Lumpy skin disease (LSD) is a viral disease that occurs across the globe. It is a transboundary disease that is categorised as a notifiable disease by the World Organization for Animal Health (OIE).
The disease is caused by lumpy skin disease virus (LSDV) that belongs to the family Poxviridae, genus Capripoxvirus. Sheep pox virus and Goat pox virus belong to the same genus. LSDV only occurs in cattle and domestic buffaloes and not in sheep, goats, wildlife, or humans.
The main means of transmission is believed to be by an arthropod vector, which may be mosquitoes (Culex mirificens and Aedes natrionus), biting flies (Stomoxys calcitrans and Biomyia fasciata) and male ticks (Riphicephalus appendiculatus and Amblyomma hebraeum).
Different vectors are likely to play a part in different areas, depending on how many there are and how they feed. Up to 20% of the animals may get the disease, and up to 5% may die as a result of it.
The virus does not multiply in the vector but is spread when they feed on different animals.
Direct contact and seminal, as well as intrauterine transmission, has been demonstrated in experiments. Early observations also showed that the virus can be transmitted via contaminated feed and water.
LSDV survives in the dead cells in the skin nodules for up to 33 days or longer, dry crusts for up to 35 days, and at least 18 days in air-dried hides. The virus is susceptible to sunlight and detergents that containing lipid solvents, but can stay viable for months in a dark, contaminated animal shed.
LSD is endemic in most African countries, especially in Southern Africa, also in many other African and Middle Eastern countries.
The disease was first noticed in Zambia in 1929, from where it had spread to Botswana and South Africa by 1943, leading to major economic losses. In 1957, it entered Kenya at the same time as an outbreak of sheep pox. In 1970, it spread north into the Sudan, and by 1974 it had spread west as far as Nigeria. In 1977, was reported from Mauritania, Mali, Ghana, and Liberia.
In 1981 and 1986 it spread to Tanzania, Kenya, Zimbabwe, Somalia, and Cameroon, with a reported mortality rate of 20% in affected cattle. Between 1988 and 1989, LSD was spread north of the Sahara Desert and outside the African continent in Egypt and Israel, where it was again reported in 2006.
In the past decade, it has also occurred in the Middle Eastern, European, and Asian regions. Between 2012 and 2022, the disease spread into south-east Europe, the Balkans, Russia, and Asia and forms part of the Eurasian LSD epidemic.
Lumpy skin disease outbreaks are reported almost every year in Zimbabwe, and it is spreading to areas previously free of the disease.
Outbreaks tend to occur during the warm and wet season and the months following the rainy season. This may be because there is increased arthropod activity during these climatic conditions. The frequency of reported outbreaks is highest in March and April, and the lowest reported cases occur in November.
Outbreaks are sporadic and depend upon animal movement, the presence of the vector population and the climatic conditions that affect them, and whether the animal had become immune due to prior exposure.
The severity of the symptoms varies and depends on the particular strain of the virus, as well as the breed and age of the animal. The European Bos taurus is generally more susceptible to the disease than the indigenous Bos indicus.
Even among groups of cattle of the same breed who are kept together under the same conditions, a large variation in the clinical symptoms occur, ranging from a mild infection to death.
After an experimental inoculation with the virus, it took six to nine days before the onset of fever. In an acutely infected animal, the temperature may exceed 41°C and can persist for a week. All the superficial lymph nodes become swollen. The limbs may also be swollen, and the animal does not want to move, eat, or drink.
Between seven to 19 days of virus inoculation, lesions or lumps develop all over the body, particularly on the head, neck, udder, scrotum, vulva, and perineum.
These nodules or lumps have a creamy grey to white colour when cut and may initially ooze amber-coloured fluid or serum. During the following two weeks a cone-shaped, central, necrotic core of dying cells may appear within the nodule.
Nodules may also develop in the mucous membranes of the mouth and entire digestive system, the respiratory tracts and on the surface of almost any internal organ.
The nodules on the mucous membranes of the eyes, nose, mouth, rectum, udder, and genitalia quickly form an ulcer. When it appears in the cornea of one or both eyes, it can lead to restricted vision or even blindness. At that stage, all secretions, eye and nasal discharge and saliva contain the LSD virus.
The disease is of economic importance as it can lead to less milk production, abortion, temporary or permanent sterility in bulls and infertility in both sexes, damage to hides, and even death, especially in animals that have not previously been exposed to the virus.
Also, the animals may not be moved or traded. The cost of vaccination and treatment, culling and loss of income due to a ban on movement and trade, add to the economic woes.
The thin, weak animal, which may have pneumonia and mastitis, recovers slowly.
Outbreaks that occur more frequently and in new areas, could indicate that control measures in Zimbabwe are not efficient. Control is done by means of vaccination, movement control and culling, but there are several challenges. Vaccination is good, but in Africa, prevention is better and cheaper than cure.
Farmers are the first line of defence against this highly contagious disease, but they may be reluctant to report an outbreak for fear of the consequences, like a ban on movement and trade. Delayed reporting of outbreaks will hamper successful control.
The failure of control could be as a result of viral factors such as genetic variations of the virus, failure of the vaccine because of improper shipping and handling, or unavailability and cost of vaccination and treatment, and the physical health of the animal, its breed and age, and its immune history.
During an outbreak, the movement of cattle must be controlled, but this is not always easy because small-scale farmers trade across borders despite it being illegal. Also, in some regions, farmers move animals between summer and winter pastures. To stop this, may lead to lack of food. The transport of animals prior to religious and cultural festivities, where animals are slaughtered, may also spread the disease.
Culling of infected or susceptible animals that have been exposed to infection, is recommended. However, in resource-limited countries this may not be affordable or feasible or may not even permitted by law or due to religious and traditional reasons.
Lumpy Skin Outbreak Hits Binga (2022) New Zimbabwe. https://www.newzimbabwe.com/lumpy-skin-outbreak-hits-binga/
Lumpy Skin Disease (2023) WOAH Terrestrial Manual Chapter 3.4.12. https://www.woah.org/fileadmin/Home/fr/Health_standards/tahm/3.04.12_LSD.pdf
Sigauke, S., Jeremiah, O.T., Oyedele, H., Dube, F. (2022) Lumpyskin disease vaccine: Awareness, availability, and accessibility to small-holder farmers in Midlands Zimbabwe. Acta Scientific Veterinary Sciences (ISSN: 2582-3183) Volume 4 Issue 6 June 2022 DOI: 10.31080/ASVS.2022.04.0404 https://actascientific.com/ASVS/pdf/ASVS-04-0404.pdf
Tuppurainnen,E., Dietze, K., Wolff, J., Bergmann, H., Beltran-Alcrudo, D., Fahrion, A., Lamien, C. E., Busch, F., Sauter-Louis, C., Conraths, F.J., De Clercq, K., Hoffmann, B., Knauf, S. (2021) Review: Vaccines and Vaccination against Lumpy Skin Disease. National Library of Medicine, National Centre for Biotechnology Information doi: 10.3390/vaccines9101136
Lumpy Skin Disease: Aetiology Epidemiology Diagnosis Prevention and Control. (2017) References World Organisation for Animal Health (WOAH) https://www.woah.org/app/uploads/2021/03/lumpy-skin-disease.pdf