Improving SIT for Tsetse Flies through Research on their Symbionts and Pathogens

The CRP has resulted in some important achievement which will help in improving the tsetse mass production for SIT program. These achievements include the following:

1-Decipher host-symbiont interactions to understand tsetse’s nutritional ecology and improve mass rearing procedures:
i- Developed the methodology to generate fertile tsetse lines without symbionts through dietary supplementation,
ii- Obtained Knowledge on the functional role of Wigglesworthia in tsetse symbiosis.

2-Investigate tsetse pathogen interactions to improve tsetse control:
see 4 below.

3-Study the population dynamics of tsetse microbial flora:
i- Discovered varying Sodalis genotypes in natural populations,
ii- Observed correlation of Sodalis occurrence with parasite infection in natural populations.

4-To understand and manage tsetse virus interactions in laboratory populations
a. DNA database for virus populations identified:
i- identified and characterized the causal agent (SGHV) of salivary gland hypertrophy,
ii- sequenced, annotated, and published genomes of three SGHVs (two strains of GpSGHV and one strain of MdSGHV),
iii- classified a novel virus family (Hytrosaviridae) with two genera (Glossinavirus and Muscavirus), accepted by the ICTV; proposed that hytroviruses are related phylogenetically with baculoviruses and nudiviruses,
iv- genomic sequence provided a framework to:
- developed specific and universal PCR primers to detect virus in field and laboratory tsetse colonies,
- identified genes that are stable, essential, and suitable candidates for the development of antiviral therapies,
- identified antiviral dsRNAs for RNAi suppression of viral replication,
- evaluated the level of GpSGHV genetic diversity in field and laboratory tsetse fly populations,
- determined the SGHV proteomes and identified targets for the development of antibodies to suppress viral infection.

b. Transmission mode of tsetse SGHV determined:
i- recognized that in field populations the primary mode of transmission is vertical whereas in colonies horizontal transmission also occurs and that infected flies secrete the virus during membrane feeding,
ii- utilized PCR-based detection tools and showed that tsetse colonies with low prevalence of SGH symptoms (approx. 5%) harbour high levels (80-100%) of asymptomatic infections, iii- determined (by qPCR) that asymptomatic flies (i.e., infected flies that do not show SGH symptoms) contain variable levels of GpSGHV,
iv- discovered that in colonies, membrane feeding facilitates horizontal virus transmission resulting in infected F1 progeny.

c. SGH symptom free colonies maintained:
partially achieved,
i- discovered that the tsetse fly virus exists in both an asymptomatic and symptomatic state whereas the house fly virus expresses only symptomatic infections,
ii- associated symptomatic GpSGHV infection with reduced fertility of both sexes,
iii- surveyed field populations throughout Africa to determine the prevalence of both symptomatic (by dissection) and asymptomatic (by PCR) infections in flies; prevalence determined by PCR varied widely (0-90%) among and within different Glossina spp,
iv- designed and tested different strategies to manage virus levels in tsetse colonies: clean feeding (i.e., fresh blood membranes are used for each feeding), RNAi, polyclonal antibodies, oligopeptides, and antiviral drugs; each of these strategies reduced virus loads to varying degrees,
v- found that integrating several strategies (such as clean feeding and antiviral drugs) eliminated symptomatic infections and significantly reduced the levels of asymptomatic infections in tsetse colonies.

5-Develop parasite refractory lines:
partially achieved because of the inability to efficiently transmit Sodalis between generations, nevertheless, we have:
i- identified tsetse endosymbiont transmission routes, and
ii- development of symbiont-based expression system.

6-Identify trypanosome inhibitory products:
produced anti-trypanosome nanobodies.

7-Incorporate parasite resistance traits into SIT lines:
could not be achieved in the time frame of this CRP (see point 5, because 7 depends on the achievement of 5).

8-Cytoplasmic incompatibility-mediated gene drive system:
i- discovered the presence of chromosomal insertions of Wolbachia symbionts in many tsetse species,
ii- discovered low titer Wolbachia infections in natural populations and colonies,
iii- determined tsetse Wolbachia genome sequences,
iv- discovered polyandry in natural tsetse populations.

9-Harness cytoplasmic incompatibility for SIT application:
i. discovered the functional role of Wolbachia in inducing high CI,
ii- A mathematical model was developed to use CI for paratransgenic application to derive desirable phenotypes.

10-Disseminate discoveries to endemic countries and interested parties and relevant databases:
i- we have built capacity in Tsetse & Trypanosome Research in participating DECs in Africa. This includes:
- Training of 6 PhD students and 8 research fellows from DECs in collaborating laboratories,
- Training of DEC researchers in collaborating laboratories through short-term visits,
- Presentations of research findings by DEC scientists in international meetings,
- Ability to recruit independent research funds to DEC scientists in collaboration with participating scientists and laboratories,
- Promote development of genomics knowledge, including genome sequencing and functional studies in multiple tsetse species through participating in International Glossina Genome Initiative.

11-Publish results in scientific journals:
See research publication list.