Objective—To evaluate retention of porcine reproductive
and respiratory syndrome virus (PRRSV) in
houseflies for various time frames and temperatures.
Sample Population—Fifteen 2-week-old pigs,
two 10-week-old pigs, and laboratory-cultivated
Procedure—In an initial experiment, houseflies were
exposed to PRRSV; housed at 15°, 20°, 25°, and 30°C;
and tested at various time points. In a second experiment
to determine dynamics of virus retention,
houseflies were exposed to PRRSV and housed
under controlled field conditions for 48 hours.
Changes in the percentage of PRRSV-positive flies
and virus load per fly were assessed over time, and
detection of infective virus at 48 hours after exposure
was measured. Finally, in a third experiment, virus
loads were measured in houseflies allowed to feed on
blood, oropharyngeal washings, and nasal washings
obtained from experimentally infected pigs.
Results—In experiment 1, PRRSV retention in houseflies
was proportional to temperature. In the second
experiment, the percentage of PRRSV-positive houseflies
and virus load per fly decreased over time; however,
infective PRRSV was found in houseflies 48 hours
after exposure. In experiment 3, PRRSV was detected in
houseflies allowed to feed on all 3 porcine body fluids.
Conclusions and Clinical Relevance—For the conditions
of this study, houseflies did not support PRRSV
replication. Therefore, retention of PRRSV in houseflies
appears to be a function of initial virus load after ingestion
and environmental temperature. These factors
may impact the risk of insect-borne spread of PRRSV
among farms. (Am J Vet Res 2005;66:1517–1525)