Colonization of Rhodnius prolixus gut by Trypanosoma cruzi involves an extensive parasite killing.

Trypanosoma cruzi, the etiological agent of Chagas disease, is ingested by triatomines during their bloodmeal on an infected mammal. Aiming to investigate the development and differentiation of T. cruzi inside the intestinal tract of Rhodnius prolixus at the beginning of infection we fed insects with cultured epimastigotes and blood trypomastigotes from infected mice to determine the amount of recovered parasites after ingestion. Approximately 20% of the ingested parasites was found in the insect anterior midgut (AM) 3 h after feeding. Interestingly, a significant reduction (80%) in the numbers of trypomastigotes was observed after 24 h of infection suggesting that parasites were killed in the AM. Moreover, few parasites were found in that intestinal portion after 96 h of infection. The evaluation of the numbers of parasites in the posterior midgut (PM) at the same periods showed a reduced parasite load, indicating that parasites were not moving from the AM. Additionally, incubation of blood trypomastigotes with extracts from R. prolixus AMs revealed that components of this tissue could induce significant death of T. cruzi. Finally, we observed that differentiation from trypomastigotes to epimastigotes is not completed in the AM; instead we suggest that trypomastigotes change to intermediary forms before their migration to the PM, where differentiation to epimastigotes takes place. The present work clarifies controversial points concerning T. cruzi development in insect vector, showing that parasite suffers a drastic decrease in population size before epimastigonesis accomplishment in PM.

Seroprevalence, Prevalence, and Genomic Surveillance: Monitoring the Initial Phases of the SARS-CoV-2 Pandemic in Betim, Brazil.

The COVID-19 pandemic has created an unprecedented need for epidemiological monitoring using diverse strategies. We conducted a project combining prevalence, seroprevalence, and genomic surveillance approaches to describe the initial pandemic stages in Betim City, Brazil. We collected 3239 subjects in a population-based age-, sex- and neighborhood-stratified, household, prospective; cross-sectional study divided into three surveys 21 days apart sampling the same geographical area. In the first survey, overall prevalence (participants positive in serological or molecular tests) reached 0.46% (90% CI 0.12-0.80%), followed by 2.69% (90% CI 1.88-3.49%) in the second survey and 6.67% (90% CI 5.42-7.92%) in the third. The underreporting reached 11, 19.6, and 20.4 times in each survey. We observed increased odds to test positive in females compared to males (OR 1.88 95% CI 1.25-2.82), while the single best predictor for positivity was ageusia/anosmia (OR 8.12, 95% CI 4.72-13.98). Thirty-five SARS-CoV-2 genomes were sequenced, of which 18 were classified as lineage B.1.1.28, while 17 were B.1.1.33. Multiple independent viral introductions were observed. Integration of multiple epidemiological strategies was able to adequately describe COVID-19 dispersion in the city. Presented results have helped local government authorities to guide pandemic management.

New features on the survival of human-infective Trypanosoma rangeli in a murine model: Parasite accumulation is observed in lymphoid organs.

Trypanosoma rangeli is a non-pathogenic protozoan parasite that infects mammals, including humans, in Chagas disease-endemic areas of South and Central America. The parasite is transmitted to a mammalian host when an infected triatomine injects metacyclic trypomastigotes into the host's skin during a bloodmeal. Infected mammals behave as parasite reservoirs for several months and despite intensive research, some major aspects of T. rangeli-vertebrate interactions are still poorly understood. In particular, many questions still remain unanswered, e.g. parasite survival and development inside vertebrates, as no parasite multiplication sites have yet been identified. The present study used an insect bite transmission strategy to investigate whether the vector inoculation spot in the skin behave as a parasite-replication site. Histological data from the skin identified extracellular parasites in the dermis and hypodermis of infected mice in the first 24 hours post-infection, as well as the presence of inflammatory infiltrates in a period of up to 7 days. However, qPCR analyses demonstrated that T. rangeli is eliminated from the skin after 7 days of infection despite being still consistently found on circulating blood and secondary lymphoid tissues for up to 30 days post-infection. Interestingly, significant numbers of parasites were found in the spleen and mesenteric lymph nodes of infected mice during different periods of infection and steady basal numbers of flagellates are maintained in the host's bloodstream, which might behave as a transmission source to insect vectors. The presence of parasites in the spleen was confirmed by fluorescent photomicrography of free and cell-associated T. rangeli forms. Altogether our results suggest that this organ could possibly behave as a T. rangeli maintenance hotspot in vertebrates.

Revisiting Trypanosoma rangeli Transmission Involving Susceptible and Non-Susceptible Hosts.

Trypanosoma rangeli infects several triatomine and mammal species in South America. Its transmission is known to occur when a healthy insect feeds on an infected mammal or when an infected insect bites a healthy mammal. In the present study we evaluated the classic way of T. rangeli transmission started by the bite of a single infected triatomine, as well as alternative ways of circulation of this parasite among invertebrate hosts. The number of metacyclic trypomastigotes eliminated from salivary glands during a blood meal was quantified for unfed and recently fed nymphs. The quantification showed that ~50,000 parasites can be liberated during a single blood meal. The transmission of T. rangeli from mice to R. prolixus was evaluated using infections started through the bite of a single infected nymph. The mice that served as the blood source for single infected nymphs showed a high percentage of infection and efficiently transmitted the infection to new insects. Parasites were recovered by xenodiagnosis in insects fed on mice with infections that lasted approximately four months. Hemolymphagy and co-feeding were tested to evaluate insect-insect T. rangeli transmission. T. rangeli was not transmitted during hemolymphagy. However, insects that had co-fed on mice with infected conspecifics exhibited infection rates of approximately 80%. Surprisingly, 16% of the recipient nymphs became infected when pigeons were used as hosts. Our results show that T. rangeli is efficiently transmitted between the evaluated hosts. Not only are the insect-mouse-insect transmission rates high, but parasites can also be transmitted between insects while co-feeding on a living host. We show for the first time that birds can be part of the T. rangeli transmission cycle as we proved that insect-insect transmission is feasible during a co-feeding on these hosts.

Trypanosomes Modify the Behavior of Their Insect Hosts: Effects on Locomotion and on the Expression of a Related Gene.

BACKGROUND: As a result of evolution, the biology of triatomines must have been significantly adapted to accommodate trypanosome infection in a complex network of vector-vertebrate-parasite interactions. Arthropod-borne parasites have probably developed mechanisms, largely still unknown, to exploit the vector-vertebrate host interactions to ensure their transmission to suitable hosts. Triatomines exhibit a strong negative phototaxis and nocturnal activity, believed to be important for insect survival against its predators. METHODOLOGY/PRINCIPAL FINDINGS: In this study we quantified phototaxis and locomotion in starved fifth instar nymphs of Rhodnius prolixus infected with Trypanosoma cruzi or Trypanosoma rangeli. T. cruzi infection did not alter insect phototaxis, but induced an overall 20% decrease in the number of bug locomotory events. Furthermore, the significant differences induced by this parasite were concentrated at the beginning of the scotophase. Conversely, T. rangeli modified both behaviors, as it significantly decreased bug negative phototaxis, while it induced a 23% increase in the number of locomotory events in infected bugs. In this case, the significant effects were observed during the photophase. We also investigated the expression of Rpfor, the triatomine ortholog of the foraging gene known to modulate locomotion in other insects, and found a 4.8 fold increase for T. rangeli infected insects. CONCLUSIONS/SIGNIFICANCE: We demonstrated for the first time that trypanosome infection modulates the locomotory activity of the invertebrate host. T. rangeli infection seems to be more broadly effective, as besides affecting the intensity of locomotion this parasite also diminished negative phototaxis and the expression of a behavior-associated gene in the triatomine vector.

Explorando o ciclo de transmissão do Trypanosoma rangeli: avaliação do papel das aves na circulação do parasito em triatomíneos, e dos eventos que ocorrem na fase inicial da infecção em camundongos

O Trypanosoma rangeli é um parasito que possui triatomíneos e mamíferos, incluindo o homem, como hospedeiros. Os triatomíneos adquirem a infecção ao se alimentarem em mamíferos infectados. O parasito é transmitido ao mamífero durante a picada no ato da alimentação. Até o momento, não se conhece o ciclo de desenvolvimento do T.rangeli no hospedeiro vertebrado. Primeiramente, foi avaliado se aves também poderiam participar da disseminação do parasito entre insetos. Insetos infectados (doadores) e não infectados (receptores) foram alimentados simultaneamente em pombos não infectados (co-alimentação). Os insetos receptores que co-alimentaram em pombos com insetos doadores na proporção 1:1 apresentaram uma taxa de infecção de 16%, que foi reduzida para 9% quando a proporção foi alterada para 5:1 e a distância receptores/doador aumentada. Quando os receptores se alimentaram no pombo após o término da alimentação do doador, a infecção não foi observada. A susceptibilidade de tripomastigotas metacíclicos de T.rangeli ao sistema complemento de pombos e camundongos também foi analisada. Os resultados mostraram que os tripomastigotas foram resistentes ao sistema complemento de camundongos, mas suscetíveis aos de pombos. A transmissão do protozoário através da co-alimentação de triatomíneos em pombos indica que esse comportamento permite que parasitos cheguem ao intestino de um inseto saudável antes da ação do sistema complemento. Essa é a primeira vez em que se demonstra que aves podem participar do ciclo de transmissão de T. rangeli, ao permitirem a transferência de parasitos entre insetos durante a co-alimentação. O próximo objetivo foi avaliar a fase inicial da infecção por T.rangeli em camundongos. Inicialmente, a capacidade do parasito de estabelecer a infecção no camundongo foi avaliada a partir de parasitos liberados na pele. Observou-se uma taxa de infecção de 50% para camundongos expostos a picadas de triatomíneos infectados e 100% para camundongos expostos a parasitos liberados na pele após punção. A avaliação histológica da pele de camundongos expostos ao parasito mostrou a presença de parasitos extracelulares nas primeiras 24h após a exposição. Entretanto, infiltrados inflamatórios foram encontrados até o 7º dia pós-exposição (d.p.e), sendo eosinófilos e mastócitos as células mais comumente encontradas no sítio da infecção. Utilizando-se a técnica de qPCR foi possível detectar a presença do protozoário na pele de camundongos por até 7d.p.e. A quantificação dos parasitos presentes na pele mostrou não haver diferenças significativas no número de parasitos, quando comparados os diferentes tempos de exposição. O sangue, os linfonodos mesentéricos e o baço foram também avaliados. O DNA do parasito foi detectado nas amostras de sangue em todos os períodos, com um discreto aumento no segundo dia após a infecção. Os linfonodos mesentéricos apresentaram DNA do parasito durante toda a avaliação, além de um aumento significativo no seu peso, em relação ao grupo controle. No baço, o DNA do protozoário foi detectado em amostras referentes aos dias 1, 7 e 15d.p.e. O peso do baço foi significativamente aumentado nos animais infectados. Os resultados do estudo sugerem que os linfonodos possam funcionar como locais de manutenção do T. rangeli. Estudos adicionais serão realizados para a confirmação desses resultado.