Demonstration of lumpy skin disease virus infection in Amblyomma hebraeum and Rhipicephalus appendiculatus ticks using immunohistochemistry.

Lumpy skin disease (LSD) is caused by lumpy skin disease virus (LSDV), a member of the genus Capripoxvirus. Transmission of the virus has been associated with haematophagous insects such as Stomoxys calcitrans as well as Aedes and Culex species of mosquitoes. Recent studies have reported the transmission of the virus by Amblyomma hebraeum, Rhipicephalus appendiculatus, and Rhipicephalus decoloratus ticks and the presence of LSDV in saliva of A. hebraeum and R. appendiculatus ticks. The aim of this study was to determine which tick organs become infected by LSDV following intrastadial infection and transstadial persistence of the virus in A. hebraeum and R. appendiculatus ticks. Nymphal and adult ticks were orally infected by feeding them on LSDV-infected cattle. Partially fed adult ticks were processed for testing while nymphs were fed to repletion and allowed to moult to adults before being processed for testing. The infection in tick organs was determined by testing for the presence of the viral antigen using monoclonal antibodies with immunohistochemical staining. The viral antigen was detected in salivary glands, haemocytes, synganglia, ovaries, testes, fat bodies, and midgut. Since the virus was shown to be able to cross the midgut wall and infect various tick organs, this may indicate potential for biological development and transmission of LSDV in ticks. This study strengthens the previously reported evidence of the occurrence of LSDV in tick saliva.

Transovarial passage and transmission of LSDV by Amblyomma hebraeum, Rhipicephalus appendiculatus and Rhipicephalus decoloratus.

Lumpy skin disease (LSD), an acute, sub-acute or inapparent disease of cattle, is caused by lumpy skin disease virus (LSDV), a member of the genus Capripoxvirus in the family Poxviridae. LSD is characterised by high fever, formation of circumscribed skin lesions and ulcerative lesions on the mucous membranes of the mouth, respiratory and digestive tracts. It is an economically important disease due to the permanent damage to hides, the reduction in productivity and trade restrictions imposed on affected areas. Transmission has been associated with blood-feeding insects such as stable flies (Stomoxysis calcitrans) and mosquitoes (Aedes aegypti). Mechanical (intrastadial) and transstadial transmission by Amblyomma hebraeum and Rhipicephalus appendiculatus as well as transovarial transmission by R. decoloratus have been reported. In this study transovarial passage of LSDV to larvae and subsequent transmission to recipient animals were demonstrated. The finding of transovarial passage of LSDV in female ticks shows the potential for A. hebraeum, R. appendiculatus and R. decoloratus to be reservoir hosts for LSDV.

Evidence of vertical transmission of lumpy skin disease virus in Rhipicephalus decoloratus ticks.

Lumpy skin disease (LSD) is an economically important acute or sub-acute disease of cattle that occurs across Africa and in the Middle East. The aim of this study was to assess whether Rhipicephalus decoloratus ticks were able to transmit lumpy skin disease virus (LSDV) transovarially. Uninfected, laboratory-bred R. decoloratus larvae were placed to feed on experimentally infected "donor" cattle. After completion of the life cycle on donor animals, fully engorged adult female ticks were harvested and allowed to lay eggs. Larvae that hatched from these eggs were then transferred to feed on uninfected "recipient" cattle. The latter became viraemic and showed mild clinical disease with characteristic skin lesions and markedly enlarged precrural and subscapular lymph nodes. This is the first report of transovarial transmission of poxviruses by R. decoloratus ticks, and the importance of this mode of transmission in the spread of LSDV in endemic settings requires further investigation.