The barriers to bluetongue virus infection, dissemination and transmission in the vector, Culicoides variipennis (Diptera: Ceratopogonidae)

Abstract

Transmission of bluetongue virus (BTV) by a vector species of Culicoides was studied using immunohistochemistry, virus titration and in vitro transmission tests. Adult female C. variipennis were used from two colonies that are either "transmission competent" or "transmission refractory" after oral infection with BTV. Intrathoracic (i.t.) injection of BTV into the haemocoel always resulted in a fully disseminated infection and transmission of virus in saliva. However, after ingestion of an infectious blood meal, only 30% (approximately) of midges from either colony became persistently infected. Although none of the orally infected insects from the "refractory" colony were able to transmit virus, 12% of those from the "competent" colony (containing > or = 10(3.0)TCID50 of virus/midge) did transmit BTV in their saliva. The most important barriers to BTV transmission in Culicoides vector species appeared to be a mesenteron infection barrier (MIB), which controls initial establishment of persistent infection, a mesenteron escape barrier (MEB) which can restrict virus to gut cells and a dissemination barrier (DB) which can prevent virus which enters the haemocoel from infecting secondary target organs. Culicoides variipennis do not appear to present either a salivary gland infection barrier (SGIB), or a salivary gland escape barrier (SGEB) to BTV.

Drosophila melanogaster as a Model Organism for Bluetongue Virus Replication and Tropism

“…Furthermore, this virus was found to replicate efficiently in vivo in D. melanogaster after removal of W. pipientis infections by treatment with tetracycline. Finally, confocal analysis revealed that, similar to what has been observed in its insect vector (26), BTV replicates in the fat bodies, salivary glands, and proventriculi (foregut-midgut junction) of infected D. melanogaster flies.…”

“…These data imply that BTV can enter from the basement membrane (e.g., membrane directly in contact with the hemocoel) of foregut cells but not midgut cells. Besides BTV, several other pathogenic arboviruses, including Venezuelan equine encephalitis virus and West Nile virus, have been shown to infect the foregut-midgut junction of their insect vectors (26,29,68). Therefore, infection of this organ may play a major role in the replication cycle of BTV in insects.…”

A possible overwintering mechanism for bluetongue virus in the absence of the insect vector FN1

“…These BTVinfected cd T-cell cultures grow continuously, with no obvious CPE. A similar persistent infection of BTV has been demonstrated in some insect cell cultures without shut-off of host cell DNA or protein synthesis (Jennings & Boorman, 1979;Wechsler et al, 1989;Fu et al, 1999) where there was also little or no sign of CPE.…”

Seasonal Transmission of Bluetongue Virus by <I>Culicoides sonorensis</I> (Diptera: Ceratopogonidae) at a Southern California Dairy and Evaluation of Vectorial Capacity as a Predictor of Bluetongue Virus Transmission

“…Midges were sorted by sex and females were further sorted by parity status (Dyce 1969, Potter and Akey 1978, Akey and Potter 1979. Transovarial transmission of BLU virus by C. sonorensis has not been shown (Jones and Foster 1971a, Fu et al 1999, and therefore only parous females would be expected to have acquired BLU virus.…”