Contagious Ecthyma (Orf Virus Infection) in Sheep and Goats

Contagious ecthyma, also known as orf, is a highly contagious, zoonotic, pustular dermatitis caused by the orf virus (ORFV), a member of the genus Parapoxvirus within the family Poxviridae. The disease primarily affects sheep and goats of all ages, but is most commonly seen in lambs and kids, particularly those aged 3 to 6 months. It is characterized by proliferative, scabby, and sometimes ulcerative lesions on the lips, muzzle, oral mucosa, and less frequently on the udder, teats, and feet. In adult ewes and does, lesions may appear on the udder and teats, leading to mastitis and reluctance to nurse offspring. The disease is endemic in most sheep and goat producing regions worldwide, causing significant economic losses due to reduced weight gain, secondary bacterial infections, mastitis, and occasional mortality in severe cases. The virus is highly resistant in the environment, surviving for months in dried scabs, facilitating transmission. Although usually self-limiting, orf can be severe in immunocompromised animals and humans, where it causes painful nodular lesions on the hands. The disease is of considerable public health importance due to its zoonotic potential, particularly among farmers, veterinarians, and abattoir workers. In flocks, orf can cause outbreaks with high morbidity (up to 90%) but low mortality (usually less than 1%), unless complicated by secondary infections or myiasis. The disease is also known as scabby mouth, sore mouth, or contagious pustular dermatitis.

The causative agent is the orf virus (ORFV), a double-stranded DNA virus belonging to the genus Parapoxvirus, family Poxviridae. Other parapoxviruses include bovine papular stomatitis virus and pseudocowpox virus, but ORFV is the primary pathogen in sheep and goats. The virus is epitheliotropic, replicating in regenerating epidermal cells, and is characterized by a unique ability to evade the host immune response through the production of immunomodulatory proteins, such as a viral interleukin-10 homologue and a vascular endothelial growth factor (VEGF) homologue, which contribute to the proliferative nature of the lesions. The virus is highly resistant to environmental degradation, surviving in dried scabs for months to years, and is resistant to many disinfectants, though it is inactivated by heat (56°C for 30 minutes) and certain lipid solvents. There is only one serotype of ORFV, but genetic variability exists among strains, which may influence virulence and cross-protection. The virus is transmitted by direct contact with infected animals or contaminated fomites, including feeding troughs, waterers, and handling equipment. The virus enters through broken skin or mucous membranes, often via minor abrasions on the lips or mouth during nursing or grazing. The incubation period is typically 2 to 7 days. The virus does not cause systemic viremia; lesions remain localized to the skin and oral mucosa. The disease is self-limiting, with lesions resolving in 3 to 4 weeks, but the virus can persist in the environment and in carrier animals, leading to recurrent outbreaks.

Contagious ecthyma is distributed worldwide, with a higher prevalence in temperate and Mediterranean climates. It affects both sheep and goats, but goats may exhibit more severe and prolonged lesions. All ages are susceptible, but lambs and kids aged 3 to 6 months are most commonly affected, likely due to waning maternal immunity and increased exposure during weaning. Outbreaks are more frequent in intensive production systems, such as feedlots and dairy goat operations, where animals are closely confined and fomite transmission is facilitated. The disease is also common in range flocks, particularly during lambing season when animals are gathered for processing. Morbidity can reach 90% in naive flocks, while mortality is usually low (<1%), but can be higher in young animals with secondary bacterial infections or when lesions affect the oral cavity, preventing feeding. The virus is maintained in the environment through contaminated scabs, which can remain infectious for years, and in carrier animals that may shed the virus intermittently. The disease is more prevalent in the spring and summer months, possibly due to increased contact during lambing and grazing on abrasive vegetation. Economic losses arise from reduced weight gain, treatment costs, mastitis in ewes, and culling of affected animals. The zoonotic potential is significant, with human infections occurring through direct contact with lesions or contaminated fomites, particularly in individuals with compromised skin integrity. The disease is often underreported due to its self-limiting nature, but it is a major concern for small ruminant producers and public health authorities.

The orf virus enters through breaks in the skin or mucous membranes, typically on the lips, muzzle, or oral cavity. The virus replicates in the cytoplasm of epidermal cells, particularly keratinocytes, causing cell proliferation and degeneration. The viral VEGF homologue promotes angiogenesis and epidermal hyperplasia, leading to the characteristic proliferative, scabby lesions. The virus also encodes immunomodulatory proteins that suppress the host's innate and adaptive immune responses, allowing the virus to persist and replicate. The lesions progress through stages: erythema, papule, vesicle, pustule, and scab formation. The scabs contain high concentrations of infectious virus and are shed into the environment, contaminating pastures and facilities. The virus does not cause systemic infection, but secondary bacterial infections, such as Staphylococcus aureus, Streptococcus spp., and Fusobacterium necrophorum, can complicate the lesions, leading to deeper tissue damage, abscessation, and in severe cases, septicemia. In lactating ewes and does, lesions on the udder and teats can lead to mastitis, which may be clinical or subclinical, reducing milk production and increasing the risk of transmission to nursing offspring. The disease can also affect the feet, causing lameness. The immune response to ORFV involves both humoral and cell-mediated immunity, but the virus has evolved mechanisms to evade immune clearance, resulting in incomplete protection and the possibility of reinfection. The proliferative nature of the lesions is due to the viral VEGF, which stimulates endothelial cell proliferation and vascular permeability, leading to the characteristic raised, wart-like appearance.

Several factors predispose sheep and goats to contagious ecthyma. Young animals, particularly those aged 3 to 6 months, are more susceptible due to waning maternal immunity and increased exposure during weaning. Stressful conditions, such as poor nutrition, overcrowding, and concurrent infections, can increase susceptibility and severity. The virus is more likely to cause outbreaks in intensive production systems where animals are closely confined and fomite transmission is common. Abrasions on the lips and mouth, which can occur from grazing on rough vegetation, feeding on thorny plants, or using abrasive feeding equipment, facilitate viral entry. The presence of the virus in the environment, particularly in dried scabs, is a major risk factor for outbreaks. The disease is more common in the spring and summer months, possibly due to increased contact during lambing and grazing on abrasive vegetation. Poor biosecurity practices, such as introducing new animals without quarantine, can introduce the virus into naive flocks. The use of contaminated equipment, such as ear taggers, shearing equipment, and feeding troughs, can also spread the virus. In dairy goats, the disease can be exacerbated by the stress of lactation and the frequent handling of udders during milking, which can spread lesions. Additionally, the zoonotic potential of the virus means that human handlers can become infected, potentially serving as a source of infection for other animals.

The clinical signs of contagious ecthyma vary depending on the age of the animal and the site of infection. In lambs and kids, the most common presentation is the development of papules, vesicles, and pustules on the lips, muzzle, and oral mucosa, which progress to thick, brown, scabby lesions. These lesions can be painful, leading to reluctance to eat and subsequent weight loss. In severe cases, lesions may extend into the oral cavity, causing stomatitis and difficulty in nursing. The lesions typically resolve within 3 to 4 weeks, leaving no permanent scarring. In adult ewes and does, lesions may appear on the udder and teats, causing pain and leading to mastitis. Affected animals may be reluctant to allow nursing, resulting in poor lamb/kid growth. Lesions on the feet can cause lameness, and in some cases, lesions may appear on the perineum, vulva, or prepuce. Systemic signs are usually absent, but secondary bacterial infections can lead to fever, depression, and in severe cases, death. In goats, lesions may be more severe and prolonged, and can affect the oral cavity more extensively. The disease can also cause lesions on the coronary band, leading to foot rot-like symptoms. In some outbreaks, a severe proliferative form of the disease, known as 'orf of the head', can occur, with extensive cauliflower-like lesions on the face and ears. The lesions are highly contagious, and the scabs contain infectious virus, so handling affected animals requires precautions to prevent zoonotic transmission.

Differential diagnoses for contagious ecthyma include other causes of vesicular, pustular, and proliferative skin lesions in sheep and goats. These include: 1) Bluetongue (BT): A viral disease transmitted by Culicoides midges, causing fever, oral lesions, and coronitis. BT lesions are more ulcerative and hemorrhagic, and affected animals often show lameness and respiratory signs. PCR and serology can differentiate. 2) Foot-and-mouth disease (FMD): A highly contagious vesicular disease affecting cloven-hoofed animals, causing vesicles on the mouth, feet, and teats. FMD is a reportable disease, and laboratory confirmation is essential. 3) Sheep pox and goat pox: Caused by capripoxviruses, these diseases cause generalized skin nodules and systemic signs, including fever and respiratory distress. The lesions are more widespread and deeper than orf. 4) Ulcerative dermatosis (UVD): A viral disease caused by a parapoxvirus, causing lesions on the lips, nose, and genitalia, but with more ulceration and less proliferation than orf. 5) Photosensitization: Caused by ingestion of photodynamic agents, leading to erythema and scabbing on non-pigmented skin, but lesions are not typically vesicular or proliferative. 6) Bacterial dermatitis: Such as staphylococcal dermatitis, which can cause pustules and scabs, but is usually secondary to other conditions. 7) Mycotic dermatitis (dermatophilosis): Caused by Dermatophilus congolensis, leading to scabby lesions, but these are typically more crusty and less proliferative. 8) Nutritional deficiencies: Such as zinc deficiency, which can cause parakeratosis and skin lesions, but these are usually more generalized. Diagnosis is based on clinical signs, history, and laboratory tests, including PCR, electron microscopy, and virus isolation.

The diagnostic approach for contagious ecthyma begins with a thorough flock history and clinical examination. The presence of characteristic proliferative, scabby lesions on the lips, muzzle, and udder in lambs and ewes is highly suggestive. A presumptive diagnosis can be made based on clinical signs, especially during an outbreak. To confirm the diagnosis, laboratory testing is recommended. The diagnostic algorithm is as follows: 1) Collect scab or lesion samples from affected animals, preferably from early lesions (papules or vesicles) before secondary bacterial contamination. 2) Submit samples for PCR testing, which is the most sensitive and specific method for detecting ORFV DNA. 3) Alternatively, electron microscopy can be used to visualize parapoxvirus particles, which have a characteristic ovoid shape and criss-cross surface pattern. 4) Virus isolation can be performed on cell cultures, but it is less commonly used due to the difficulty of growing ORFV. 5) Serology, such as ELISA, can detect antibodies, but is less useful for acute diagnosis. 6) Rule out other differential diagnoses, such as bluetongue, FMD, and sheep pox, especially if the lesions are atypical or if there is high mortality. 7) In cases of secondary bacterial infection, bacterial culture and sensitivity testing may be indicated to guide antimicrobial therapy. 8) Implement biosecurity measures to prevent spread, and consider vaccination in endemic flocks. The diagnostic algorithm should be integrated with flock management practices to minimize economic losses.

Laboratory findings in contagious ecthyma are primarily related to the detection of the virus or the host's immune response. PCR is the preferred method for detecting ORFV DNA in scab material, skin biopsies, or vesicular fluid. The test is highly sensitive and specific, and can differentiate ORFV from other parapoxviruses. Electron microscopy can also be used to visualize the virus, which has a characteristic morphology. Virus isolation in cell cultures, such as ovine fetal lamb kidney cells, is possible but is less commonly performed due to the difficulty of growing the virus. Serological tests, such as ELISA, can detect antibodies against ORFV, but are not useful for acute diagnosis as antibodies may not be present until 7-10 days after infection. Hematological and biochemical parameters are usually within normal limits, unless there is a secondary bacterial infection, which may cause leukocytosis and elevated acute phase proteins. In cases of mastitis, milk samples may show an elevated somatic cell count and the presence of bacteria. Histopathology of skin lesions shows characteristic changes, including epidermal hyperplasia, ballooning degeneration of keratinocytes, and intracytoplasmic eosinophilic inclusion bodies. The diagnosis is often made based on clinical signs and confirmed by PCR. In outbreak situations, it is important to rule out other viral diseases, such as bluetongue and FMD, which require specific laboratory testing.

Imaging is not typically used in the diagnosis of contagious ecthyma, as the lesions are visible on the skin and mucous membranes. However, in cases where lesions are suspected to involve deeper structures, such as the oral cavity or the udder, imaging may be helpful. Ultrasonography can be used to evaluate the udder for mastitis, which may be a complication of orf lesions on the teats. Ultrasound can detect changes in the mammary gland parenchyma, such as increased echogenicity, abscessation, or fibrosis. In cases of foot lesions, radiography may be used to rule out underlying bone involvement, such as osteomyelitis. However, these imaging modalities are not routinely performed in the diagnosis of orf. The diagnosis is primarily based on clinical examination and laboratory testing. In research settings, advanced imaging techniques, such as computed tomography, may be used to study the extent of lesions, but this is not practical in clinical practice. Therefore, imaging plays a limited role in the diagnosis and management of contagious ecthyma.

Cytological and histopathological examination of orf lesions can aid in diagnosis. Cytology of impression smears from early lesions may show epithelial cells with ballooning degeneration and intracytoplasmic inclusion bodies, which are eosinophilic and may be seen in the cytoplasm of keratinocytes. However, cytology is less sensitive than PCR and is not commonly used. Histopathology of skin biopsies is more definitive. The characteristic findings include: 1) Epidermal hyperplasia with acanthosis and papillomatosis, 2) Ballooning degeneration of keratinocytes, 3) Intracytoplasmic eosinophilic inclusion bodies (Bollinger bodies), which are pathognomonic for parapoxvirus infections, 4) Dermal edema and infiltration with mononuclear cells, 5) Proliferation of capillaries and endothelial cells, consistent with the viral VEGF effect. In cases of secondary bacterial infection, there may be neutrophilic infiltration and abscess formation. Histopathology can also help differentiate orf from other diseases, such as sheep pox, which causes more extensive necrosis and intracytoplasmic inclusion bodies in various cell types. In cases of mastitis, histopathology of the mammary gland may show interstitial mastitis with lymphocytic infiltration and epithelial changes. Overall, histopathology is a valuable diagnostic tool, especially when PCR is not available.

Treatment of contagious ecthyma is primarily supportive, as the disease is self-limiting. The main goals are to prevent secondary bacterial infections, manage pain, and ensure adequate nutrition and hydration. In mild cases, no treatment is necessary, and lesions resolve within 3-4 weeks. However, in severe cases, particularly in young animals with extensive oral lesions, supportive care is essential. This may include: 1) Providing soft, palatable feed and ensuring access to water. 2) In cases of severe oral lesions, tube feeding may be necessary to maintain nutrition. 3) Topical application of antiseptic or antibiotic ointments to lesions to prevent secondary infection. 4) Systemic antibiotics, such as oxytetracycline (10 mg/kg IM q24h) or penicillin (20,000 IU/kg IM q24h), may be indicated if secondary bacterial infection is present. 5) Non-steroidal anti-inflammatory drugs (NSAIDs), such as flunixin meglumine (1.1-2.2 mg/kg IV or IM q24h) or meloxicam (0.5 mg/kg PO q24h), can be used to reduce pain and inflammation. 6) In cases of mastitis, intramammary antibiotics may be administered, and the affected gland should be milked out frequently. 7) In severe outbreaks, vaccination of unaffected animals may be considered, using a live attenuated vaccine. However, vaccination is not recommended during an outbreak as it can exacerbate lesions. 8) Biosecurity measures, such as isolating affected animals and disinfecting equipment, are crucial to prevent spread. The zoonotic risk should be communicated to handlers, and personal protective equipment should be used. The prognosis is generally good, but severe cases can lead to death, especially in young animals with secondary infections.

The prognosis for contagious ecthyma is generally good, with most animals recovering within 3-4 weeks. Mortality is low, typically less than 1%, but can be higher in young animals with severe oral lesions that prevent feeding, or in cases of secondary bacterial infections, such as mastitis or pneumonia. The prognosis is worse in animals with concurrent diseases, poor nutrition, or immunosuppression. In dairy goats, mastitis can lead to reduced milk production and increased culling. The disease can also have long-term economic impacts due to reduced weight gain and increased labor for treatment. In flocks with recurrent outbreaks, vaccination may be recommended to reduce the severity and frequency of outbreaks. The zoonotic potential of the virus means that human infections can occur, but these are usually self-limiting and resolve within a few weeks. However, in immunocompromised individuals, lesions can be more severe and may require medical treatment. Overall, the prognosis is favorable, but the disease can cause significant economic losses, particularly in intensive production systems.

Follow-up care for contagious ecthyma involves monitoring affected animals for resolution of lesions and the development of complications. Animals should be examined regularly to ensure that lesions are healing and that there are no signs of secondary infection, such as purulent discharge, swelling, or fever. In cases of mastitis, milk production and udder health should be monitored, and milk should be cultured if mastitis is suspected. Affected animals should be isolated from the rest of the flock until lesions have completely healed to prevent spread. The environment should be cleaned and disinfected, although the virus is resistant to many disinfectants. A 10% bleach solution or a commercial disinfectant effective against poxviruses should be used. Scabs and contaminated bedding should be removed and disposed of properly. In endemic flocks, a vaccination program should be implemented, with lambs and kids vaccinated at 2-3 months of age, and annual boosters for adults. The vaccine is a live attenuated virus and should be administered by scarification. It is important to note that the vaccine can cause lesions in humans, so precautions should be taken during administration. Flock biosecurity should be reviewed to prevent the introduction of the virus, including quarantine of new animals and disinfection of equipment. The zoonotic risk should be communicated to all personnel, and appropriate personal protective equipment should be used when handling affected animals.

Clinical pearls: 1) Contagious ecthyma is a common cause of scabby lesions on the lips and muzzle of lambs and kids, and the diagnosis is often straightforward based on clinical signs. 2) The disease is zoonotic, so always wear gloves when handling affected animals and lesions. 3) Lesions on the udder of ewes and does can lead to mastitis and poor lamb/kid growth, so monitor for this complication. 4) The virus is highly resistant in the environment, so thorough cleaning and disinfection are essential to prevent recurrence. 5) Vaccination is effective in reducing the severity of outbreaks, but should be used in endemic flocks, not during an outbreak. 6) Secondary bacterial infections are common, so consider prophylactic antibiotics in severe cases. 7) The disease is self-limiting, but supportive care is important to ensure adequate nutrition and hydration. Pitfalls: 1) Failing to consider other viral diseases, such as bluetongue or FMD, which can have similar lesions but require different management and reporting. 2) Using the vaccine during an outbreak, which can exacerbate lesions. 3) Neglecting biosecurity measures, leading to spread within the flock and to other flocks. 4) Underestimating the zoonotic risk, leading to human infections. 5) Not monitoring for mastitis in lactating animals, which can have long-term economic impacts. 6) Using ineffective disinfectants, as the virus is resistant to many common disinfectants. 7) Failing to provide supportive care in severe cases, leading to increased mortality.

There is no specific antiviral treatment for contagious ecthyma. Treatment is supportive and aimed at preventing secondary infections. The following drug protocols are commonly used in small ruminants, based on Plumb's Veterinary Drug Handbook and AASRP guidelines: 1) Antibiotics: Oxytetracycline (10 mg/kg IM q24h) or procaine penicillin G (20,000 IU/kg IM q24h) for 3-5 days, if secondary bacterial infection is present. 2) NSAIDs: Flunixin meglumine (1.1-2.2 mg/kg IV or IM q24h) or meloxicam (0.5 mg/kg PO q24h) for 1-3 days, to reduce pain and inflammation. 3) Topical antiseptics: Povidone-iodine solution or chlorhexidine solution applied to lesions daily. 4) In cases of mastitis, intramammary antibiotics, such as cephapirin or amoxicillin, may be administered, but should be based on culture and sensitivity. 5) Fluid therapy: In animals with severe oral lesions that are unable to eat or drink, intravenous fluids (e.g., lactated Ringer's solution) may be necessary. 6) Nutritional support: In severe cases, tube feeding with a milk replacer or gruel may be required. 7) Vaccination: A live attenuated orf vaccine is available and should be administered by scarification on the inner thigh or ear. The vaccine is not recommended during an outbreak. Withdrawal times for meat and milk should be observed for all medications, and local regulations should be followed.

Contagious ecthyma is a well-studied disease in small ruminants, with a substantial body of literature. Key studies have characterized the molecular biology of ORFV, including the role of viral immunomodulatory proteins in pathogenesis. Field trials have demonstrated the efficacy of live attenuated vaccines in reducing the severity and duration of outbreaks. A study by Nandi et al. (2011) reviewed the epidemiology and control of orf, highlighting the importance of biosecurity and vaccination. Another study by Hosamani et al. (2009) evaluated the use of a homologous inactivated vaccine, showing promising results. Research on the zoonotic potential of ORFV has emphasized the need for personal protective equipment when handling affected animals. The economic impact of orf has been assessed in several studies, with losses attributed to reduced weight gain, mastitis, and treatment costs. Consensus guidelines from the American Association of Small Ruminant Practitioners (AASRP) and the European College of Small Ruminant Health Management (ECSRHM) recommend vaccination in endemic flocks and strict biosecurity measures to prevent introduction. Overall, the evidence supports the use of vaccination as a key control measure, along with good management practices to reduce the impact of the disease.