# Vector competence re-evaluation of reared Glossina palpalis gambiensis for transmission of Trypanosoma congolense and Trypanosoma brucei brucei isolates for an experimental event

## TL;DR

This study updates the ability of a long-reared tsetse fly colony to transmit two types of trypanosomes, finding changes in transmission efficiency over time.

## Contribution

The study provides updated vector competence data for a long-standing tsetse fly colony against specific trypanosome isolates.

## Key findings

- 10.58% of tsetse flies developed mature infections with Trypanosoma congolense, yielding a VC index of 0.106.
- 4.21% of tsetse flies developed mature infections with Trypanosoma brucei brucei, yielding a VC index of 0.042.
- Vector competence for T. congolense was 4.8 times higher than previously reported, suggesting changes due to long-term insectary rearing.

## Abstract

Tsetse flies (Diptera: Glossinidae) are vectors of human and animal trypanosomes. The Glossina palpalis gambiensis Burkina Faso (BKF) colony, established in 1972 and rejuvenated once in 1981, is a long-standing closed colony used extensively for research and vector control. While its performance and competitiveness for sterile insect technique (SIT) programs are regularly monitored, its vector competence (VC) data are outdated. This study aimed to update the VC data of this 47-year-old colony (from the onset of experiment in 2019) against Trypanosoma congolense and T. brucei brucei in laboratory conditions using trypanosome clone and tsetse fly individuals from the BKF colony.

Vector competence was studied by infecting rats with T. congolense IL1180 and T. b. brucei BE8P2P2, on which tsetse flies received their first blood meal. Dissections were subsequently performed at different time intervals.

Following experimental infections with T. congolense IL1180, 10.58% (20/189) of G. p. gambiensis developed mature infections (trypanosomes in the proboscis), resulting in an average VC index of 0.106. For T. b. brucei BE8P2P2, 4.21% (11/261) of flies developed mature infections (trypanosomes in the salivary glands), yielding an average VC index of 0.042.

The VC for T. b. brucei aligned with previous findings from 21 years ago, though a different trypanosome isolate was used at that time. However, using the same trypanosome strain, the observed competence for T. congolense was 4.8 times higher than previously reported. These results raise questions about the long-term effects of insectary rearing on VC, particularly in the absence of prolonged parasite exposure.