House flies (Musca domestica) and little house flies (Fannia canicularis) were examined for their ability to take up and harbor a velogenic strain of exotic Newcastle disease virus (ENDV) (family Paramyxoviridae, genus Avulavirus). Laboratory-reared flies were allowed to feed on evaporated milk containing ENDV at a virus concentration of 108.3 egg infectious dose (EID)50/0.1 ml or on poultry feces containing an ENDV titer of 105.8 EID50/0.1 g. Flies exposed to either infectious food source for 24 hr became transiently infected with virus. Virus persisted predominantly in the mid- and hindgut, with relatively little virus isolated from the remainder of the fly body. Virus persisted similarly in both fly species that were fed evaporated milk containing ENDV, with a maximum ENDV titer of 105.98 EID50/fly for the house fly and 10 4.78 EID50/fly for the little house fly at 1 day postexposure; titers decreased on subsequent days to 102.38 EID 50/fly for house fly and ≥1 EID50/fly for little house fly at 5 days postexposure. Both fly species acquired viral titers greater than the infective dose for a susceptible chicken (103.0 EID 50-104.0 EID50). In addition, flies fed evaporated milk containing a high titer of ENDV maintained viral titers above the infective dose for up to 4 days postexposure to the infectious food source. Flies fed on infective feces retained a chicken infective dose for only one day. The decrease in viral titer over time was significantly explained by logistic regression for both fly species (P < 0.05). The slope of the regression line was not different for the two fly species (P < 0.05), indicating a similar rate of virus loss.
- Mechanical vector
- Newcastle disease virus