Lumpy Skin Disease

Lumpy skin disease (LSD) is a highly contagious, economically devastating viral disease of cattle caused by the Lumpy skin disease virus (LSDV), a member of the genus Capripoxvirus within the family Poxviridae. The disease is characterized by fever, generalized nodular skin lesions, lymphadenopathy, edema, and sometimes death. LSD affects both dairy and beef cattle, with significant morbidity and mortality, leading to severe economic losses due to decreased milk production, weight loss, hide damage, infertility, and trade restrictions. The disease is endemic in Africa and the Middle East, with recent outbreaks in Europe and Asia, posing a global threat. In cattle, LSDV infection can result in a wide spectrum of clinical manifestations, from subclinical to severe systemic disease, with mortality rates typically low (1-5%) but morbidity can reach up to 100% in naive herds. The disease is of major importance in intensive dairy systems, where high-yielding cows are more susceptible to severe clinical signs and production losses. Control measures include vaccination, biosecurity, and movement restrictions, as LSD is a notifiable disease to the World Organisation for Animal Health (WOAH).

The causative agent is Lumpy skin disease virus (LSDV), a double-stranded DNA virus belonging to the genus Capripoxvirus, family Poxviridae. LSDV is closely related to sheeppox virus and goatpox virus, but is host-specific to cattle. The virus is relatively stable in the environment, surviving in dried scabs for up to 35 days, and can persist in contaminated premises for months. It is inactivated by lipid solvents, detergents, and common disinfectants such as sodium hypochlorite, formalin, and phenol. The virus replicates in the skin, mucosa, and internal organs, causing characteristic nodular lesions. There are several strains of LSDV, with varying virulence. The virus is transmitted mechanically by blood-feeding arthropod vectors, primarily mosquitoes (e.g., Aedes aegypti) and stable flies (Stomoxys calcitrans), but also ticks. Iatrogenic transmission via contaminated needles and fomites is also possible. The virus enters through the skin, replicates locally, and then spreads via the lymphatic system and bloodstream to cause systemic infection.

LSD is endemic in sub-Saharan Africa, Egypt, and the Middle East, with recent epizootics in Turkey, the Balkans, Russia, and Asia. The disease affects cattle of all ages and breeds, but dairy breeds (e.g., Holstein-Friesian) are more susceptible to severe clinical disease than indigenous breeds. Morbidity rates range from 5% to 100%, with mortality typically 1-5%, but can be higher in calves and severely affected animals. The disease is more prevalent in warm, humid seasons when vector populations are high. Transmission is primarily mechanical via arthropod vectors, with a short incubation period of 4-14 days. The disease spreads rapidly in naive herds, with high morbidity. Economic losses arise from decreased milk production (up to 50% in dairy cows), weight loss, abortion, infertility, hide damage, and trade restrictions. In endemic areas, vaccination is practiced to control the disease. The disease is a significant constraint to cattle production and international trade.

After inoculation via a vector bite, LSDV replicates in the skin at the site of entry, causing local inflammation. The virus then spreads to regional lymph nodes, where it undergoes further replication, leading to viremia. The viremia results in systemic dissemination to the skin, mucous membranes, and internal organs. In the skin, the virus infects endothelial cells and fibroblasts, causing vasculitis, thrombosis, and necrosis, leading to the formation of characteristic nodules. These nodules are firm, raised, and may become necrotic or ulcerate. Systemic effects include fever, depression, anorexia, and reduced milk production. The virus can also cause lesions in the respiratory and gastrointestinal tracts, leading to pneumonia and diarrhea. In pregnant cows, abortion may occur due to placental infection. The immune response involves both humoral and cell-mediated immunity, but the disease can be severe in immunocompromised animals. The pathogenesis is similar to other poxvirus infections, with a strong inflammatory response and tissue necrosis.

Intrinsic factors: High milk production, young age (calves and young stock are more susceptible), stress (e.g., transport, parturition), immunosuppression (e.g., concurrent diseases, poor nutrition), and genetic susceptibility (dairy breeds more susceptible). Extrinsic factors: High vector density (warm, humid climates), poor biosecurity, introduction of infected animals, contaminated equipment (needles, tattooing instruments), and lack of vaccination. Management practices such as overcrowding and poor sanitation can increase the risk of transmission. In endemic areas, cattle that have recovered from LSD develop lifelong immunity, but naive herds are at high risk of severe outbreaks.

The incubation period is 4-14 days. Clinical signs include fever (40-41.5°C), which may persist for 1-2 weeks, followed by the appearance of multiple firm, circumscribed nodules (1-5 cm in diameter) on the skin, particularly on the head, neck, perineum, udder, and limbs. The nodules may become necrotic and slough, leaving deep ulcers that heal slowly. There is marked lymphadenopathy, especially of the superficial lymph nodes. Affected cattle show depression, anorexia, reduced milk yield, and weight loss. Mucous membranes may have lesions, leading to nasal discharge, salivation, and conjunctivitis. Edema of the limbs and brisket may occur. In severe cases, pneumonia, diarrhea, and abortion can occur. The disease can be complicated by secondary bacterial infections, leading to mastitis and lameness. The clinical course lasts 2-4 weeks, but lesions may take months to heal. In some cases, the disease is subclinical, with only mild fever and few nodules.

Differential diagnoses include: 1) Bovine papular stomatitis (caused by parapoxvirus, lesions on muzzle and oral mucosa, less severe). 2) Pseudocowpox (parapoxvirus, lesions on teats and udder, milder). 3) Dermatophilosis (bacterial skin infection, crusty lesions, not nodular). 4) Insect bites and urticaria (allergic reactions, transient, no fever). 5) Bovine herpes mammillitis (ulcerative lesions on teats, no systemic signs). 6) Foot-and-mouth disease (vesicular lesions on feet and mouth, highly contagious). 7) Bovine viral diarrhea (mucosal lesions, diarrhea, immunosuppression). 8) Malignant catarrhal fever (high fever, erosive lesions, neurological signs). 9) Photosensitization (skin lesions on unpigmented areas, no fever). 10) Besnoitiosis (protozoal infection, skin thickening and cysts). Definitive diagnosis is based on PCR, virus isolation, or serology.

1) Herd history: Recent introduction of cattle, presence of vectors, vaccination status, and clinical signs. 2) Physical examination: Identify characteristic nodules, fever, lymphadenopathy, and systemic signs. 3) Differential diagnosis: Rule out other skin diseases. 4) Laboratory confirmation: Collect skin nodule biopsies, scabs, or vesicular fluid for PCR (preferred), virus isolation, or electron microscopy. 5) Serology: Virus neutralization test or ELISA to detect antibodies (useful for retrospective diagnosis). 6) Histopathology: Skin biopsy showing characteristic intracytoplasmic inclusion bodies (eosinophilic) in epithelial cells. 7) Report to veterinary authorities as a notifiable disease. 8) Implement control measures: quarantine, movement restrictions, vaccination of in-contact animals, and vector control.

Hematology: Leukopenia (due to lymphopenia) in the early stages, followed by leukocytosis with neutrophilia in secondary bacterial infections. Serum biochemistry: Elevated acute-phase proteins (haptoglobin, serum amyloid A), increased fibrinogen, and mild hypoalbuminemia. Virology: PCR on skin lesions or blood is highly sensitive and specific. Virus isolation in cell culture (e.g., bovine kidney cells) is confirmatory but slower. Serology: Virus neutralization test or ELISA can detect antibodies, but seroconversion occurs 1-2 weeks after infection. Histopathology: Skin biopsy shows epidermal necrosis, ballooning degeneration of keratinocytes, and intracytoplasmic inclusion bodies (Bollinger bodies). No specific changes in rumen fluid or blood gas are expected unless secondary complications occur.

Imaging is not routinely used for LSD diagnosis. However, ultrasonography of skin nodules may show hypoechoic areas due to necrosis and edema. Thoracic ultrasound may reveal lung consolidation in cases of pneumonia. Radiography is not helpful. In cases of abortion, fetal necropsy may show characteristic lesions. Advanced imaging is not necessary for diagnosis, which relies on clinical signs and laboratory confirmation.

Cytology: Fine-needle aspirates of nodules may show necrotic debris, inflammatory cells, and occasional epithelial cells with intracytoplasmic inclusion bodies. Histopathology: Skin biopsy reveals severe epidermal necrosis, ballooning degeneration of keratinocytes, and characteristic eosinophilic intracytoplasmic inclusion bodies (Bollinger bodies) in epithelial cells. There is also dermal edema, vasculitis, thrombosis, and infiltration of macrophages and lymphocytes. In severe cases, there is full-thickness skin necrosis and ulceration. Similar lesions may be seen in the mucosa of the respiratory and gastrointestinal tracts. The presence of inclusion bodies is pathognomonic.

There is no specific antiviral treatment for LSD. Treatment is supportive and aimed at controlling secondary bacterial infections and alleviating clinical signs. 1) Supportive care: Provide clean, dry, and comfortable housing; ensure adequate nutrition and hydration. 2) Anti-inflammatory drugs: Flunixin meglumine (2.2 mg/kg IV or IM, q24h) or meloxicam (0.5 mg/kg IV or SC, q48h) to reduce fever and inflammation. 3) Antibiotics: To prevent or treat secondary bacterial infections, use broad-spectrum antibiotics such as oxytetracycline (10 mg/kg IM or SC, q24h) or ceftiofur (2.2 mg/kg SC, q24h) for 3-5 days. 4) Wound care: Clean and disinfect skin lesions with antiseptic solutions (e.g., chlorhexidine). 5) Fluid therapy: If dehydrated, administer oral or IV fluids. 6) Vaccination: In an outbreak, vaccinate all healthy in-contact cattle with a live attenuated LSD vaccine (e.g., Neethling strain) to reduce spread. 7) Vector control: Use insecticides and repellents to reduce vector populations. 8) Biosecurity: Quarantine affected animals, restrict movement, and disinfect equipment.

The prognosis is generally good in uncomplicated cases, with recovery in 2-4 weeks. However, severe cases with extensive skin necrosis, secondary infections, or systemic complications may have a guarded prognosis. Mortality is low (1-5%), but morbidity can be high, leading to significant production losses. Milk production may not return to pre-infection levels for several weeks or months. Culling may be necessary for animals with severe hide damage or chronic mastitis. The disease can have long-term effects on fertility and growth. In naive herds, the economic impact can be devastating.

After an outbreak, monitor cattle for at least 30 days for new lesions. Implement a vaccination program for all cattle in the herd and surrounding areas. Maintain strict biosecurity measures, including vector control and disinfection of equipment. Regularly inspect animals for signs of disease. In dairy herds, monitor milk production and udder health, as mastitis may occur. For animals that recovered, ensure complete healing of skin lesions to prevent secondary infections. Work with veterinary authorities to comply with regulations and trade restrictions. Conduct serological monitoring to assess herd immunity.

Pearls: 1) LSD should be suspected in any cattle with fever and multiple skin nodules, especially in endemic areas or after vector exposure. 2) The disease is notifiable; report suspected cases immediately. 3) Vaccination is the most effective control measure; use a live attenuated vaccine in healthy animals during an outbreak. 4) Vector control is crucial to reduce transmission. 5) Supportive care with NSAIDs and antibiotics can improve recovery. Pitfalls: 1) Misdiagnosis as insect bites or other skin diseases can delay control. 2) Failure to implement quarantine and movement restrictions can lead to rapid spread. 3) Using contaminated needles or equipment can iatrogenically spread the virus. 4) Vaccinating animals already incubating the disease may not prevent clinical signs. 5) Neglecting secondary bacterial infections can lead to severe complications.

There is no specific antiviral drug for LSD. Supportive therapy includes: 1) Flunixin meglumine: 2.2 mg/kg IV or IM, q24h, for 1-3 days. Withdrawal: milk 36 hours, meat 4 days. 2) Meloxicam: 0.5 mg/kg IV or SC, single dose, may repeat after 48 hours. Withdrawal: milk 72 hours, meat 15 days. 3) Oxytetracycline: 10 mg/kg IM or SC, q24h, for 3-5 days. Withdrawal: milk 72 hours, meat 28 days. 4) Ceftiofur: 2.2 mg/kg SC, q24h, for 3-5 days. Withdrawal: milk 0 hours, meat 3 days. 5) Procaine penicillin G: 22,000 IU/kg IM, q24h, for 3-5 days. Withdrawal: milk 48 hours, meat 10 days. 6) For wound care, use chlorhexidine solution (0.5%) topically. 7) Vaccination: Live attenuated LSD vaccine (Neethling strain) administered SC, 1 mL per animal, as per manufacturer's instructions. Withdrawal: none. Always follow label directions and consult a veterinarian.

LSD has been extensively studied in Africa and the Middle East. Key findings include: 1) The disease is transmitted primarily by mechanical vectors, with Stomoxys calcitrans and Aedes aegypti being important. 2) Live attenuated vaccines (Neethling strain) provide effective protection, with a single dose conferring immunity for at least 3 years. 3) In outbreaks, vaccination of in-contact animals can reduce spread. 4) Morbidity and mortality vary, with dairy breeds more severely affected. 5) Economic losses are significant, with milk yield reductions of up to 50% and hide damage. 6) PCR is the most reliable diagnostic method. 7) Control measures include vaccination, vector control, and movement restrictions. Recent outbreaks in Europe and Asia highlight the need for global surveillance and preparedness. The WOAH has guidelines for LSD surveillance and control.