Lumpy skin disease

Lumpy skin disease (LSD) is an infectious disease in cattle caused by a virus of the family Poxviridae, also known as Neethling virus. The disease is characterized by fever, enlarged superficial lymph nodes and multiple nodules (measuring 2–5 cm in diameter) on the skin and mucous membranes (including those of the respiratory and gastrointestinal tracts). Infected cattle also may develop edematous swelling in their limbs and exhibit lameness. The virus has important economic implications since affected animals tend to have permanent damage to their skin, lowering the commercial value of their hide. Additionally, the disease often results in chronic debility, reduced milk production, poor growth, infertility, abortion, and sometimes death. Onset of fever occurs almost one week after infection by the virus. This initial fever may exceed 41 °C and persist for one week. At this time, all of the superficial lymph nodes become enlarged. The nodules, in which the disease is characterized by, appear seven to nineteen days after virus inoculation. Coinciding with the appearance of the nodules, discharge from the eyes and nose becomes mucopurulent. The nodular lesions involve the dermis and the epidermis, but may extend to the underlying subcutis or even to the muscle. These lesions, occurring all over the body (but particularly on the head, neck, udder, scrotum, vulva and perineum), may be either well-circumscribed or they may coalesce. Cutaneous lesions may be resolved rapidly or they may persist as hard lumps. The lesions can also become sequestrated, leaving deep ulcers filled with granulation tissue and often suppurating. At the initial onset of the nodules, they have a creamy grey to white color upon cut section, and may exude serum. After about two weeks, a cone-shaped central core of necrotic material may appear within the nodules. Additionally, the nodules on the mucous membranes of the eyes, nose, mouth, rectum, udder and genitalia quickly ulcerate, aiding in transmission of the virus. In mild cases of LSD, the clinical symptoms and lesions are often confused with Bovine Herpesvirus 2 (BHV-2), which is, in turn, referred to as pseudo-lumpy skin disease. However, the lesions associated with BHV-2 infections are more superficial. BHV-2 also has a shorter course and is more mild than LSD. Electron microscopy can be used to differentiate between the two infections. BHV-2 is characterized by intranuclear inclusion bodies, as opposed to the intracytoplasmic inclusions characteristic of LSD. It is important to note that isolation of BHV-2 or its detection in negatively-stained biopsy specimens is only possible approximately one week after the development of skin lesions. Lumpy skin disease virus (LSDV) is double-stranded DNA virus. It is a member of the capripoxvirus genus of Poxviridae. Capripoxviruses (CaPVs) represent one of eight genera within the Chordopoxvirus (ChPV) subfamily. The capripoxvirus genus consists of LSDV, as well as sheeppox virus, and goatpox virus. CaPV infections are usually host specific within specific geographic distributions even though they are serologically indistinguishable from one another. Like other viruses in the Poxviridae family, capripoxviruses are brick-shaped. Capripoxvirus virions are different than orthopoxvirus virions in that they have a more oval profile, as well as larger lateral bodies. The average size of capripoxvirions is 320 nm by 260 nm. The virus has a 151-kbp genome, consisting of a central coding region which is bounded by identical 2.4 kbp-inverted terminal repeats and contains 156 genes. There are 146 conserved genes when comparing LSDV with chordopoxviruses of other genera. These genes encode proteins which are involved in transcription and mRNA biogenesis, nucleotide metabolism, DNA replication, protein processing, virion structure and assembly, and viral virulence and host range. Within the central genomic region, LSDV genes share a high degree of collinearity and amino acid identity with the genes of other mammalian poxviruses. Examples of viruses with similar amino acid identity include suipoxvirus, yatapoxvirus, and leporipoxvirus. In terminal regions, however, collinearity is interrupted. In these regions, poxvirus homologues are either absent or share a lower percentage of amino acid identity. Most of these differences involve genes that are likely associated with viral virulence and host range. Unique to Chordopoxviridae, LSDV contains homologues of interleukin-10 (IL-10), IL-1 binding proteins, G protein-coupled CC chemokine receptor, and epidermal growth factor-like protein, which are found in other poxvirus genera. LSDV mainly affects cattle and zebus, but has also been seen in giraffes, water buffalo, and impalas. Fine-skinned Bos taurus cattle breeds such as Holstein-Fresian and Jersey are the most susceptible to the disease. Thick-skinned Bos indicus breeds including the Afrikaner and Afrikaner cross-breeds show less severe signs of the disease. This is probably due to the decreased susceptibility to ectoparasites that Bos indicus breeds exhibit relative to Bos taurus breeds. Young calves and cows at peak lactation show more severe clinical symptoms, but all age-groups are susceptible to the disease.