Modeling Chagas disease in Chile: From vector to congenital transmission

Knowledge Production on Congenital Chagas Disease across Time, Borders and Disciplines: A Comprehensive Scoping Review

Congenital transmission is a key route of Trypanosoma cruzi infection in Latin America and globally, contributing significantly to the burden of Chagas disease. The interruption of transmission from mother to child has recently become a focus issue. However, the research landscape on congenital Chagas disease remains largely unexplored. The purpose of this scoping review is to assess the production of knowledge on congenital Chagas disease (CCD), aiming to identify research trends and potential gaps. Our initial hypothesis was that the CCD literature overly represents the medical sciences and that there is a need for socio-cultural research on the subject. We conducted a systematic search of publications focusing on congenital Chagas disease in six languages (English, Spanish, Portuguese, French, German and Italian). This comprehensive literature search identified 876 studies that met the inclusion criteria, out of a total of 8893 sources. The relevant literature was analyzed by language, year of publication, discipline, source type and research location. The main outcome of this study has been to prove our hypothesis that there is a scarcity of knowledge produced within the non-biomedical sciences on CCD. This underscores the need for further exploration into the social and structural issues surrounding this disease. Visually clear data concerning congenital Chagas disease produced by this study can contribute to hone in future research efforts and support funding applications. Additionally, this article provides a reference list that other researchers can consult for their own studies.

A description of the epidemiological dynamics of Chagas disease via mathematical modeling

Chagas disease is caused by the protozoan Trypanosoma cruzi, which parasitizes many mammals, including humans. Its vectors are blood-feeding hematophagous triatomine insects of different species, which vary according to the geographical area. One of the 17 neglected diseases targeted by the World Health Organization, Chagas disease is endemic to the Americas, but has spread to other countries due to human migratory movements. In this study, we describe the epidemiological dynamics of Chagas disease in an endemic area, considering the main transmission mechanisms and the demographic effects of birth, mortality, and human migration in this phenomenon. We apply mathematical models as a methodological approach to simulate the interactions between reservoirs, vectors, and humans using a system of ordinary differential equations. The results show that the Chagas disease control measures currently in place cannot be relaxed without endangering the progress achieved to date.

Trypanosoma cruzi infection in the wild Chagas disease vector, Mepraia spinolai: Parasitic load, discrete typing units, and blood meal sources

BACKGROUND

Mepraia spinolai, a wild vector of Trypanosoma cruzi in Chile, is an abundant triatomine species that is frequently infected by the parasite that causes Chagas disease. The aim of this study was to determine if the parasitic load of T. cruzi in M. spinolai is related to its blood meal source and the infecting DTUs of T. cruzi.

METHODS

The vector was captured in rural areas. In the laboratory, DNA was extracted from its abdomen and T. cruzi was quantified using qPCR. Real time PCR assays for four T. cruzi DTUs were performed. Blood meal sources were identified by real-time PCR amplification of vertebrate cytochrome b gene sequences coupled with high resolution melting (HRM).

RESULTS

Trypanosoma cruzi was detected in 735 M. spinolai; in 484 we identified one blood meal source, corresponding to human, sylvatic, and domestic species. From these, in 224 we were able to discriminate the infecting DTU. When comparing the parasitic loads between the unique blood meal sources, no significant differences were found, but infections with more than one DTU showed higher parasitic loads than single infections. DTU TcI was detected in a high proportion of the samples.

CONCLUSIONS

Higher parasitic loads are related to a greater number of T. cruzi DTUs infecting M. spinolai, and this triatomine seems to have a wide span of vertebrate species in its diet.

Over-dispersed Trypanosoma cruzi parasite load in sylvatic and domestic mammals and humans from northeastern Argentina

BACKGROUND

The distribution of parasite load across hosts may modify the transmission dynamics of infectious diseases. Chagas disease is caused by a multi-host protozoan, Trypanosoma cruzi, but the association between host parasitemia and infectiousness to the vector has not been studied in sylvatic mammalian hosts. We quantified T. cruzi parasite load in sylvatic mammals, modeled the association of the parasite load with infectiousness to the vector and compared these results with previous ones for local domestic hosts.

METHODS

The bloodstream parasite load in each of 28 naturally infected sylvatic mammals from six species captured in northern Argentina was assessed by quantitative PCR, and its association with infectiousness to the triatomine Triatoma infestans was evaluated, as determined by natural or artificial xenodiagnosis. These results were compared with our previous results for 88 humans, 70 dogs and 13 cats, and the degree of parasite over-dispersion was quantified and non-linear models fitted to data on host infectiousness and bloodstream parasite load.

RESULTS

The parasite loads of Didelphis albiventris (white-eared opossum) and Dasypus novemcinctus (nine-banded armadillo) were directly and significantly associated with infectiousness of the host and were up to 190-fold higher than those in domestic hosts. Parasite load was aggregated across host species, as measured by the negative binomial parameter, k, and found to be substantially higher in white-eared opossums, cats, dogs and nine-banded armadillos (range: k = 0.3-0.5) than in humans (k = 5.1). The distribution of bloodstream parasite load closely followed the "80-20 rule" in every host species examined. However, the 20% of human hosts, domestic mammals or sylvatic mammals exhibiting the highest parasite load accounted for 49, 25 and 33% of the infected triatomines, respectively.

CONCLUSIONS

Our results support the use of bloodstream parasite load as a proxy of reservoir host competence and individual transmissibility. The over-dispersed distribution of T. cruzi bloodstream load implies the existence of a fraction of highly infectious hosts that could be targeted to improve vector-borne transmission control efforts toward interruption transmission. Combined strategies that decrease the parasitemia and/or host-vector contact with these hosts would disproportionally contribute to T. cruzi transmission control.

SIR model of the pandemic trend of COVID-19 in Peru

The SARS-CoV-2 virus from Europe has reached Peru on March 5 and since March 16 a state of national emergency has been declared, leading to the confinement of the entire population. The objective of this study is to characterize the epidemic evolution of coronavirus disease (COVID-19) applying the SIR model (Susceptible-Infectious-recovered or deceased) during a period of 200 days. The time series data of COVID-19 from March 06 to May 14, 2020 of the Peruvian Ministry of Health was used, presenting estimated cases by varying the basic reproduction number R0. According to the SIR model, the peak of those infected occurs shortly after May 30 from the beginning of the epidemic (day 86) where the total number of infected cases decreases to R0 = 1.5. The results suggest that Peru's current stringent measures can effectively prevent the spread of COVID-19 and should be maintained even with efficient results.

SIR model of the pandemic trend of COVID-19 in Peru

The SARS-CoV-2 virus from Europe has reached Peru on March 5 and since March 16 a state of national emergency has been declared, leading to the confinement of the entire population. The objective of this study is to characterize the epidemic evolution of coronavirus disease (COVID-19) applying the SIR model (Susceptible-Infectious-recovered or deceased) during a period of 200 days. The time series data of COVID-19 from March 06 to May 14, 2020 of the Peruvian Ministry of Health was used, presenting estimated cases by varying the basic reproduction number R0. According to the SIR model, the peak of those infected occurs shortly after May 30 from the beginning of the epidemic (day 86) where the total number of infected cases decreases to R0 = 1.5. The results suggest that Peru's current stringent measures can effectively prevent the spread of COVID-19 and should be maintained even with efficient results.

Survivorship of wild caught Mepraia spinolai nymphs: The effect of seasonality and Trypanosoma cruzi infection after feeding and fasting in the laboratory

Chagas disease is caused by Trypanosoma cruzi. Vector survival is an important variable affecting vectorial capacity to determine parasite transmission risk. The aims of this study are to evaluate vector survival under fasting/starvation conditions of wild-caught Mepraia spinolai after feeding and fasting, the pathogenicity of T. cruzi infection, the parasite burden and seasonal variation in parasite discrete typing units (DTU). The survivorship of M. spinolai nymphs after two continuous artificial feedings was evaluated, assessing their infection with microscopic observation of fecal samples and PCR. Later, insects were fasted/starved until death. We performed qPCR analyses of parasite load in the fecal samples and dead specimens. T. cruzi genotyping was performed using conventional PCR amplicons and hybridization tests. Infection rate was higher in M. spinolai nymphs in summer and spring than in fall. Parasite burden varied from 3 to 250,000 parasites/drop. Survival rate for starved nymph stage II was lower in insects collected in the spring compared to summer and fall. TcII was the most frequent DTU. Mainly metacyclic trypomastigotes were excreted. We conclude that M. spinolai infection rate in nymphs varies among seasons, suggesting higher transmission risk in warmer seasons. However, nymphs stage II collected in spring are more sensitive to starvation compared to other seasons. TcII in single or mixed infection does not seem relevant to determine vector pathogenicity. These results of vector survivorship after fasting/starvation are important to determine the competence of M. spinolai as a vector of T. cruzi, since they excrete metacyclic trypomastigotes and the parasitism with T. cruzi seems to be poorly pathogenic to the vector under a severe fasting/starvation condition.

The effect of temperature increase on the development of Rhodnius prolixus and the course of Trypanosoma cruzi metacyclogenesis

The increase in the global land temperature, expected under predictions of climate change, can directly affect the transmission of some infectious diseases, including Chagas disease, an anthropozoonosis caused by Trypanosoma cruzi and transmitted by arthropod vectors of the subfamily Triatominae. This work seeks to study the effects of temperature on the development of the life cycle, fertility and fecundity of the insect vector Rhodnius prolixus and on the metacyclogenesis of T. cruzi. All of the variables were subjected to 3 temperatures: 26°C, 28°C and 30°C. Hatching time was evaluated, along with time to fifth instar, time to adult, fecundity studied using the e-value, and egg viability during the first 3 reproductive cycles. In addition, the amounts of metacyclic trypomastigotes of the TcI and TcII DTUs in R. prolixus were evaluated from days 2 to 20 at two-day intervals and from weeks 6 to 8 post-infection. Decreases were observed in time to hatching (15–10 days on average) and in time to fifth instar (70–60 days on average) and transition to adult (100–85 days on average). No significant differences in egg viability were observed in any of the reproductive cycles evaluated, but an increase in fecundity was observed at 30°C during the third reproductive cycle. At 30°C, there was also an increase in the number of infective forms and a decrease in the time at which metacyclic trypomastigotes were detected in the rectal ampulla of the insects for both TcI and TcII. According to these results, the expected temperature increase under climate change would cause an increase in the number of insects and a greater probability of infection of the parasite, which affects the transmission of Chagas disease.

Chagas disease is an anthropozoonosis caused by the flagellated protozoan Trypanosoma cruzi and mainly transmitted through the infected faeces of insects of the subfamily Triatominae. Because these insects are sensitive to climatic conditions, it is expected that disease transmission may be affected by the increase in global land temperature, predicted under climate change. Therefore, we wanted to evaluate the effect of temperature increase on the development, viability of eggs and fertility of R. prolixus, the most important vector insect in Colombia, and on the development of the parasite within this insect. We observed a decrease in the development time of R. prolixus and an increase in the number of infectious forms of T. cruzi in the insect as the temperature increased. These results suggest that if the temperature increases as expected, there may be an increase in the number of insects that can transmit the disease, as well as an increase in the likelihood of infection due to the increase in the number of infectious forms. Our data contributes to the understanding of the possible effects of the expected temperature increase under climate change on Chagas disease transmission and can be used to make predictive models that can more accurately predict the future of Chagas disease.

Who benefits from cellular immune response during the Chagas disease?

We extend our previous model for the dynamical interaction between a mammal's immune response and the Trypanosoma cruzi parasite during the acute phase of Chagas disease. The model here considers both humoral and cellular responses and the different stages of T. cruzi (intracellular and extracellular phases) inside the mammal host. We analyze the dynamical time evolution of the populations obtaining phase diagrams of the model results. The steady-state solution of the system yields two outcomes associated to Healing and Chronic stationary cases, the death case obtained when just the humoral immune response alone was considered is not being present. This result implies that, surprisingly, although the immune cellular response is obviously beneficial for the host, it is also evolutionary advantageous for the parasite, as it helps to preserve the host alive and, after transmission to a healthy host, perpetuate the disease. Of course, if the cell damage by the parasite's intracellular stage is high, it may cause the host death. This possibility is accounted in the model by introducing a death criterion related to cell destruction. We present a new phase diagram, that restores the host death case and generates a phase diagram similar to the one arising from the original model.

Assessing the risk zones of Chagas' disease in Chile, in a world marked by global climatic change

BACKGROUND

Vector transmission of Trypanosoma cruzi appears to be interrupted in Chile; however, data show increasing incidence of Chagas' disease, raising concerns that there may be a reemerging problem.

OBJECTIVE

To estimate the actual risk in a changing world it is necessary to consider the historical vector distribution and correlate this distribution with the presence of cases and climate change.

METHODS

Potential distribution models of Triatoma infestans and Chagas disease were performed using Maxent, a machine-learning method.

FINDINGS

Climate change appears to play a major role in the reemergence of Chagas' disease and T. infestans in Chile. The distribution of both T. infestans and Chagas' disease correlated with maximum temperature, and the precipitation during the driest month. The overlap of Chagas' disease and T. infestans distribution areas was high. The distribution of T. infestans, under two global change scenarios, showed a minimal reduction tendency in suitable areas.

MAIN CONCLUSION

The impact of temperature and precipitation on the distribution of T. infestans, as shown by the models, indicates the need for aggressive control efforts; the current control measures, including T. infestans control campaigns, should be maintained with the same intensity as they have at present, avoiding sylvatic foci, intrusions, and recolonisation of human dwellings.