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Lumpy skin disease (LSD) is a growing concern among cattle farmers around the world. It is caused by a poxvirus (similar to the mpox virus in humans), called lumpy skin disease virus (LSDV). There is no evidence of LSDV infection in humans, but LSD primarily affects cattle and water buffalo, and has also been detected in wildlife such as springbok, impala, oryx and giraffes. LSD is a notifiable disease that must be reported, both locally to the National Department of Agriculture (NDA) and internationally to the World Organisation of Animal Health (WOAH), due to its potential as a transboundary disease.
What are the symptoms of LSD?
LSD causes a variety of distinct symptoms in cattle, the severity of which varies according to the virulence of the virus strain and the breed’s susceptibility. In natural outbreaks, the disease typically manifests after a three to twelve-day incubation period. The main symptoms to look out for are fever, which can exceed 41°C and last up to ten days in severe cases. The development of multiple skin nodules, which are firm and raised, ranging in size from 0,5 to 5cm, is a hallmark of LSD. These nodules appear throughout the body, but are most visible on the head, neck, udder, scrotum, vulva, and perineum. The superficial lymph nodes become swollen and palpable. Dairy cattle also produce significantly less milk.
Secondary symptoms include lameness from swollen limbs, painful nodules, and tendon inflammation. Increased ocular and nasal secretions are typical. Lack of appetite causes significant weight loss. Coughing and pneumonia are common respiratory problems caused by ulcerative lesions in the mouth and respiratory tract, while ulcerative lesions are also found in the digestive tract. Animals can also develop oedema and swelling of the limbs, brisket, and genitals. Bulls may experience reduced fertility or permanent infertility, whereas pregnant cows may have an abortion. In severe cases, corneal opacity and keratitis may occur. Secondary bacterial infections can also occur in open lesions.
What is the economic importance of LSD?
The disease has the potential to be devastating because it affects not only animal welfare, but also the farmer’s income. It can devastate farm finances in a variety of ways, including a drop in milk production, permanent damage to hides reducing their commercial value, temporary or permanent infertility in breeding stock, abortions in pregnant animals, weight loss and poor growth in beef cattle, treatment and control costs, and trade restrictions that limit market access.
What to do when cattle have LSD symptoms?
If a suspected case of LSD is discovered in a herd, the farmer must promptly notify the veterinarian or veterinary services (state) in the area, as LSD is a notifiable disease in South Africa. Separate and isolate sick or affected animals to prevent disease transmission. Animals, particularly sick animals, should not be immunised during an outbreak. There is no specific treatment for LSD, however, supportive care may include the use of antibiotics to prevent or treat secondary bacterial infections, anti-inflammatory medications to reduce fever and discomfort, and the provision of adequate nutrition and clean water to aid the animals’ recovery. It is critical to follow any control measures that the authorities implement.
LSD is transmitted primarily through arthropod vectors, which include blood-feeding insects like Culex mosquitoes, flies, and ticks. To further reduce transmission, insect-control measures must be implemented. These should include the use of insect repellents (e.g. deltamethrin), the installation of fly traps, and the removal of standing water to reduce mosquito breeding. Other routes of transmission, include direct contact with infected animals, which is less common, as well as contaminated feed, water sources, and needles.
How to prevent and control LSD?
The most effective way to control the disease, is to administer live-attenuated vaccines based on the Neethling strain of LSDV. Vaccination recommendations include immunising the entire herd prior to high-risk seasons (typically before summer and the rainy season), ensuring that calves from unvaccinated cows receive their first vaccine before six months of age, immunising calves from vaccinated cows at around six months of age, and administering annual booster vaccines.
Regular vaccinations, good biosecurity practices, early detection, and the implementation of serosurveillance studies to identify potential threats, remain the best defense against LSD. Preventive measures are much more cost-effective than managing and containing an LSD outbreak.
How can the ARC-OVR help?
Early detection is critical for controlling outbreaks. The most effective laboratory tests for diagnosing LSD, combine rapid molecular detection with virus characterisation to confirm outbreaks. Real-time and conventional polymerase chain reaction (PCR) are used to detect LSDV DNA in skin biopsies, EDTA blood, or scabs. Virus isolation can also be accomplished through skin biopsy samples and virus growth in cell culture. Serology tests are also available. These include the Virus Neutralisation Test (VNT) and an enzyme-linked immunosorbent assay (ELISA), which detect antibodies after infection or vaccination, and are useful for herd-level surveillance. The ARC-OVR will test suspect LSD samples submitted by a veterinarian and/or animal health technician without charge to the farmers from South Africa. – Pravesh Kara, Agricultural Research Council
For more information, contact Dr Antoinette van Schalkwyk of ARC-Onderstepoort Veterinary Institute on 012 529 9225 or email vanschalkwyka1@arc.agric.za or visit www.arc.agric.za
