Recently, the outbreak of Lumpy skin disease (LSD) in our country especially, in Gujarat and other neighbouring states cause a panic to the dairy farmer communities. The LSD was first reported in Zambia in 1929, and for several years it was not reported outside the African continent. But in 1989, it was first reported outside the African countries i.e., in Israel and then in several countries. In India, LSD was first reported in 2019 in Odisha. LSD is a contagious disease which is a serious concern for the dairy farmers because the milk production is decrease significantly in infected animals. It causes a huge economic loss to dairy farmers. The virus is not deadly due to its low mortality rate below 10%, however morbidity rate is high 5 to 45%. The economy of the farm is affected severely. The LSD is not only affecting the economics of the farm but also the reproductive performance of the farm animals.
The incubation period of the disease is between 4 to 14 days post-infection. The infected animal develops large, firm, slightly raised, circumscribed skin nodules of around 2 to 7 cm in diameter (figure). These nodules are seen over the surface of the body (neck, legs, tail, back, etc.), characterized by a high fever of around 41°C. The mammary gland/ udder, teats, uterus, vagina, muzzle, and nasal cavity are also affected. The necrosis lesion, edema, and congestion are reported in different parts of the gastrointestinal tract. The infected animals show the signs of anorexia, emaciation, nasal discharge, salivation, lachrymation, enlarged lymph nodes, a significant reduction in milk yield, loss of body weight, and death.
Some of the important observations reported in experimentally intradermal inoculation of the virus: -
- 1 – 3 cm nodules at the site of inoculation after 4 to 7 days post-infection
- Viremia and shedding of the virus via oral and nasal discharge after 6 to 18 days post-infection
- Regional lymphadenopathy and development of generalized skin nodules after 7 to 19 days post-infection
- The presence of virus in semen 42 days after the occurrence of fever.
Viability of the virus
The virus can be viable for months in animal sheds and feed stores (dark environments). However, it can be inactivated at 55°C for 2 hours and 65°C for 30 min, it is also susceptible to highly alkaline pH, chloroform, formalin, phenol, and sodium hypochlorite. The virus remains viable for 35 days in desiccated skin crusts, necrotic tissue for 33 days, and air-dried hides for about 18 days. The virus can also be destroyed in Sunlight and lipid detergents. When the skin nodules were kept at – 80°C, the virus was found to be very stable when recovered after 10 years and after 6 months from infected tissue culture fluid kept at 4°C.
Vulnerable animals (cattle)
The immune-compromised cattle are more susceptible to infection and severity. Lactating animals or high-producing animals are susceptible. The young calves are susceptible and develop the nodules within 24 to 48 hours of infection. The weak and sick animals are prone to death from this disease.
Body weight loss
The lack of appetite in the infected animal cause loss of weight. Emaciated, prone to secondary bacterial infections. The affected areas of the body (nodules) infected by secondary bacterial infection, if not treated may lead to severe conditions and death. The loss of body weight impacts the productive performances of the animals and the market value of the animals.
The reproductive capacity of the animals?
The mortality rate of the disease is low but it can cause infertility in infected animals after recovery. Abortion, anoestrus, and lack of ovarian activity are reported that can lead to a huge loss for the dairy farmers. The virus can be found in all secretion including the semen. The infected bull cannot be used for more than a month until complete recovery that affect the production of frozen semen doses for artificial insemination.
Transmission of the virus
The disease is transmitted via non-vector and vector transmission.
Vector transmission: - Several blood-sucking ticks, mosquitoes, and flies can transmit the virus from infected animals to non-infected animals. The virus can spread short distances but these insects or flies can cover longer distances and can amplify the spread of the disease to neighbouring villages, states, and even transboundary transmission.
Non-vector transmission: - non-vector transmission can be direct or indirect. The virus can transmit through body discharges or secretion e.g., via oral, nasal, ocular, milk, semen, and Slough-out infected tissues to non-infected cattle. The intrauterine transmission of the virus is also suspected. This type of transmission is direct transmission. The indirect transmission can be through needles, farm utility materials, or infected fomites to other cattle. The movement of animals between states and countries carries the virus into new areas where the LSD outbreak is not reported yet.
Season: - The population of the vector is more during the monsoon season, and high humidity is a good environment for the vector’s multiplication, therefore, the disease spread quickly through the vectors during the summer and spring or monsoon than in other seasons.
How do I know that the animals suffering from LSD
It is characterized by high fever, development of skin nodules, and lack of appetite. If the neighbouring areas reported an outbreak of LSD, then a high risk to spread to the neighbouring areas quickly. Similar, signs and symptoms may be seen in other diseases of cattle, it should be validated by a veterinary clinician. When there is an outbreak of LSD, preventive measures should be taken as soon as possible to prevent the spread of the disease to other areas.
The virus remains variable in the cattle shed or in a dark environment. The cattle shed should be cleaned regularly with proper disinfection. New animals from outside should not be introduced to the farm. Maintenance of hygiene. Protect the animals from blood-sucking insects using a mosquito net. The movement of the animals from village to village or state or country should be prevented. The feed material brought from various locations should be handled carefully. Proper disposal of the infected carcass, washing with the disinfectant of contaminated premises, use of pest repellents, and strict quarantine are essential to minimize the spread of disease. The vaccination is the only suitable preventive measure to protect the animals.
Vaccination against LSD is only way to control the disease. Vaccination provides immunity or protection against the LSD that prevents severe economic loss to dairy sector. However, the countries which have not reported any cases of LSD is not advisable for vaccination. The homologues live attenuated virus vaccination provides a good immunity for up to 3 years. However, heterologous live attenuated vaccines i.e., Sheep or goat pox vaccine also be carried out against LSD. The Lumpy skin disease virus, sheep pox virus and the goat pox virus are from the same family i.e., Poxviridae, therefore, the heterologous live attenuated vaccines can be used. The Indian Council of Agricultural Research recently developed live attenuated homologous vaccine against the disease. The availability and commercialization are essential to control the LSD in India. Along with the vaccination awareness among the farmers is also important.
The lumpy skin disease can (LSD) damages the economy of the dairy farm significantly. The skin nodules which are the characteristics of this disease impact the quality of the hide quality. The secondary bacterial infection in infected tissue increases the cost of treatment. Further, the infertility problem of the infected animals leads to severe consequences after recovering from LSD. The prevention and control of disease are essential to prevent the dairy sector from economic loss and the death of animals. Therefore, vector control measures, vaccination, and awareness program are necessary.