The transmission of mixed Trypanosoma brucei brucei/T. congolense infections by tsetse (Glossina morsitans morsitans)

Trypanosoma sp. infection in Boa constrictor snakes: morphological, hematological, clinical biochemistry, molecular, and phylogenetic characteristics

There are few reports of Trypanosoma in snakes, as well as little information about its pathogenicity in these animals. Thus, the present study aimed to characterize Trypanosoma found in Boa constrictor snakes, to verify the influence of the parasitism on hematological and clinical biochemistry parameters, and to perform a phylogenetic study of the isolates. Blood samples from sixty-one boas were analyzed for the presence of trypanosomatids and by hematological and clinical biochemistry assays. The flagellates that were found in this analysis were used for cell culture, morphometry, and molecular analysis. Later, molecular typing phylogenetic studies were performed. Nine positive animals (14.75%) were identified by microscopy analysis. The hematological results showed that parasitized animals presented significantly lower levels of packed cell volume, hemoglobin, mean corpuscular volume, and mean corpuscular hemoglobin. In the leukogram, eosinophils and heterophils counts were higher in parasitized animals. Considering the molecular analyses, the isolates presented a higher identity of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the 18S small subunit ribosomal RNA (SSU rRNA) gene fragments with Trypanosoma serpentis. The phylogenetic tree, using the GAPDH, clustered all isolates with T. serpentis and Trypanosoma cascavelli. This is the first description of T. serpentis parasitizing boas and of the clinical changes caused by trypanosomatid infection in snakes.

Development of real time PCR to study experimental mixed infections of T. congolense Savannah and T. b. brucei in Glossina morsitans morsitans

Tsetse flies are able to acquire mixed infections naturally or experimentally either simultaneously or sequentially. Traditionally, natural infection rates in tsetse flies are estimated by microscopic examination of different parts of the fly after dissection, together with the isolation of the parasite in vivo. However, until the advent of molecular techniques it was difficult to speciate trypanosomes infections and to quantify trypanosome numbers within tsetse flies. Although more expensive, qPCR allows the quantification of DNA and is less time consuming due to real time visualization and validation of the results. The current study evaluated the application of qPCR to quantify the infection load of tsetse flies with T. b. brucei and T. congolense savannah and to study the possibility of competition between the two species. The results revealed that the two qPCR reactions are of acceptable efficiency (99.1% and 95.6%, respectively), sensitivity and specificity and can be used for quantification of infection load with trypanosomes in experimentally infected Glossina morsitans morsitans. The mixed infection of laboratory Glossina species and quantification of the infection suggests the possibility that a form of competition exists between the isolates of T. b. brucei and T. congolense savannah that we used when they co-exist in the fly midgut.

Vector competence of Glossina austeni and Glossina brevipalpis for Trypanosoma congolense in KwaZulu-Natal, South Africa

Tsetse-transmitted trypanosomosis (nagana) has been the cause of stock losses in the recent past and still presents a major problem to livestock owners in certain areas of KwaZulu- Natal, South Africa. Over 10 000 cattle mortalities were reported in the 1990 nagana outbreak. Although information on the distribution and abundance of the tsetse flies Glossina brevipalpis and Glossina austeni in KwaZulu-Natal exists, data on their vector competence are lacking. This study aimed to determine the rate of natural Trypanosoma congolense infection by field-collected as well as colony-reared flies of these species. A total of 442 field-collected G. brevipalpis and 40 G. austeni flies were dissected immediately after collection to determine their infection rates, whilst 699 G. brevipalpis and 49 G. austeni flies were fed on susceptible animals in 10 and four batches, respectively, for use in xenodiagnosis experiments. Teneral colony flies were fed on infected animals and dissected 21 days post infection to confirm their infectivity testing. Glossina austeni harboured 8% immature and mature infections. In G. brevipalpis, the infection with the immature stages was lower (1%) and no mature infections were observed. Although all four batches of G. austeni transmitted T. congolense to four susceptible animals, no transmission resulted from 10 batches of G. brevipalpis fed on susceptible cattle. Colony-derived G. austeni (534) and G. brevipalpis (882) were fed on four bovines infected with different T. congolense isolates. Both G. austeni and G. brevipalpis acquired trypanosome infection from the bovines, with immature infection ranges of 20% - 33% and 1% - 4%, respectively. Parasites, however, only matured in G. austeni (average = 4%). Glossina austeni plays a larger role in the epidemiology of animal trypanosomosis in KwaZulu-Natal than G. brevipalpis and therefore more focus should be aimed at the former when control measures are implemented.

Trypanosoma brucei s.l.: Microsatellite markers revealed high level of multiple genotypes in the mid-guts of wild tsetse flies of the Fontem sleeping sickness focus of Cameroon

To identify Trypanosoma brucei genotypes which are potentially transmitted in a sleeping sickness focus, microsatellite markers were used to characterize T. brucei found in the mid-guts of wild tsetse flies of the Fontem sleeping sickness focus in Cameroon. For this study, two entomological surveys were performed during which 2685 tsetse flies were collected and 1596 (59.2%) were dissected. Microscopic examination revealed 1.19% (19/1596) mid-gut infections with trypanosomes; the PCR method identified 4.7% (75/1596) infections with T. brucei in the mid-guts. Of these 75 trypanosomes identified in the mid-guts, Trypanosoma brucei gambiense represented 0.81% (13/1596) of them, confirming the circulation of human infective parasite in the Fontem focus. Genetic characterization of the 75 T. brucei samples using five microsatellite markers revealed not only multiple T. brucei genotypes (47%), but also single genotypes (53%) in the mid-guts of the wild tsetse flies. These results show that there is a wide range of trypanosome genotypes circulating in the mid-guts of wild tsetse flies from the Fontem sleeping sickness focus. They open new avenues to undertake investigations on the maturation of multiple infections observed in the tsetse fly mid-guts. Such investigations may allow to understand how the multiple infections evolve from the tsetse flies mid-guts to the salivary glands and also to understand the consequence of these evolutions on the dynamic (which genotype is transmitted to mammals) of trypanosomes transmission.

Prevalence and source of trypanosome infections in field-captured vector flies (Glossina pallidipes) in southeastern Zambia

The prevalence of trypanosome infections in tsetse flies, Glossina pallidipes, collected from Chiawa and Chakwenga in Zambia with endemic trypanosomosis was assessed by polymerase chain reaction (PCR). Out of the 550 G. pallidipes, 58 (10.5%) flies were found to harbor trypanosome DNA. Infection rates of tsetse with Trypanosoma vivax universal, Trypanosoma congolense savannah, T. congolense forest and T. congolense kilifi were 4.2% (23/550), 4.7% (26/550), 1.1% (6/550) and 1.6% (9/550), respectively. To determine the mammalian hosts of T. congolense and T. vivax infections from the tsetse flies, mammalian mitochondrion DNA of blood meal in these flies were analyzed by PCR and subsequent gene sequence analysis of the amplicons. Sequence analysis showed the presence of cytochrome b gene (cyt b) of 7 different mammalian species such as human, elephant, buffalo, goat, warthog, greater kudu and cattle. Goats which were main livestock in these areas were further examined to know the extent of its contribution in spreading the infection. We examined the prevalence of trypanosome infections in the domestic goat population in 6 settlements in Chiawa alone. Of the 86 goats sampled, 4 (4.6%), 5 (5.8%), 4 (4.6%) and 4 (4.6%) were positive for T. vivax universal, T. congolense savannah, forest and kilifi, respectively. These findings showed that the host-source of trypanosome infections in vector fly give a vital information about spread of infection. The result of this study will certainly contribute in elucidating more the epidemiology of trypanosomosis.

Dynamics of infection and competition between two strains of Trypanosoma brucei brucei in the tsetse fly observed using fluorescent markers

Background

Genetic exchange occurs between Trypanosoma brucei strains during the complex developmental cycle in the tsetse vector, probably within the salivary glands. Successful mating will depend on the dynamics of co-infection with multiple strains, particularly if intraspecific competition occurs. We have previously used T. brucei expressing green fluorescent protein to study parasite development in the vector, enabling even one trypanosome to be visualized. Here we have used two different trypanosome strains transfected with either green or red fluorescent proteins to study the dynamics of co-infection directly in the tsetse fly.

Results

The majority of infected flies had both trypanosome strains present in the midgut, but the relative proportion of red and green trypanosome strains varied considerably between flies and between different sections of the midgut in individual flies. Colonization of the paired salivary glands revealed greater variability than for midguts, as each gland could be infected with red and/or green trypanosome strains in variable proportions. Salivary glands with a mixed infection appeared to have a higher density of trypanosomes than glands containing a single strain. Comparison of the numbers of red and green trypanosomes in the proventriculus, salivary exudate and glands from individual flies showed no correlation between the composition of the trypanosome population of the proventriculus and foregut and that of the salivary glands. For each compartment examined (midgut, foregut, salivary glands), there was a significantly higher proportion of mixed infections than expected, assuming the null hypothesis that the development of each trypanosome strain is independent.

Conclusion

Both the trypanosome strains used were fully capable of infecting tsetse, but the probabilities of infection with each strain were not independent, there being a significantly higher proportion of mixed infections than expected in each of three compartments examined: midgut, proventriculus and salivary glands. Hence there was no evidence of competition between trypanosome strains, but instead co-infection was frequent. Infection rates in co-infected flies were no different to those found routinely in flies infected with a single strain, ruling out the possibility that one strain enhanced infection with the other. We infer that each fly is either permissive or non-permissive of trypanosome infection with at least 3 sequential checkpoints imposed by the midgut, proventriculus and salivary glands. Salivary glands containing both trypanosome strains appeared to contain more trypanosomes than singly-infected glands, suggesting that lack of competition enhances the likelihood of genetic exchange.

Ability of trypanosome-infected tsetse flies (Diptera: Glossinidae) to acquire an infection with a second trypanosome species

The epidemiology of human and animal trypanosomiasis is determined to a large extent by the number of infected tsetse flies in a specific area. In the field, a substantial proportion of infected flies carry mixed trypanosome infections. The way in which these tsetse flies acquire a mixed infection is not fully understood. In particular, the susceptibility of tsetse flies to sequential infection with trypanosomes is not well understood. Accordingly, laboratory studies were made of the effects of age and prior infection on the probability of Glossina morsitans morsitans (Westwood) developing an infection of Trypanosoma congolense and Trypanosoma brucei brucei after feeding on infected mice. Results of these experiments clearly showed that 20-30-d-old G. m. morsitans can still pick up and develop a mature infection in the mouthparts/hypopharynx for T. congolense or in the salivary glands for T. b. brucei. However, their ability to acquire infection was significantly lower compared with teneral flies. Furthermore, 20-30-d-old flies that already carry a mature T. congolense or T. b. brucei infection remained at least as susceptible to a secondary trypanosome infection compared with noninfected flies of the same age. The immunological and epidemiological repercussions of those findings are discussed.

Transmissibility of Trypanosoma brucei during its development in cattle

Recent outbreaks of Trypanosoma brucei rhodesiense sleeping sickness in Soroti District of eastern Uganda have demonstrated the important role cattle can play as reservoirs of this parasite. To clarify the epidemiological importance of the cattle reservoir, experiments were conducted to determine the ease with which T. brucei is transmitted during the course of its development in Friesian cattle. The development of T. brucei in cattle is characterized by an acute phase with high levels of parasitaemia and a decline in PCV. The acute phase is followed by a chronic phase during which the PCV remains low but stable and the parasitaemia is low. Parasites are often difficult to detect using parasitological diagnostic tools during this chronic phase. Challenge of chronically infected cattle with T. congolense results in a sudden increase in the T. brucei parasitaemia. Despite significant differences in parasitaemia, the proportion of tsetse flies that developed metacyclic infections after a first bloodmeal on the infected cattle did not differ significantly between the acute and chronic phases or the phase of mixed T. b. brucei/T. congolense infection. This suggests that, throughout the observation period, the parasitaemia was above the threshold above which infection rates of tsetse are independent of the parasitaemia. The repercussions of the research findings for the understanding of the epidemiology, spread and the control of T. b. rhodesiense sleeping sickness are discussed.