Abstract
During July and August 2001 the Minnesota Zoological Garden experienced an outbreak of proliferative dermatitis in three different ungulate species in three separate areas of the zoo. Nine musk oxen (Ovibos moshatus), eight Shetland sheep (Ovis aries) and two of four Sichuan takin (Budorcas taxicolor tibetana) were clinically affected. Disease severity and extent of lesions was markedly different between the affected species. However, histopathology and electron microscopy were consistent with a parapoxvirus infection in all individuals. Restriction enzyme analysis and partial gene sequencing of isolated virus suggest the outbreak was due to infection by a single orf virus (ORFV) strain.
Introduction
Orf (contagious ecthyma) is caused by a highly infectious epitheliotropic poxvirus of the genus Parapoxvirus which includes the closely related bovine papular stomatitis virus, pseudocowpox virus and parapoxvirus of red deer.3,4,10,11 Tentative members of the genus include Auzyk virus, chamois contagious ecthyma virus, red squirrelpox virus and sealpox virus.11 Orf virus has a worldwide distribution and is a common cause of disease in domestic sheep and goats and can affect a wide range of wild artiodactylids.11 Orf virus is readily transmitted to humans. Infection typically occurs when abraded skin contacts infected animals or fomites. Although there is no evidence for latent carriers of the disease,11 lesions can persist for months. In a dry environment at room temperature, ORFV is capable of surviving for 15 years.9
Case Report
On 28 July 2001, 8 of 9 (6.3) members of the musk ox (Ovibos moschatus) herd were observed with crusty lesions on their muzzles, lips or nostrils. The herd was comprised of animals ranging from 2 to 9 years of age. One bull, housed separately from the herd, was noted to have lesions on 2 August 2001. A quarantine area was established around the musk ox area and personnel caring for the animals wore protective clothing including coveralls, latex gloves, and rubber boots. Footbaths containing quaternary ammonia disinfectant (NPD Unicide 256, Brulin and Company, Inc., Indianapolis, IN 42606, USA) were utilized prior to leaving the area. Waste products from the animal enclosures were handled with separate equipment and taken to a separate compost area from that used for waste of other animals in the collection.
Animals developed multilobulated cauliflower-like papillomatous lesions on their muzzles and lips. Most also had proliferative lesions on the buccal aspect of oral mucous membranes. Severely affected animals had marked mucous membrane thickening and facial edema. Some animals had stertorous breathing due to partial occlusion of nares. Multilobulated, cauliflower-like, papillomatous lesions were noted around eyes and the tarsal and carpal joints of some animals. Diagnostic testing of biopsies confirmed parapoxvirus virus based on histopathology and electron microscopy. Older animals (greater than 5 years) were less severely affected and their lesions were significantly decreased within 1 month of onset of clinical signs.
Severely affected animals were given supportive medical care including some or all of the following throughout the course of the disease: intravenous fluids, penicillin G benzathine and penicillin G procaine (Crystiben, Fort Dodge, Fort Dodge, IA 50501, USA), ceftiofur sodium (Naxcel, Pharmacia & Upjohn Company, Kalamazoo, MI 49001, USA), B vitamins (Vitamin B Complex, Bimeda, Inc., Riverside, MO 64150, USA), flunixin meglumide (Banamine, Phoenix Pharmaceutical, Inc., St. Joseph, MO 64014, USA) iron dextran (Iron Dextran Injection, Durvet, Inc., Blue Springs, MO 64014, USA), stanozolol (Winstrol-V, Pharmacia and Upjohn Company) and dexamethasone sodium phosphate (Phoenix Pharmaceutical, Inc.). Lesions were cleaned topically with dilute povidone-iodine solution (Prodine Solution, Phoenix Pharmaceutical, Inc.) and lavaged with water from a garden hose. To reduce myiasis, animals were treated with permethrin pour on insecticides (Ultra Boss, Schering-Plough Animal Health Corp., Union, N.J. 07083 USA or Cylence, Bayer Corp., Shawnee Mission, KS 66201, USA) and pyrethrin/piperonyl butoxide fly gel (Pet-Guard, Virbac, Inc., Fort Worth, TX 76161, USA). Some of the animals became anorectic due to the severity of the disease. Even with supportive care, two animals died. A third severely affected animal was euthanatized 2 October 2001 due to its deteriorating condition.
All eight Shetland sheep (Ovis aries) housed at the zoo’s farm were observed with lesions on their lips on 16 August 2001. These animals were located approximately 160 meters from the nearest musk ox. These sheep were housed in the same building, but in separate pens from 39 pygmy goats (Capra hircus) and one Oberhasli goat (Capra hircus). Because of the zoonotic potential of the disease and to prevent transmission to other animals, the exhibit was immediately closed and all animals were moved to a quarantine area away from public contact. The sheep developed only mild, focal proliferative lesions on their lips. One of the sheep was euthanatized and submitted for necropsy; histopathology and electron microscopy of affected tissue confirmed parapoxvirus lesions. None of the goats developed any lesions. Lesions in the sheep resolved in about a month. However, the animals were not returned to the disinfected barn for 2 months to decrease the risk of transmission to zoo patrons.
On 26 August 2001, two of the zoo’s four Sichuan takin (Budorcas taxicolor tibetana) were observed to have “wart-like” lesions on their lower lips. These animals were housed at least 0.5 kilometers from either musk ox, or sheep exhibit areas. One of the affected animals was a 9-year-old cow with a nursing calf. The cow’s lesion did not become more severe and the calf never developed lesions. The other affected animal was a 16-month-old male. This animal developed multiple papillomatous lesions on its muzzle, nose, and oral mucous membranes; some of the lesions became ulcerated. Lesions were biopsied and electron microscopy of the fresh tissue revealed parapoxvirus. This animal continued to eat well and the lesions were nearly resolved a month later.
The first musk ox to die was markedly emaciated while the other two submitted for necropsy showed moderate emaciation. Gross skin lesions were previously described. The two animals, which died exhibited, moderate enlargement of retropharyngeal and submandibular lymph nodes. All three animals had acute moderate pulmonary congestion and acute diffuse alveolar pulmonary edema. The euthanatized musk ox had a solitary, approximately 2 cm diameter chronic ruminal ulcer. Lesions on the Shetland sheep were restricted to the lips.
Skin samples obtained from all affected species revealed similar histologic lesions that consisted of epidermal hyperplasia with marked ballooning degeneration of superficial keratinocytes; lymphoplasmacytic dermatitis and numerous bacterial colonies. In all cases superficial keratinocytes contained variable sized cytoplasmic eosinophilic inclusion bodies, which were consistent with Bollinger bodies. Electron microscopy of fresh samples of the affected epidermis confirmed the presence of characteristic ovoid-shaped parapoxvirus virions approximately 200 nm × 160 nm in all affected species. Confirmation of these results was done by amplification of parapoxvirus DNA by the polymerase chain reaction.
Virus isolation was performed on skin lesions from all species and virus was isolated from musk ox and Shetland sheep samples, but not from Sichuan takin samples. Lack of virus isolation in takin samples was likely due to small sample size.
Because all parapoxviruses have similar virion morphology, DNA characterization was performed to confirm that this disease outbreak was the result of an ORFV. Viral DNA collected from lesions of animals affected in this outbreak was compared to known strains of ORFV.2 By using a variety of techniques including DNA band pattern analysis and sequencing of particular genes, it was concluded that the proliferative dermatitis seen in the various ruminant species at the Minnesota Zoological Garden was caused by a single strain of ORFV.2
Discussion
An outbreak of orf affecting animals belonging to three ruminant species (musk oxen, sheep and takin) is described. The occurrence of this outbreak during summer likely made disease control and supportive care of the animals more difficult due to myiasis and flies acting as potential mechanical vectors for the virus. This might account for the spread of the disease to different locations within the zoo as zoo personnel immediately implemented protocols, described previously, to control spread of the disease. The hot summer weather increased the risk of animals becoming hyperthermic while being immobilized for supportive care. Unfortunately, the long duration and severity of lesions caused anorexia and secondary bacterial infection, which contributed to the decline of the animals. Cidofovir (Vistide, Gilead Sciences, Foster City, CA 94404, USA) has shown marked in vitro inhibitory effects for parapoxviruses and may be useful as a treatment for ORFV infected animals in the future.8
The source of the ORFV in the outbreak reported here could not be determined although several possibilities exist. In 2000, the zoo opened a working farm that exhibits dairy cattle, sheep, goats, pigs, draft horses, poultry and rabbits. All animals acquired by the zoo are isolated from other animals during a quarantine period of at least 30 days. During this time animals are examined for evidence of health problems and communicable diseases and are not allowed to enter the collection if diseases are detected. No evidence of orf-like lesions had been seen in these domestic animals during quarantine or at any time since the farm exhibit opened. Although there is no evidence of latent virus infection in animals recovered from ORFV11 it is possible some of the small ruminants recently introduced to the farm may have acted as physical carriers of the virus. Animal caretakers or visitors to the zoo could also have carried the virus into the zoo on clothing.
The zoo is located adjacent to a nearly 2000-acre county park, which contains numerous white-tailed deer (Odocoileus virginianus). Orf has not been reported in wild white-tailed deer; however, experimental exposure did cause clinical disease.6 Although the suburbs have taken over the agriculture land which surrounded the zoo when it opened in 1978, in 2001 residents remained within a few miles of the zoo who had horses and quite likely sheep or goats. Therefore, the possibility that dry scab from affected wildlife or livestock in nearby areas was blown by the wind onto zoo premises cannot be eliminated as the potential source of this outbreak. The virus can survive for years in dry scab7,9 and a remote possibility exists that it survived in a protected location within the musk ox exhibit since an outbreak occurred at the Minnesota Zoological Garden in September 1983. That outbreak was confined entirely to the musk ox herd and eight of the twelve animals in the herd were noted to have lesions.12
Although orf is a relatively common disease in sheep and has been reported in musk oxen,1,5,12 this is the first reported case of orf in Sichuan takin. The introduction of ORFV (Parapoxvirus ovis) into a zoo creates a considerable risk for various ruminant species and visitors. As the present report shows, the range of ruminant species known to be susceptible to ORFV is growing and possibly all nondomestic ruminant species should be considered susceptible to the disease.
Literature Cited
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