Zoonoses are diseases that are naturally transmitted between animals and humans. The following are major zoonoses that can be transmitted from commonly used laboratory animals to humans.
Bacterial enteric diseases—Campylobacteriosis, Salmonellosis, and Shigellosis
- Campylobacteriosis and Salmonellosis
These two diseases are caused by bacterial organisms commonly found in many species of animals including some laboratory rodents, chickens, reptiles, cats, dogs, ferrets, rabbits, sheep, pigs and nonhuman primates. Rats and guinea pigs are especially susceptible to Salmonella infection. According to the Centers for Disease Control and Prevention, Campylobacter is the most common cause of bacterial diarrheal illness in humans in the United States. Fecal-oral is the primary route of transmission between animals and from animals to people. Animals are often asymptomatic carriers of these organisms, acting as a source of infection but not demonstrating any clinical signs themselves. Signs in infected humans are characteristic of acute gastrointestinal disease including diarrhea, dehydration, nausea, fever and abdominal cramping.
Shigella is a bacterial organism which commonly infects primates. People are the primary reservoir of the disease. Nonhuman primates contract the disease via exposure to other primates. They can be asymptomatic or have diarrheal illness that may result in death. People become infected by ingestion of fecal contaminated food or water, or by direct contact with infected animals. Humans usually have mild diarrhea although more severe signs such as dysentery (mucus and blood in feces), anorexia, weight loss, abdominal pain and death are possible.
- Protozoal enteric diseases—Giardiasis and Amebiasis
This is an intestinal disease caused by the protozoan parasite, Giardia spp. The organism is found in the feces of many species of animals including dogs, cats, rodents and nonhuman primates. The common mode of transmission is by ingestion of fecal contaminated food or water. Both infected humans and animals may show no signs at all, or develop illness characterized by diarrhea, abdominal pain, anorexia, lethargy and weight loss.
The protozoan, Entamoeba histolytica, is the agent of amebiasis also known as amebic dysentery. This organism is carried by nonhuman primates. It is shed in the feces and infected cysts can persist in the environment for up to one month. Transmission occurs via the fecal-oral route or ingestion material contaminated by infected cysts. Humans can be asymptomatic or demonstrate gastrointestinal symptoms (watery diarrhea, abdominal discomfort and dysentery with malaise). These clinical signs can wax and wane over a period of years.
This disease is caused by Brucella spp., bacterial organisms present in dogs, sheep, cattle pigs and goats. The route of infection in humans in the laboratory animal facility can be contamination of wounds and mucous membranes, and inhalation of Brucella containing aerosols. The bacteria disseminate through the body via the bloodstream and eventually enter the lymphatic system. Symptoms in infected people include fever, chills, sweats, weakness, generalized aches and weight loss. Without treatment, the disease can progress to include emotional and cardiac signs and arthritis. These symptoms can wax and wane over a period of years.
Cat Scratch Disease (CSD)
This infection is caused by Bartonella henselae, a bacterial organism. The common mode of transmission is by scratches or bites of cats and dogs. It is believed that the cat flea sheds this organism and plays a role in spread of disease between cats and from cats to humans. Symptoms of infection in people include a red blister at the inoculation site, swollen lymph nodes, malaise, fever and nausea.
Cercopithecine herpesvirus I
Cercopithecine herpesvirus I (formerly Herpesvirus simiae or B-virus) is found most commonly in Old World monkeys as a latent infection and is especially prevalent in macaque monkeys. The virus is transmitted from monkeys to people primarily by means of bites and scratches and through contact of infected body fluids with broken skin. A splash to the eye has also been recognized as the cause of fatal infection. Infected people demonstrate severe neurologic signs with a 70% fatality rate. Although the risk of acquiring a B-virus infection from macaques is very low, the seriousness of this disease warrants extreme care when handling macaques.
Contagious Ecthyma (Orf)
Orf virus causes disease in sheep and goats characterized by pustular and necrotic lesions on the lips, gums, nostrils, urogenital orifices, teats and udders. Orf is transmitted to people by direct contact with lesions and exudates containing virus. Symptoms in people include solitary or multiple lesions on the hands, arms or face, which are pustular and eventually begin to weep.
This group of fevers (Yellow Fever, Dengue, Marburg Virus, Ebola, Hantavirus) is caused by RNA viruses. Transmission is via direct contact with infected animals, exposure to blood and/or body excretions of infected animals, fomites (e.g., contaminated medical sharps) or arthropod insect bites. Symptoms include fever, bleeding from multiple areas of the body, low blood pressure and shock. Infections with Hantavirus, Ebola virus and Marburg virus are associated with a high fatality rate.
Hemorrhagic Fever with Renal Syndrome (HFRS);
Hantavirus Pulmonary Syndrome
A variety of rodents carry hantaviruses which can result in human disease. Infection can occur following brief exposure. Transmission is usually by inhalation of contaminated aerosols, but spread via animal bites and contaminated cell lines is also possible. Illness in humans is characterized by flu like symptoms which can progress to kidney and/or respiratory failure, hemorrhage and death. This disease is rarely observed in barrier-reared rodents; however, because it is such a severe disease it should be considered.
Infections from Dog or Cat Bites
Two common bacterial organisms that can infect bite wounds are Pasteurella multocida and Capnocytophaga canimorsus. Both bacteria are present in the normal oral flora of dogs and cats. Signs can vary from a localized cellulitis or abscess to septicemia (fever, chills, malaise, vomiting and diarrhea, gangrene and seizures). C. canimorsus commonly infects immunocompromised individuals, with a 33% fatality rate.
The influenza virus infects a number of animal species including humans, birds, ferrets, horses and pigs. Transmission is caused by aerosol exposure. The risk of humans acquiring the virus from animals is low. The virus causes an acute disease characterized by upper respiratory and gastrointestinal symptoms with fever. Ferrets and rodents can be susceptible to infection from humans.
Lymphocytic Choriomeningitis (LCM)
LCM is caused by a virus carried by rodents. The virus causes minimal clinical signs in rodents. Transmission is via bite wounds or inhalation of contaminated air or exposure to contaminated cell lines. Flu like symptoms are usually observed in infected humans, but more severe manifestations of disease such as encephalomeningitis and death can occur.
This bacterial disease is caused by Pasteurella organisms. Many animals including, dogs, cats, rabbits, ruminants and birds carry these bacteria. Pasteurella is primarily spread by bites and scratches and is especially threatening to immunocompromised people. Symptoms in people include abscess formation at the site of the bite or scratch, and respiratory, bone or joint infections.
Pneumocystis carinii has been generally classified as a protozoan, but recent evidence suggests that it may be a fungus. Most animal species harbor this organism in the respiratory tract. Pneumocystis is primarily transmitted via inhalation and does not cause clinical signs in immunocompetent animals or people. Infected immunocompromised individuals develop anorexia, weight loss and pneumonia.
Q Fever is transmitted by Coxiella burnetii, a bacteria that commonly infects sheep, goats and cattle. The organism is shed in the placental tissues, urine, feces, milk and blood of these animals. The primary mode of transmission is via inhalation of infectious aerosols. Coxiella burnetii is highly infectious and resistant in the environment. Infected animals are usually asymptomatic. Symptoms of infection in people include acute onset of flu like illness characterized by fever, headache, chills, sweats and weakness as well as a nonproductive cough and pneumonia. Serious sequellae include endocarditis, hepatitis and nephritis.
All mammals are susceptible to the rabies virus, which is almost always fatal in people. Transmission is usually through exposure to the body fluids of an infected animal, primarily via bites. Aerosol transmission is possible in specialized conditions such as laboratory settings and bat caves. Clinical signs in infected humans include fever, malaise, salivation and behavioral changes which can progress to paresis, paralysis, convulsions and coma.
Rat Bite Fever (RBF)
This disease is caused by one of two bacteria (Streptobacillus moniliformis or Spirillum minus) that inhabit the oral cavity of rats. It is spread by bite wounds. Although the rats show no signs, infected people display swelling at the bite wound, flu-like symptoms and enlarged lymph nodes.
This is a fungal infection of the skin that can be transmitted by contact with infected animals or contaminated bedding, caging etc. Many mammals including rodents, rabbits, ferrets, dogs, cats, pigs, ruminants and nonhuman primates can carry one of the fungal organisms (dermatophytes), which cause ringworm. Crusty lesions may be evident in animals. Infected people develop flat spreading, ring-shaped skin lesions which may or may not be itchy. This is not a serious disease and is often self-limiting.
This tropical nematode parasite Stronglyloides can infect dogs, cats, nonhuman primates and swine. It is transmitted via penetration of the infective larvae through the skin. Infected humans demonstrate skin lesions, urticaria, cough (due to pulmonary migration) and gastrointestinal signs.
The neurotoxin of the bacterium, Clostridium tetani, can cause tetanus in many animal species. People are infected by the bite or scratch of an infected animal or bacterial inoculation of a wound contaminated with soil or intestinal flora of herbivores. Symptoms of infection in people include painful spasms of the cheek and neck muscles (lock jaw), exaggerated reflexes, abdominal muscle tightening, convulsions and death.
Toxoplasmosis is caused by an intracellular coccidian parasite (Toxoplasma gondii) that resides in most warm-blooded animals. The domestic cat is the primary reservoir for transmission of infection to humans in the laboratory animal facility. Infection in the lab can occur by handling the feces of infected cats. Signs in immunocompetent humans are usually subclinical, but flu like symptoms are possible. Pregnant women are at risk for having abortions, stillbirths or birth defects.
Endoparasites of the genus Trichuris are commonly known as whipworms. The species of whipworm in nonhuman primates has zoonotic potential. It is transmitted in feces and is characterized by gastrointestinal disease in people.
Tuberculosis (TB) and Other Mycobacterial Infections
Tuberculosis is caused by the bacterium, Mycobacterium tuberuclosis. Cattle, humans and birds are considered the major reservoir hosts. Many animals (e.g., birds, nonhuman primates, pigs, sheep, goats, cattle, dogs, cats and ferrets) are susceptible. Transmission among animals including people is primarily by inhalation. Two forms of clinical disease can occur in infected humans: the pulmonary form and the extrapulmonary form. The former is characterized by a productive cough, fever, lethargy, anorexia, weight loss and coughing up blood. The extrapulmonary form can cause enlarged lymph nodes, meningitis, bone infection and inflammation around the heart.
Other species of Mycobacterium harbored in various animals can result in human infection. Fish and amphibians have been known to transmit atypical Mycobacteriosis to humans causing "fish handler's granulomas" or "aquarist's nodules." More serious manifestations include osteomyelitis and tenosynovitis. Immunocompromised people are especially at risk.