Comparison of the transmissibility ofTrypanosoma congolensestrains, isolated in a trypanosomiasis endemic area of eastern Zambia, byGlossina morsitans morsitans

Abstract

Transmission experiments were conducted to compare the transmissibility of genetically different Trypanosoma congolense (Savannah subgroup) strains isolated from cattle in a trypanosomiasis endemic area of eastern Zambia. A total of 17 strains were compared. Three strains were extremely virulent with a short pre-patent period, high parasitaemia and a short median survival time (between 5 and 9 days) in mice. The remainder of the strains belonged to the moderate (6 strains) or low (8 strains) virulence categories with median survival times between 10 and 30 days and >30 days, respectively. Batches of 40 teneral Glossina morsitans morsitans (Diptera: Glossinidae) were offered a single bloodmeal on mice infected with one of those strains. Flies were dissected to determine their infection status 21 days later. The proportion of flies with procyclic and metacyclic infections differed significantly between trypanosome strains and were significantly higher in flies infected with extremely virulent strains (P=0.033 and P=0.016 for the differences in the procyclic infection rate of strains with moderate and low virulence, respectively and P=0.005 and P=0.019 for the differences in the metacyclic infection rate of strains with moderate and low virulence, respectively). On the other hand, moderately virulent strains had, in general, higher procyclic and metacyclic infection rates compared to low virulent strains. But the differences were not significant (P>0.05). The outcome of those experiments shows clear differences in transmissibility of trypanosome strains associated with their virulence. This observation confirms the theory for the evolution and maintenance of virulence in a parasite population and may explain the persistence of virulent trypanosome strains in a susceptible host population.

Shifting from wild to domestic hosts: The effect on the transmission of Trypanosoma congolense to tsetse flies

“…In spite of this, both domestic and sylvatic trypanosome strains were found significantly better transmitted if they are more pathogenic to mice, even when the number of trypanosomes present in the blood meal is standardized. This observation is in agreement with the findings of Masumu et al(2006b). The parasite dose used in our study (50 trypanosomes/µl) was well above the dose we observed to cause a threshold (12.5 trypanosomes/µl), thus indicating that this difference was not due to parasite density as assumed by the simple trade-off model of Anderson and May (1982).…”

“…A linear relationship was reported between the transmissibility of the parasite and the host parasitaemia at low parasite concentrations only (10 -3 to 5 trypanosomes/µl) (Walshe et al, 2011). Moreover, for the same level of parasitaemia in mice, more pathogenic strains are more transmissible to tsetse flies (Masumu et al, 2006b). Hence the question: in a domestic environment how effective is the transmission of T. congolense to tsetse flies compared to trypanosomes cycling in a sylvatic environment if domestic strains present a lower pathogenicity and a lower proliferation capacity?…”

“…The T. congolense isolates were categorized as highly pathogenic (median survival time of infected mice < 10 days) and lowly pathogenic strains (median survival time of infected mice > 30 days) (Masumu et al, 2006b). …”

Endemic type of animal trypanosomiasis is not associated with lower genotype variability of Trypanosoma congolense isolates circulating in livestock

“…However, previous studies have shown that this species is composed of subspecies differing at genetic (Gashumba et al, 1988; Knwoles et al, 1988; Young and Godfrey, 1983) and biological (Bengaly et al, 2002; Reifenberg et al, 1997) level. Furthermore, trypanosome isolates belonging to the same subspecies and circulating in a restricted area have been found to differ in virulence (Masumu et al, 2006a), transmissibility (Masumu et al, 2006b) and antigenicity (Frame et al, 1990; Masake et al, 1987). Such differences were thought to influence the outcome of the disease in different areas.…”

Association of Pathogen Strain-Specific Gene Transcription and Transmission Efficiency Phenotype of Anaplasma marginale

“…For example, cholera pandemics are associated with a limited diversity of related, highly transmissible Vibrio cholerae strains (4). For vectorborne pathogens, efficient transmission is also dictated by infection and replication within the arthropod host (10,15,25,26). While the basic cycle of development within the arthropod vector has been identified for many important pathogens, including Anaplasma, Borrelia, Plasmodium, Rickettsia, and Trypanosoma, the critical microbial determinants of transmission efficiency in the vector remain unknown for most bacterial and protozoan pathogens.…”