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Title: The persistence of African swine fever virus in the argasid tick Ornithodoros moubata.
Author: Rennie, Louise Frances.
Awarding Body: University of Herfordshire
Current Institution: University of Hertfordshire
Date of Award: 1998
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African swine fever virus (ASFV) usually causes a fatal haemorrhagic disease in domestic pigs. However ASFV has no apparent adverse effects on its vertebrate reservoir hosts, warthogs (Phacochoerus aethiopicus) and bushpigs (Potamochoerus porcus). The virus is maintained in the wild by a campestral cycle between wild members of the family Suidae, especially warthogs, and the argasid ticks which inhabit their burrows. Infection of Ornithodoros moubata with the VIC T90/1 or LIV 13/33 isolate of ASFV did not have an adverse effect on the oviposition rates of infected female ticks. Hatching rates of eggs laid by infected females were also unaffected. In addition infection with ASFV did not cause a significant reduction in the feeding and moulting rates of first nymphal stage ticks from infected females. The feeding rates of adult ticks infected with either of the two isolates of virus were also unaffected. However, infected adult ticks showed an increase in mortality rates over uninfected ticks. After the second blood meal 40.0% of ticks infected with the VIC T901l isolate of ASFV died and 33.3% of ticks infected with LIV 13/33 died, whereas only 4.0% ofuninfected ticks died. Similarly after the third blood meal 93.3% of ticks infected with the VIC T901l isolate of ASFV died and 84.2% of ticks infected with LIV 13/33 died whereas 9.1% ofuninfected ticks died. ASFV is capable of being passed transovarially and transstadially within the Pirbright colony of O. moubata. Filial infection rates were highly variable between individual ticks. After the second blood meal filial infection rates ranged from 1.8% to 31.8% for ticks infected with the VIC T90/1 isolate of ASFV and from 1.2% to 35.5%. After the third blood meal filial infection rates ranged from 15.0% to 32.4% and 1.7% to 44.0% respectively. An increase in the number of blood meals increased the number of females capable of laying infected eggs and increased the filial infection rates of these females. Transstadially infected individual second nymphal stage ticks were capable of excreting up to 104 . sHADsoitick, which is sufficient to infect a pig or warthog. Dissemination and localisation of ASFV within the tick vector was monitored by using anindirect immunoperoxidase staining technique. In ticks which had been infected either orally or by direct inoculation of virus into the haemocoel, viral antigen was detected first in the sexual organs of both male and female ticks. When comparing orally infected ticks and ticks infected by direct inoculation of virus into the haemocoel, the rate at which the various organs become infected did not differ substantially. Furthermore, since infection of ticks either by inoculation of virus directly into the haemocoel (bypassing the gut) or by oral ingestion of virus, resulted in similar infection rates in the organs in the organs (31.7% and 31.0% respectively). It seems unlikely that 0. moubata possesses a gut barrier to ASFV
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Veterinary sciences & veterinary medicine Veterinary medicine Microbiology