Tuesday, November 29, 2022

The impact of lumpy skin disease

Estimated reading time: 4 minutes

Lumpy skin disease (LSD) in cattle continues to be of economic importance in South Africa and other sub-Saharan countries as it leads to various production losses, although its mortality rate is usually low. The disease has been confined to the African continent for most of the 20th century, but since 2011 it has spread from the Middle East to Europe, Russia and the majority of Asian countries.

The most distinctive clinical sign of this notifiable disease is widespread nodules (lumps) across the animal’s skin, accompanied by swelling of the lymph nodes. Infected cattle may initially develop lacrimation, fever, loss of appetite and a disinclination to move. According to the article Lumpy skin disease in Southern Africa: A review of the disease and aspects of control by Drs Pamela Hunter and David Wallace, skin nodules only appear approximately ten days after the initial temperature reaction.

The disease, they state, is widespread in South Africa in regions with climatic factors that favour the reproduction and spread of probable insect vectors. More research into vectors and the disease epidemiology is therefore essential to establish better local disease control.

Recent publications investigating the lumpy skin disease virus (LSDV) strains circulating in Asia suggest a new mode of transmission has arisen that is not dependent on insect vectors. It is important to note that the LSDVs circulating in Russia and Southeast Asia are genetically distinct from those observed in Africa.

Read more about vaccination plan guidelines for cattle herds here.

Economic implications

All cattle breeds can exhibit clinical signs ranging from mild to severe, or even remain asymptomatic. The disease is not only confined to cattle and has been reported in various antelope species, giraffe and water buffalo.

Dairy cattle are, however, generally more severely affected and can experience up to a 50% drop in milk production. Secondary mastitis can occur due to lesions on the teats and loss of some quarters of the udder, and cows may abort. General debilitation, loss of fertility in bulls and severe damage to hides also contribute to the negative impact of LSD.

Read more about the impact of drought on livestock here.

LSDV type Neethling

The excellent work performed at Onderstepoort from the 1950s onwards led to the isolation and characterisation of the true virus causing LSD, as opposed to other cattle viruses, some of which can induce similar clinical signs. The South African Neethling isolate was one of the first purified LSD viruses, and thus the virus became officially known as LSDV type Neethling. It belongs to the family Poxviridae.

Spread of the disease

Since LSD is probably most widely spread by biting flies, which are unlikely to serve as long-term maintenance hosts, it is unknown how it is maintained during inter-epidemic periods. The stable fly (Stomoxys calcitrans) is the most likely transmitter of LSD, whereas other biting insects such as horseflies, mosquitos and midges, or even ticks, may also be involved.

Extensive LSD outbreaks are mostly associated with periods of high rainfall and concomitant high levels of insect activity. It occurs during mild winters into summer, with a peak of activity during late summer/autumn.

Read more about game farming guidelines here.

Vaccination and immunity

Vaccination is the most effective option for controlling the spread of LSD. Antibodies are a useful measure of response to vaccination, but other parts of the immune system play an equally important role in conferring protection. Studies showed that the vaccine protected against all field strains tested. Occasional reports of vaccine failure are most likely due to infrequent or improper use of the vaccine.

Other aspects that were investigated in respect of vaccination include:

  • Vaccination of animals already incubating the disease is a relatively common occurrence, as many producers only consider vaccinating their animals in the face of an outbreak. Vaccination is then too late to protect these animals. Inadequate needle hygiene can also spread the disease during vaccination.
  • The shape of the lesions, disease severity, and the isolation of the virus from skin biopsy samples can assist in making a distinction between true LSD and pseudo-LSD (caused by the Allerton virus).
  • Vaccinated cows that develop an antibody response will confer maternal immunity to LSD by means of colostrum, which lasts for around six months. Calves may develop the disease at this age if not vaccinated timeously. Where some cows do not develop detectable antibody responses to vaccination, their calves may be susceptible to infection shortly after birth. – Christal-Lize Muller, Stockfarm

For more information, send an email to Dr Antoinette van Schalkwyk at vanschalkwyka1@arc.agric.za.