ASI provides update on zoonotic diseases in sheep and goats

Lambing season is one of the busiest times of the year, and as producers prepare for the birth of new lambs, it is a good time to discuss zoonotic diseases. 

On the March 12 episode of the American Sheep Industry (ASI) podcast, Host Jake Thorne, sheep and goat program specialist at Texas A&M AgriLife Extension, spoke with Animal Health Committee Co-Chair Dr. Cindy Wolf about zoonotic diseases of sheep and goats.

According to the U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS), zoonotic diseases are contagious diseases and can be spread between animals and humans. 

“It is estimated approximately 75 percent of recently emerging infectious diseases affecting humans are diseases of animal origin, where approximately 60 percent of all human pathogens are zoonotic,” reads the USDA APHIS website.

Humans can contract zoonotic diseases through direct contact with infected animals, by consuming contaminated food or water, inhalation, arthropod vectors and pests.

“Of the infectious diseases diagnosed in people, six out of every 10 are known as diseases coming from animals,” Wolf says. “It’s not a scary thing – it’s just good to be aware of.”

She adds national statistics are showing an increase in zoonotic diseases, but this could be due to the fact testing and surveillance for the diseases have improved over the years as well. 

Zoonotic diseases

“With zoonotic diseases, the transfer of disease from animals to humans is more common with reptiles, dairy calves and poultry,” Wolf explains. 

Chlamydia abortus and Campylobacter fetus are two bacteria that cause abortions in sheep and goats and can potentially be zoonotic, Wolf reports.

Chlamydia abortus infects sheep and goats. They will often show little to no symptoms when they first become infected.

The only sign of disease is the birth of weak or stillborn lambs in the last two to three weeks of pregnancy.

“Bacteria infect the uterus and is present in the afterbirth of infected animals,” she notes. “If producers experience losses a couple weeks prior to the due date of lambing, they should call their veterinarian.”

Biosecurity

Producers should always have a good biosecurity regimen in place to improve farm efficiency, protect neighbors and safeguard animal and human health.

Wolf says, “Biosecurity is not just to protect farm animals, it is also to protect the producer, their families and farmworkers.”

Disease is not always apparent, especially in early stages, so anyone visiting a farm who is not abiding by biosecurity measures can run the risk of spreading diseases to and from the premises.

She recommends removing boots prior to entering the house and washing hands for 20 seconds with soap and water to reduce the spread of zoonotic diseases. If a producer is out in the field, they should use a hand sanitizer with 60 percent alcohol.

Caseous lymphadenitis

This zoonotic disease poses significant economic losses to livestock industries due to various factors such as decreased marketability of breeding stock, condemnation of carcasses and animal death.

Caseous lymphadenitis (CL) is a bacterial infection caused by Corynebacterium pseudotuberculosis resulting in superficial or internal abscesses and recurrent development of abscesses. 

“CL is spread primarily through contact with material from abscesses or contaminated with abscess material, such as during shearing,” Wolf notes.

When abscesses are present in the lungs, CL was transmitted through respiratory secretions, including nasal discharge or coughing. 

The bacteria can persist in contaminated soil for up to two years, making transmission possible through contact with contaminated equipment, facilities, pastures and feed and water troughs. 

She remarks, “Herd mates can also spread the disease when they come into direct contact with a ruptured abscess, so it’s important to note CL-infected animals can carry the disease for life.”

According to Wolf, there is no cure for CL, so producers should implement management practices to minimize its impact.

Johne’s disease

Wolf continues her discussion by explaining Johne’s disease, a contagious, chronic and usually fatal infection which primarily affects the small intestine of ruminants, caused by Mycobacterium avium subspecies paratuberculosis.

“In cattle, signs of Johne’s disease include weight loss and diarrhea with normal appetite. Several weeks after the onset of diarrhea, a soft swelling may occur under the jaw, but in sheep and goats, the clinical signs are harder to spot,” she says. 

“Affected sheep continue to eat but lose weight and waste away,” she adds. “Although the disease causes diarrhea in cattle, less than 20 percent of sheep show diarrhea symptoms.”

Johne’s is very stable in the environment, and in favorable conditions, can live outside of the host animal for an extended period of time.

Due to a long incubation period, most infected sheep do not show signs of the disease until later in life, possibly infecting younger sheep and lambs.

Additional diseases

Club lamb fungus affects the skin of sheep and is also known as sheep ringworm. This disease got its name because it most commonly affects show lambs. It is a highly contagious disease, which can be contracted by humans, according to Wolf.

“Good hygiene and management practices are critical to the prevention of club lamb fungus,” she says. “Careful shearing to avoid nicks and cuts and less frequent shampooing and grooming will help promote healthy skin, reducing the incidence of disease. Avoiding crowded and humid environments is also beneficial.”

She mentions sore mouth, often known as orf, contagious ecthyma or scabby mouth, is a viral infection primarily of sheep and goats and the condition is caused by a poxvirus called orf virus.

Shepherds, veterinarians and producers handling sheep or goats can contract orf from an infected animal or equipment.

Individuals can develop painful sores on their hands, which can last for two months and infected individuals rarely infect others.

Wolf closes the podcast discussing future research needs, as efforts to develop and implement vaccine interventions to reduce zoonotic disease is limited.

Melissa Anderson is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.