Lumpy Skin Disease (LSD) is a viral affliction of cattle and water buffalo that poses a serious threat to livestock industries globally. It is classified as a transboundary animal disease due to its potential for rapid spread across international borders. First identified in Zambia in 1929, the virus has since expanded its geographical reach, moving out of its historical range in Africa to affect the Middle East, the Balkans, Russia, and the Asian subcontinent. Understanding this disease is crucial for farmers, veterinarians, and regulatory bodies worldwide.
Viral Characteristics and Clinical Signs
The Lumpy Skin Disease Virus (LSDV) belongs to the genus Capripoxvirus within the Poxviridae family. This virus is characterized by a large, double-stranded DNA genome and is closely related to the viruses that cause sheep pox and goat pox. The host range is highly specific, primarily affecting cattle and water buffalo, though some wild ruminants have also been reported to be susceptible.
Infected animals initially develop a high fever, often exceeding 40°C, accompanied by depression and a reluctance to eat. Within five to seven days, the most distinctive clinical signs appear: multiple, firm, raised skin nodules ranging from 0.5 to 5 centimeters in diameter. These lesions are commonly found on the head, neck, limbs, udder, and genitals, involving the dermis and epidermis.
The nodules can either regress or progress to form a central core of necrotic tissue, known as a “sit-fast,” which eventually sloughs off, leaving deep ulcers. These open sores are prone to secondary bacterial infections, complicating the disease course. Other common symptoms include a marked reduction in milk yield, swelling of the limbs and brisket (edema), enlarged superficial lymph nodes, and mucopurulent discharge from the eyes and nose.
Methods of Transmission
Transmission of the Lumpy Skin Disease Virus occurs predominantly through mechanical means, primarily involving blood-feeding arthropods. Insects such as biting flies, mosquitoes, and ticks act as mechanical vectors, transferring the virus from an infected animal to a susceptible one. The virus does not undergo a reproductive cycle within the insect; rather, it is carried on the mouthparts and introduced during a subsequent feeding.
The abundance of these vectors, particularly in warm and humid environments, is a major factor in the rapid, short-distance spread of the disease during an outbreak. Studies have demonstrated that certain tick species, such as Rhipicephalus appendiculatus, can mechanically transmit the virus even when feeding on viraemic animals.
Direct contact with an infected animal plays a less significant role in transmission compared to insect vectors, but it is still a recognized route. The virus is shed in various bodily fluids, including saliva, nasal and ocular secretions, and semen. Indirect spread can happen when susceptible animals come into contact with contaminated equipment, feed, or water troughs, as the virus is highly stable and can survive for prolonged periods in dried scabs and the environment.
Disease Management and Prevention Protocols
Large-scale regional vaccination of cattle and water buffalo is considered the most effective tool for minimizing production losses and halting the spread of the virus in endemic and newly affected regions. Live attenuated vaccines are the main type available, with the Neethling strain being the most widely used homologous vaccine for cattle, offering good protection. These vaccines reduce the population of susceptible animals, thereby preventing the entry and spread of the disease.
Movement control measures are a necessary component of disease management, especially in areas with recent outbreaks. This involves strict quarantine of infected and exposed herds and restricting the movement of animals and potentially contaminated materials like hides and semen. The movement of seemingly healthy animals incubating the virus is a significant driver of long-distance, transboundary spread.
Vector control strategies focus on reducing the population of biting insects through the use of insecticides and environmental management. Reducing standing water and manure accumulation can limit breeding sites for mosquitoes and flies, thereby decreasing the mechanical transmission risk.
There is no specific antiviral treatment for LSDV, so management relies on supportive care for affected animals. This care includes pain management, fluid therapy to combat dehydration, and the use of antibiotics to prevent or treat secondary bacterial infections that commonly develop in the open skin ulcers. Early detection and rapid implementation of biosecurity measures, alongside vaccination, are crucial for effective outbreak control.
Economic and Trade Implications
Lumpy Skin Disease is formally listed as a notifiable disease by the World Organisation for Animal Health (WOAH), formerly OIE, due to the substantial financial consequences of outbreaks. The economic losses are multifaceted, stemming directly from the impact on animal health and indirectly from trade disruption.
Production losses are significant, including:
- A sharp decrease in milk yield, which can fall by 10% to 85% in affected herds.
- Weight loss and chronic debility.
- Temporary or permanent infertility in both sexes.
- Hide damage due to the extensive scarring from the skin nodules.
These factors reduce the commercial value of livestock and their products. Outbreaks trigger substantial costs for control measures, such as mass vaccination campaigns and the culling of severely diseased animals. Internationally, the WOAH listing mandates reporting, which often leads to trade bans and restrictions on the movement of live cattle and their products from affected countries. These trade limitations impede economic growth for countries reliant on the export of cattle and related commodities.