Mechanical transmission of Trypanosoma brucei rhodesiense by Glossina morsitans morsitans (Diptera:Glossinidae)

Abstract

Interrupted feedings of teneral, laboratory-reared Glossina morsitans morsitans were used to study mechanical transmission of Trypanosoma. brucei rhodesiense. Intervals between exposure of individual flies on parasitaemic rats and refeeding on clean rats were varied from five minutes to 24 hours. Direct transmissions were demonstrated at each interval up to 160 minutes after exposure. Proboscis dissections showed that active trypanosomes were present up to 320 minutes after exposure. No mechanical transmissions from bovine to bovine occurred in 39 attempts, when groups of20–120 flies exposed on parasitaemic bovines were transferred immediately to uninfected cattle, but two of 40 individual flies exposed on parasitaemic bovines mechanically transmitted trypanosomes to clean rats. Proboscis dissections made immediately after flies were exposed to a bovine with a parasitaemia of 4·8 × 10⁴ trypanosomes/μl of blood showed that 11 of 20 (55%) had active trypanosomes in the food canal. The mean number of trypanosomes per proboscis was 29·4 (± 20·5). Of 20 flies exposed on a bovine with a low parasitaemia, however, only one trypanosome was seen in proboscis dissections. The parasitaemia of the infected donor was an important factor in mechanical transmission. The mechanical transmission of trypanosomes from one host to another may largely depend on the infectivity threshold of the recipient host, and individual mechanically-infected tsetse flies may not transmit an infective dose.