Lumpy skin disease (LSD) is a chronic acute poxviral disease of cattle that is spread by biting insects. The virus, which is closely related to the pox viruses of sheep and goats, and causes nodular skin lesions on the animal’s body. Although the mortality rate is generally low, losses occur from decreased milk production, abortion, infertility, loss of condition and damaged hides.
Lumpy skin disease is caused by a virus in the genus Capripoxvirus of the family Poxviridae. Lumpy skin disease virus (LSDV) is closely related antigenically to sheep and goat poxviruses. Although these three viruses are distinct, they cannot be differentiated with routine serological tests. Lumpy skin disease generally occurs in Africa; however outbreaks have occurred in parts of the Middle East.
The incubation period in the field is thought to be two to five weeks. In experimentally infected animals, fever can develop in 6 to 9 days and lesions first appear at the inoculation site in 4 to 20 days.
- Lumpy skin disease is primarily spread between animals by biting insects (vector), such as mosquitoes in the genera Aedes and Culex and biting flies.
- Less commonly, the virus may be spread by direct contact to the skin lesions, saliva, nasal discharge, milk, or semen of infected animals.
- Epidemics of LSD are associated with rainy seasons. The disease spreads in river basins and areas conducive to insect multiplication.
- LSDV occurs in cutaneous lesions, saliva, respiratory secretions, milk and semen. Shedding in semen may be prolonged; viral DNA has been found in the semen of some bulls for at least 5 months after infection.
- Animals can be infected experimentally by inoculation with material from cutaneous nodules or blood, or by ingestion of feed and water contaminated with saliva.
- LSDV is very resistant to inactivation, surviving in desiccated crusts for up to 35 days, and can remain viable for long periods in the environment.
- Disease can vary from mild to severe; younger animals are generally more severely affected. Animals will have a fever, be lethargic and unwilling to eat. The severity of the disease depends on the dose of the inoculum as well as the susceptibility of the host (Bos taura is more susceptible than Bos indicus) and the route of exposure.
- Animals may have discharge from the eyes and nose, drop in milk production and weight loss.
- The most apparent sign will be multiple nodules on the body which develop 2 days after appearance of the fever, including the muzzle, nostrils, head, neck, back, legs, scrotum, perineum, udder, eyelids, nasal and oral mucosa, and tail. These nodules may leak fluid and have an ulcerated center. Nodules can also develop in gastrointestinal tract, especially the abomasum (true stomach), as well as the trachea and lungs, resulting in primary and secondary pneumonia. The nodules are painful and involve the epidermis, dermis, and subcutaneous tissue and may even involve the musculature. As the disease progresses, the nodules become necrotic, and eventually a deep scab forms; this lesion is called a sitfast Secondary bacterial infection can complicate healing and recovery.
- Lameness may occur from inflammation of the tendons, and severe swelling of the brisket and legs. This lameness can be permanent with severe damage to tendons and joints from secondary bacterial infections (edema).
- Permanent damage may occur to teats and mammary glands due to secondary bacterial infections and mastitis.
- Abortion may occur as a result of prolonged fever and intrauterine infection are possible; temporary or permanent sterility in both bulls and cows may not come into estrus for several months after contracting the disease.
- Superficial lymph nodes such as the mandibular, parotid, prescapular, and prefemoral nodes, draining affected areas of skin become enlarged 4 to 10 times normal size.
- The lesions may persist in various stages over a course of 4 to 6 weeks. Final resolution of lesions may take 2 to 6 months, and nodules can remain visible 1 to 2 years. Permanent damage to the hide is inevitable in clinical cases.
- The clinical signs range from inapparent to severe. Host susceptibility, dose and route of virus inoculation affect the severity of disease. Young calves often have more severe disease than adults.
Treatment and control
- Treatment is directed at preventing or controlling secondary infection.
- Animals infected with LSDV generally recover (mortality is usually less than 3 percent). Complete recovery may take several months and may be prolonged where secondary bacterial infection occurs. Loss of production results from severe emaciation, lowered milk production, extensive damage to hides, and loss of draft from lameness. It may take up to 6 months for animals severely affected by LSDV to recover fully
- The most likely way for LSD to enter a new area is by introduction of infected animals. Biting insects that have fed on infected cattle may travel and be blown for substantial distances. The movement of contaminated hides represents another potential means for this resistant virus to move.
- If LSD is confirmed in a new area before extensive spread occurs, the area should be quarantined, infected and exposed animals slaughtered, and the premises cleaned and disinfected.
- Vaccination of susceptible animals within the quarantine should be considered.
- If the disease has spread over a large area, the most effective means of controlling losses from LSD is vaccination.
- However, even with vaccination, consideration still should be given to eliminating infected and exposed herds by slaughter, proper disposal of animals and contaminated material, and by cleaning and disinfecting contaminated premises, equipment, and facilities.
- Current insecticides together with repellents aid in the prevention of the spread of LSD.
- Import restrictions can help prevent the introduction of lumpy skin disease. This disease is mainly spread to new areas by infected animals Infected insects are suspected to have spread LSDV to new areas during some outbreaks.
- LSDV is susceptible to ether (20%), chloroform, formalin (1%), and some detergents, as well as phenol (2% for 15 minutes).
- This virus can survive for long periods in the environment: up to 35 days in desiccated scabs and for at least 18 days in air-dried hides.
- Monitor your animals frequently for any signs of disease, especially skin lesions or lameness.