Lumpy skin disease has been widespread among cattle this summer and is also occurring in young calves.
By Carien Kruger, senior journalist at African Farming and Landbouweekblad
What is unusual about lumpy skin disease this summer is that young calves are contracting the disease, and some have died, says veterinarian Dr Dave Midgley, CEO of the Ruminant Veterinary Association of South Africa (RuVASA).
Arend van den Berg, a plumber from Bloemfontein who until recently kept a small herd of Brangus cattle between Kroonstad and Edenville for extra income, says he lost four of his 20 open heifers to lumpy skin disease. “The whole herd, including my one bull, was covered in the lumps,” he says.
Van den Berg did not vaccinate his cattle because lumpy skin disease occurs in his herd every year and the animals usually recover. “This was the first time it was this bad,” he says.
The heifers’ joints became very painful, they struggled to walk, and some simply lay down and did not move. As a result, they did not eat or drink water. Van den Berg treated his herd with antibiotics, but it could not save the four heifers – they died from the infection caused by the disease.
As a result, Van den Berg lost his entire profit for the year. “I don’t want to take that risk again and I’m busy selling the cattle.”
Also read: Lumpy skin disease – what you need to know
Why the Disease Is More Prevalent This Year
Midgley says calves from vaccinated mothers are usually vaccinated against the disease after the age of six months because they have good immunity until then, thanks to the antibodies in the colostrum they receive within the first few hours after birth. He is aware, however, of cases this summer where such calves still became ill.
He attributes the higher occurrence of the disease this year to the wet summer following several years of drought, which has led to more mosquitoes. The disease is mainly transmitted by biting insects such as mosquitoes, biting flies and ticks.
Vaccination Timing Is Critical
Midgley says it is important that farmers vaccinate animals in time, namely in spring and early summer, which allows the animals enough time to build immunity against the virus.
Over the past few years there has been clear evidence that lumpy skin disease in the summer rainfall regions occurs mainly from October to April, with a peak around February and March, says Dr Otto Koekemoer, head of research and development at Design Biologix, one of the manufacturers of a vaccine against the disease.
He adds that the disease occurs in all nine provinces, and that farmers in the Western Cape can vaccinate a few months earlier.
Regarding possible cases of lumpy skin disease in young calves from vaccinated mothers, Koekemoer says it is important to remember that maternal immunity can only be effectively transferred to the calf if the cow was vaccinated during the last three to four months of pregnancy and the calf received colostrum on the first day after birth. “In any other case, calves can be vaccinated from two to three months of age, with a booster at one year.”
How and Why the Disease Spreads
Koekemoer says it is suspected that the disease may also be transmitted in the absence of insects, leading to the theory that the virus could spread through shared objects such as fence posts, feed troughs and especially water troughs.
Dr Danie Odendaal, managing director of the Veterinary Network (V-Net), says this type of transmission has not been proven in South Africa. “Transmission has only been proven through biting insects and ticks.”
Koekemoer adds that the second – and probably the most important – factor determining why more animals contract lumpy skin disease in one season than in previous seasons is the level of immunity within herds. “There is a general pattern that farmers vaccinate less during periods when the disease is not very prevalent. In the following season there are then many more unprotected animals that develop lumpy skin disease, and the common conclusion is that the disease has suddenly become more widespread.”
Also read: Lumpy skin disease in cattle
Immune Response Differs
Koekemoer says the vaccine itself remains unchanged. “There are strict regulations that require vaccine manufacturers to ensure that the original seed material used in vaccine production does not vary.”
However, he says there is significant variation in immune response between breeds and even between individual animals within the same herd. Factors that influence an animal’s overall health – such as nutrition, parasite load, stress and other infectious diseases – play a major role in an animal’s ability to develop effective immunity.
Koekemoer adds that factors on the vaccine side, such as the manufacturing process and the storage and transport of vaccines under cold-chain conditions, can also affect effectiveness. “Factors that result in insufficient live virus particles being available at the time of vaccination will make the vaccination less effective.”
When to Vaccinate for Optimal Protection
Koekemoer says vaccination should be done early enough to ensure optimal immunity in the herd by the time the risk of disease transmission is highest. “At this stage, the best way to predict this is to look at previous peak periods of outbreaks and insect activity in a specific region.”
Although it has not yet been scientifically proven, there are strong indications that insects – particularly larger biting insects and ticks – transmit the disease mechanically. “This means they do not multiply the virus but merely carry infected blood from one animal to another.”
He advises farmers to consult a veterinarian familiar with outbreak patterns about the optimal time for vaccination.
Also read: Ask the experts: This is how a vaccine booster dose works
Can the Lumpy Skin Virus Mutate?
“Any virus can mutate,” Koekemoer says. “The virus that causes lumpy skin disease, as well as the live virus used in vaccines, is a poxvirus with a double-stranded DNA genome. This group of viruses is known to be genetically very stable compared with viruses that have an RNA genome, such as the bluetongue virus.”
He says the genetic composition of the virus is monitored over time and very little variation has been observed. “This means the immunity generated by the vaccine virus will still neutralise all circulating viruses.”
Investigating suspected vaccine failures also forms part of Design Biologix’s quality-control programme. “We would appreciate it if animal owners and veterinarians contact us with the history and circumstances surrounding such cases. If the animals were vaccinated, we also request the vaccine batch number.”
Treatment and Support for Infected Cattle
Midgley says farmers who did not vaccinate their cattle preventatively in spring or early summer can now implement insect control, including the use of dipping chemicals. This helps prevent insects from biting or landing on the animals and spreading the disease further.
If animals are grazing in marshy areas, farmers should move them to higher ground.
Animals that contract the disease can be treated with antibiotics to control secondary bacterial infections, as well as anti-inflammatory and pain-relief injections.
Midgley advises farmers to discuss possible treatments with their local or herd veterinarian, and to observe meat and milk withdrawal periods.
Although a drier period is expected later this year, it remains best for farmers to vaccinate preventatively in spring or early summer, he says.
Odendaal agrees. “The vaccine is highly effective, and in herds where vaccination has been carried out annually according to a plan drawn up by the herd veterinarian, the disease has not occurred.”
Also read: Vet says he has a remedy for fatal bovine disease (snotsiekte)
