Replication and dissemination of Rift Valley fever virus in Culex pipiens.

Abstract Following ingestion of 104.2 to 107.2 plaque-forming units (PFU) of Rift Valley fever (RVF) virus, 662 of 850 female Culex pipiens (78%) became infected. Those mosquitoes that became infected separated into two distinct groups: 1) those with a non-disseminated infection limited to the gut, and 2) those with a disseminated infection. The former group contained a median of 103.2 PFU, while those females with a disseminated infection contained a median of 105.5 PFU. Only those females with a disseminated infection contained a median of 105.5 PFU. Only those females with a disseminated infection were capable of transmitting virus by bite to a susceptible hamster. This is consistent with a mesenteronal escape barrier to viral dissemination. Following intrathoracic inoculation of RVF virus, all females developed a disseminated infection (26/26) and successfully transmitted virus by bite (49/49) if allowed to feed on a susceptible hamster or suckling mousc. Examination of legs and bodies separately provided a rapid and efficient method of determining dissemination status.