Lumpy skin disease (LSD) is a highly infectious disease of cattle and Asian water buffalo caused by the lumpy skin disease virus (LSDV). The virus is spreading at an alarming rate and the geographical distribution of LSD has reached unprecedented levels; the disease is now endemic across most of Africa and in recent years there have been outbreaks in many of the major cattle-producing regions of Asia, with fears that it will continue to spread further. Prompt action and effective disease control are vitally important in reducing the impact of this disease on farm incomes and improving animal welfare.
LSD is classified as a transboundary animal disease (TAD) meaning it is a highly contagious epidemic disease with the potential to spread rapidly across the globe with devastating effects on both local and international trade. The substantial economic impact of LSD led the World Organization for Animal Health (OIE) to categorise LSD as a notifiable disease (OIE, 2015). Whilst LSD generally has lower morbidity and mortality compared to some other OIE-listed livestock diseases, the prolonged loss of production in both dairy and beef cattle, together with the impact on international trade, means that LSD is one of the most important infectious cattle diseases facing the global livestock industry. Indeed, LSD has been reported to produce chronic debility in affected cattle comparable to that caused by foot and mouth disease.1
Direct economic losses result from decreased milk production, reduced weight gain, infertility, abortions, damaged hides and death of severely affected cattle. There are often substantial indirect losses too, caused by national and international cattle movement and trade restrictions.
Lumpy Skin Disease Symptoms: Knowing What to Look Out for The LSD virus belongs to the Capripoxvirus genus which also includes the sheeppox and goat pox viruses. The first phase of infection when the virus enters the bloodstream is known as the viraemic stage. At this time, infected cattle may have:
- Fever (40–41oC)
- Loss of appetite
- Discharge from eyes and nose
- Enlarged glands (lymph nodes)
- Increased salivation
Diagnosis is often based on the characteristic skin lesions that give the disease its name (Figure 1 and Figure 2). They start to develop in the following days and often in multiple animals at the same time:
- Circular, firm, elevated nodules (up to five centimetres in diameter, sometimes larger)
- Lesions may be localised to the head, neck and limbs or may cover the whole body
- Scabs form within one to two weeks which usually slough to leave an ulcer
- High risk of myiasis (fly strike) on open sores
Confirmatory samples including scabs, saliva, nasal secretions or blood may be taken for laboratory testing. The Polymerase chain reaction (PCR) test is one of the least expensive and quickest methods of detecting LSDV.
Transmission of the Virus: How Does it Spread?
The first (index) case in a herd is often associated with the movement of cattle. In the early stages of infection, clinical signs are usually mild and difficult to recognise even by experienced farmers or veterinarians. The incubation period of the virus can be as long as five weeks and by the time the characteristic skin lesions associated with more severe cases are detected, the virus has probably been circulating for some time and is likely to be well established within the herd. LSD is mainly transmitted by insect vectors. These vectors pick up the virus when they bite an infected animal and spread it to uninfected animals at their next blood meal. The most likely vectors are stable flies (Stomoxys calcitrans), mosquitoes (Aedes aegypti) and ticks (Rhipicephalus and Ambylomma species). Biting insects thrive in the warm, wet seasons and so there tend to be seasonal spikes in LSDV infection at these times, whilst disease incidence reduces in cooler winter months.
Once the infection is established, morbidity (the number of cases within a herd) ranges from 5% to 45%. Mortality rates tend to remain fairly low and are usually below 10%.2
The recent spread of LSD has been concerning and with global warming looking set to continue, insect vectors are likely to flourish, providing the perfect conditions for virus multiplication. Without adequate control measures, LSD is likely to become more of a threat to livestock in the coming years.