disease in the domestic animals with the brain degeneration in humans known as Creutzfeld-Jacob disease. There is the possibility that the disease-causing agent of Creutzfeld-Jacob disease was passed to some of the people when they ate infected beef.

Since the outbreak in the United Kingdom, BSE has been detected in cattle in both the United States and Canada on several different locations. The export of beef from Canada to the U.S. was halted in 2003 because of concerns for the saftety of U.S. cattle and beef-eating consumers. The ban was lifted in 2005.

The increasing incidence of these and other zoonotic diseases may be in part due to the increased ease of global travel. Microorganisms are global residents, which can easily move along with people and cargo. New combinations of microorganisms and susceptible human populations have and continue to arise.

Resources

BOOKS

Krauss, Hartmut. Zoonoses: Infectious Diseases Transmissible from Animals to Humans. Washington, DC: ASM Press, 2003.

Packer, Richard. The Politics of BSE. New York: Palgrave Macmillan, 2006.

Robinson, R. Veterinary Public Health and Control of Zoonoses in Developing Countries. Washington, DC: Food & Agriculture Organization of the United States, 2003.

Brian Hoyle