LUMPY SKIN DISEASE (LSD)- A brief know-how
Mudasir Ahmad Shah*1 and Safoora Kashafi1
- Veterinary Assistant Surgeon, Department of Animal Husbandry, Kashmir
*Corresponding author: Mudasir Ahmad Shah; Email: syedmudasirshah907@gmail.com
Introduction
Lumpy skin disease, an infectious viral disease of ruminants is caused by Lumpy Skin Disease Virus (LSDV) of genus: Capri-poxvirus, subfamily: Chordo-poxvirniae and family: Poxviridae. The disease is known by different names such as “LSD”, “Pseudo-urticaria” and “Neethling virus disease”. LSD is a non-zoonotic, vector borne and transboundary disease with limited host range and currently restricted to ruminants viz. cattle and water buffaloes. The disease is endemic in African countries and has recently been reported in European and Asian countries including India. Due to its substantial economic impact through the loss of animals, decresed productivity, loss of export markets, threat to the international trade, potential for rapid spread, the cost of control and prevention campaigns, the World Organization for Animal Health (OIE) has placed this transboundary disease on the Notifiable Disease List. The LSD virus can be abused as an economic bioterrorism agent (agro-terrorism). The disease is associated with high morbidity but low mortality (1-2%).
Transmission and spread
Susceptible hosts contract the virus principally by mechanical means from hematophagous arthropods including biting flies, mosquitoes and ticks. Ticks act as mechanical vectors and reservoirs of virus. The disease incidences significantly increase with the onset of seasonal rains during summer season due to peak activity of the vectors and the incidences decrease significantly with the onset of winters. The evidence of direct transmission of LSDV is scarce. Virus is secreted in milk, nasal secretions, saliva, blood and lacrymal secretions which acts as indirect source of infection for animals sharing feeding space, watering troughs and grazing collectively. Affected free-ranging cattle can also be a source for rapid spread of LSD. LSD virus transmission through intrauterine route has been documented as well and the infection has been found to be transmitted from infected mother to calf via milk secretions. Virus persists in the semen for up to 42 days post-infection and can be a source of venereal transmission. Iatrogenic route can be another route of spread of virus when a single needle is used for mass vaccination that can acquire the virus from the skin scabs or crusts. Skin lesions also act as a major source of infection.
Spread of LSD in India
Following outbreaks in the Middle East and Europe, LSD also made its entry into Asia. In recent years, LSD has been reported from neighbouring countries of India viz. China and Bangladesh. The disease had first emerged in Bangladesh in July 2019. India had also witnessed the cases in 2019 in eastern states, especially West Bengal and Odisha. But this year, the disease has been reported in western and northern states as well as in Andaman and Nicobar. The reasons of the disease spread to India are unknown but it may be due to livestock movement across international borders or may be due to vector movement from the neighbouring countries. Though Lumpy Skin Disease is spreading at a rapid pace in India, it does not spread to humans, even if they are in contact with sick cattle that have been diagnosed with LSD.
Types of animals affected
Cattle breeds of both sexes and all ages are susceptible to LSDV, but young calves, lactating cows and underweight animals are more susceptible to natural infections due to impairment of humoral immunity. Indigenous cattle breeds are more resistant as compared to exotic cattle breeds. It has been found that animals that have recovered from natural infection by the virus show lifelong immunity. Calves born from infected dams are resistant to clinical disease approximately for a period of 6 months, because of the acquired maternal antibodies. Affected animals clear the infection with no carrier state.
Signs and symptoms observed in affected animals
The symptoms of LSD in cattle range from mild to severe characterized by raised body temperature (1050F), inappetence, nasal discharge, salivation, lacrymation, multiple skin nodules that are 2–7 cm in diameter spreading over the neck, back, perineum, tail, limbs and the mucous membranes of respiratory & urogenital systems. The lesions develop within 2 to 5 weeks of infection in naturally infected animals and may involve subcutaneous tissues, musculature and internal organs. Affected animals also exhibit lameness, emaciation, drastic reduction in milk production, lymphadenitis and sometimes may die. Pneumonia is a common sequel in animals with lesions in the mouth and respiratory tract. The animal falls in a vicious cycle as it loses stamina due to loss of appetite. Edema may develop in limbs and in brisket region. Skin nodules may persist as hard lumps or become moist, necrotic, and slough or ulcerate. Lesions where skin is lost may remain visible for long periods and when lesions coalesce, large areas of raw tissue can be exposed which become susceptible to invasion with screwworm fly larvae. The sloughed away lesion may create a hole of full skin thickness and characteristic lesion of “inverted conical zone” of necrosis known as “sit fast”. Severe cases of LSD are highly characteristic and easy to recognize, but early stages of infection and mild cases may be confusing with other diseases affecting the skin. For instance Pseudo lumpy skin disease caused by bovine herpes virus-2 (BHV) has circular superficial lesions which may cover the entire body and up to 2 cm in diameter. It has distinctive intact central area and raised edges, accompanied by loss of hair. Urticaria, Streptotrichosis, Ringworm, Hypoderma bovis infection, Photosensitization, Bovine papular stomatitis, Foot and mouth disease, Bovine viral diarrhea, and Malignant catarrhal fever are all considered as differential diagnosis of LSD.
Risk factors
The major factors associated with the spread of LSD include a warm and humid climate, conditions supporting an abundance of vector populations such as those seen after seasonal rains, and the introduction of new animals to a herd. The other risk factors which may increase the disease prevalence include transport of infected animals into disease-free areas, sharing of pastures and water sources, and the direction and strength of wind.
Diagnosis
Despite a primary clinical diagnosis of LSD several highly sensitive, well-validated, real-time and gel-based PCR methods are available and widely used to detect the presence of CaPV DNA. Electron microscopy examination can also be used for primary diagnostics although it is uncommon. Live virus can be isolated using various cell cultures of bovine or ovine origin. During the outbreaks, most of the infected animals seroconvert and serum samples can be tested using serum/virus neutralization, immunoperoxidase monolayer assay (IPMA) or indirect fluorescent antibody test (IFAT).
Prevention and Control
The recent spread of the disease in disease-free countries indicates the importance of its transmission, as well as control and eradication strategies to be followed. Vaccination is the only effective method to control the disease in endemic areas along with movement restrictions and isolation or removal of the affected animals. The treatment of LSD is only symptomatic and targeted at preventing secondary bacterial complications using a combination of antimicrobials, anti-inflammatory, anti-septic solutions, immune-modulators and other supportives. The culling of affected animals, movement restrictions, compulsory and consistent vaccination has been recommended as control strategies. However, regarding the role of arthropod vectors, elimination of the disease is likely to be difficult and any delays in the removal of infected animals increases the risk of LSD transmission. Moreover, risk factors should be considered in control activities. Furthermore, the rapid confirmation of a clinical diagnosis is essential so that eradication measures, such as quarantine of affected and in-contact animals, proper disposal of carcasses, cleaning and disinfection of the premises, and insect control can be implemented as soon as possible during the disease outbreak. The rigorous import restrictions on livestock, carcasses, hides and semen from endemic areas must be in place in disease-free areas. The commercially accessible vaccines against LSD are live attenuated vaccines which produce a strong and long-lasting immune response and are efficient in the control of disease spread. However, live vaccines can cause local inflammation and a mild disease with skin lesions. Natural infection is probably made worse by the vaccination of infected animals.
Keeping in consideration the disastrous economic impact on the poor farmer community, following measures are suggested to effectively combat the alarming situations created by LSD outbreaks:
- Clinico-hematological and biochemical profile of cattle affected by LSD need to be evaluated in addition to typical clinical signs.
- Accurate on-time diagnosis is needed for control measures.
- Segregation of affected animals from healthy animals.
- Annual vaccination strategy with homologous strain of the LSDV is obligatory in endemic areas.
- Vector control and animal movement restriction during active period of insect movement is important.
- Breeding Bulls need to be diagnosed for LSDV.
- Prohibiting cattle fairs, exhibitions and transportation of cattle in the affected areas.
- Deep burial of animals died due to LSD.
