Zoonotic diseases of sheep and goats (Proceedings)

Article

Many sheep and goat producers are unaware of zoonotic diseases that can be passed from animals to man. Some zoonoses such as pinkeye or soremouth cause symptoms in the host animal so that the producer knows the animal is ill, but he may not realize that the disease could be transmitted to himself or his family.

Many sheep and goat producers are unaware of zoonotic diseases that can be passed from animals to man. Some zoonoses such as pinkeye or soremouth cause symptoms in the host animal so that the producer knows the animal is ill, but he may not realize that the disease could be transmitted to himself or his family. Other zoonotic diseases such as campylobacter enteritis or Q fever often do not cause symptoms in sheep or goats and the producer may not take adequate precautions to prevent transmission. Some zoonoses are transmitted directly from the animal to producer, while others are passed indirectly through fomites such as milk, meat, or fiber.

Rabies

The incidence of rabies has steadily risen in the United States over the past few years due to epizootics in raccoons, skunks, foxes and coyotes. In 2001, 322 cases of rabies were diagnosed in California including one cat, one horse, 151 skunks, 2 foxes, 166 bats and 1 human. Between January and September 2008, there were 18 confirmed cases of rabies in skunks in Colorado when historically there have not been any cases of terrestrial rabies in that state. The DNA type of the virus involved in these skunk rabies cases indicated that they originated in Texas. Recently 24 dogs and cats adopted by soldiers in Iraq entered the United States without proper proof of rabies vaccination and at least one dog in that shipment died of rabies after importation. As the incidence of rabies in wild life has increased, the number of documented cases of rabies in sheep and goats has also risen and this has lead to an increased exposure for humans. In 1996, a rabid goat at a New York County Fair exposed more than 2700 people, and more than 400 people received prophylaxis at a cost exceeding $1000 per person.

Public health officials stress the need to vaccinate domestic pets and livestock against rabies to provide a safety barrier between wild animals and man. There are currently four rabies vaccines licensed and labeled for use in sheep, but no vaccines are labeled for use in goats or camelids in this country. Each state veterinarian is responsible for determining what regulations apply for species for which there is no legal vaccine. Some state veterinarians have ruled that exhibited goats must be vaccinated, while others require exposed animals to be euthanized and tested for rabies. The CDC Compendium of Animal Rabies Prevention and Control recommends that all animals in petting zoos or for exhibition be vaccinated for rabies.

Reports of rabies in goats are rare, but the furious form of rabies appears to be more common. Symptoms in goats include aggressive behavior, excessive bleating, and salivation following an incubation period of one to five days. Cases of rabies in sheep appear more similar to rabies in cattle with an average incubation period of ten days. Rabid sheep exhibit muzzle and head tremors, aggressiveness, hyperexcitability, hyperesthesia, salivation, vocalization and recumbancy. There is no treatment for rabies in animals and treatment for exposed humans must be undertaken before clinical symptoms appear. With only one exception, all cases of rabies are fatal once clinical symptoms develop. When examining a sheep or goat with neurologic symptoms, remember that the affected animal might have rabies and wear disposable gloves to examine the oral cavity.

Campylobacteriosis

Campylobacter jejuni is the most common cause of food-borne illness in man and there are more cases of campylobacteriosis diagnosed each year than those of shigella and salmonella combined. One study revealed that approximately 45% of fecal samples from normal sheep and goats contained C. jejuni. The organism can be transmitted through fecal contamination of milk or by handling aborted fetuses and membranes. Many human outbreaks with sudden onset of severe nausea, cramps, vomiting, and fluid diarrhea have been traced to consumption of raw goat milk. Human infection with this organism can lead to Guillan Barre Syndrome, and pregnant women should not have contact with aborting sheep or goats. Food-borne illness caused by campylobacter is usually prevented through washing hands, wearing disposable gloves when handling aborted fetuses or membranes, and consuming only pasteurized milk and dairy products. Transmission of Campylobacter from animal to man can be reduced through improving sanitation of the sheep or goats. Clipping the hair on the udder and belly of lactating animals, frequent cleaning of the animal housing, thorough cleaning of the teats prior to milking, and use of pre-milking iodine dip help reduce transmission of this bacteria through milk. Use of disposable gloves and face masks during pen cleaning and assistance with birthing also reduces transmission of this agent. Herds that experience abortion due to Campylobacter jejuni should vaccinate prior to breeding, and there is anecdotal evidence that feeding chlortetracycline to pregnant sheep and goats may decrease the incidence of abortion due to this microbe.

Chlamydophila

Chlamydophila abortus (formerly Chlamydia psittaci) travels through most small ruminant herds sooner or later, especially in herds that show or purchase new stock. Symptoms of chlamydophila in both small ruminants and humans include pinkeye, pneumonia, polyarthritis, and/or abortion. Naive stock may develop pinkeye during the spring, summer or fall with abortions developing in the bred females the following spring. Affected animals may remain asymptomatic carriers for several months to years following infection and can transmit the disease to other herds through direct contact. Affected males and those that have apparently recovered can transmit chlamydophila during breeding. Producers treating conjunctivitis should wear plastic gloves and wash their hands thoroughly afterwards. Disposable plastic gloves should always be worn when assisting with birth, handling aborted fetuses and removing placental membranes. Pregnant women should not work with sheep or goats during an abortion storm. Veterinarians screening show animals should not allow sheep or goats with pinkeye to be exhibited at shows or fairs. Occasionally fairs allow display of pregnant animals to demonstrate normal parturition, and a barrier should be placed between the animals and the observers to prevent public contact with the birthing fluids, membranes and neonates. A commercial vaccine is available for prevention of chlamydophila abortion and it should be administered to both males and females prior to breeding. Anecdotal evidence suggests that feeding chlortetracycline to pregnant sheep and goats in the last 60 days of gestation will decrease the incidence of abortion due to this organism.

Toxoplasmosis

Although toxoplasmosis is more commonly associated with cat feces, Toxoplasma gondii is an important cause of abortion in sheep and goats. Transmission to man has been documented from both meat and milk, and there is risk to pregnant women from exposure to aborted fetuses and membranes. Early prenatal infection in women without previous exposure to Toxoplasma may lead to fetal death while infection later in the pregnancy is associated with chorioretinitis, brain damage, hepatomegaly, splenomegaly, and fever, jaundice and convulsions at birth. Because part of the toxoplasma life cycle must take place in the digestive tract of young cats, all farm cats should be neutered and fed well to maintain a healthy feral population that will kill vermin. Well-fed cats kill more mice and rats than hungry cats, and they are much healthier and live longer. Because cats like to use grain as cat litter, all grain should be well covered to prevent this use. Consumption of thoroughly cooked meat and pasteurized milk, wearing protective gloves and face masks, and good sanitation help prevent toxoplasmosis in humans.

Q fever

In humans, Q fever, or infection with the rickettsia Coxiella burnetii, may be evidenced by chills, severe headache behind the eyes, weakness, malaise and night sweats. There is a great deal of variation in severity and duration of symptoms in man, but few sheep or goats develop clinical disease other than occasional abortion. Small ruminants may transmit the rickettsia in their wool, urine, feces, blood, placental membranes, and aborted fetuses. Aerosol transmission may occur when cleaning barns, during slaughter or when performing a cesarean section, so face masks, protective clothing and gloves should be worn for these procedures. Pregnant women should not have contact with parturition in sheep or goats. This organism spreads readily in the wind, and human cases have occurred even up to a mile away from the infected sheep or goats.

Soremouth

Soremouth or contagious ecthyma is caused by infection with a parapox virus and commonly presents as crusts around the nose and lips of young lambs and kids that interfere with feeding and slow growth rates. Lesions may also occur on the teats and udders of does or ewes nursing affected young stock and may be a source of infection for producers that hand milk their goats. Less commonly, soremouth may appear as crusts and grey scurf near the hooves at the coronary band. Producers administering the live-virus vaccine or handling lambs and kids with crusts may develop blisters on their hands that progress to welts and raised painful plaques. Occasional producers have developed severe, life-threatening pneumonia when diseased young cough virus in their faces. Producers handling affected young or using live virus vaccine should wear gloves and face masks, and they should keep the reconstituted vaccine away from eyes, face, mouth and hands.

Ringworm

Fungal skin infections occur commonly in show lambs during the late spring and summer months due to frequent short clipping and repeated bathing prior to shows. Ringworm is less common in goats unless they are exposed to sheep or their hair is clipped very short and they are bathed frequently. Classically, ringworm presents as round lesions with alopecia, scaling, erythema, and crusts, but a form in lambs known as club lamb fungus may exhibit raised thick plaques often about the ears, head and neck. Ringworm is readily transmitted to man, so producers treating affected animals should wear plastic gloves and wash their hands thoroughly afterwards. Veterinarians working at shows should not allow animals with ringworm to be exhibited. A variety of disinfectants including chlorhexidine, sodium hypochlorite, iodophors and benzalkonium chloride and garden fungicides such as captan have been used with varying degrees of success in treating livestock cases of ringworm.

Anthrax

Wool-sorter's disease, or cutaneous anthrax as evidenced by development of a depressed black eschar, occurs occasionally in people handling contaminated wool, carcasses and goatskins or hides. Most human infections have been traced to imported products. When anthrax is suspected as a cause of sudden death in livestock, diagnosis should be based on smears of aspirated blood or lymph nodes not necropsy, and anthrax carcasses should be buried or burned but not rendered.

Less common zoonoses: Listeriosis, salmonellosis, brucellosis, parasites

Outbreaks of listeriosis, salmonellosis and brucellosis have been traced to consumption of raw milk and dairy products or exposure to carcasses during slaughter. Salmonella have also been implicated in human cases associated with outbreaks of diarrhea in feedlot lambs. There are distinct regional differences in the incidence of these diseases in sheep and goats in this country. Human listeriosis may be associated with abortion or acute meningitis as evidenced by sudden onset of fever, intense headache, nausea, and vomiting leading to delirium and coma. The most common clinical presentation of human salmonellosis is acute onset of gastroenteritis with fever, abdominal pain, diarrhea, nausea and vomiting. Brucellosis associated with sheep and goats is extremely rare in this country but would be characterized by insidious onset of intermittent fever of variable duration, headache, weakness, profuse sweating, chills, arthralgia, and general malaise. Two parasites, Cryptosporidia and Echinococcus granulosa, occasionally infect small ruminants and can be transmitted to man through fecal contamination. Hydatid disease of man is caused by space-occupying tapeworm cysts of Echinococcus that are perpetuated by a life cycle of dog feces contaminating grass, sheep eating the parasites on grass and then dogs eating sheep offal. In order to prevent transmission of Echinococcus, dogs should not be allowed to eat sheep offal or raw meat from sheep. Good hygiene with frequent hand washing and consumption of thoroughly cooked meat and properly pasteurized dairy products remain the best prevention for all of these diseases.

Johne's disease

Johne's disease or infection with Mycobacterium avium paratuberculosis is an important cause of chronic weight loss and unresponsive diarrhea in both wild and domestic ruminants. While Johne's disease is not currently classified as a zoonotic disease, there is increasing evidence that MAP may be associated with Crohn's disease in man. MAP can be found in many ruminant tissues such as the uterus, muscle and lymph nodes as well as in milk and feces. Infected sheep and goats shed large numbers of bacteria in their colostrum, milk and feces which then heavily contaminate the environment. Producers should use good sanitation and sound milking practices to prevent fecal contamination of harvested milk, and all milk should be pasteurized prior to consumption. Frequent hand washing, consumption of thoroughly cooked meat and proper pasteurization of dairy products may decrease transmission of MAP from animal to man.

3Healthy, vigorous producers and veterinarians may not demonstrate symptoms of many of these zoonotic diseases. Most zoonotic diseases are more severe in infants, immune-suppressed individuals and aged, debilitated adults. Those individuals taking immune-suppressive drugs or affected with immune-suppressing diseases such as leukemia or HIV may die of zoonotic disease. Cleanliness, sanitation, vaccination, use of protective gloves and face masks, and proper cooking and handling of food can prevent transmission of these diseases from sheep and goats to man.

Further Reading

Heymann, D. L. (ed.) (2004). Control of Communicable Diseases Manual (18th edn). Washington D. C.: American Public Health Association.

Kahn, C. M. (ed.) (2005). The Merck Veterinary Manual (9th edn.). Whitehouse Station: Merck & Company.

National Association of State Public Health Veterinarians. (2008) Compendium of Animal Rabies Prevention and Control, 2008. MMWR. 57(RR02):1-9.

Pugh, D. G. (ed.) (2002). Sheep and Goat Medicine. Philadelphia: W. B. Saunders Co.

Radostits, O. M., Gay, C. C., Blood, D. C. and Hinchcliff, K. W. (2000). Veterinary Medicine A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses (9th edn.). London: W. B. Saunders Co.

Smith, M. C. and Sherman, D. M. (1994). Goat Medicine. Philadelphia: Lea & Febiger.

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