Region in which Trypanosoma vivax originated is identified
November 01, 2017
By Peter Moon | Agência FAPESP – A study conducted in Africa and led by researchers from the University of São Paulo (USP) in Brazil has found the greatest genetic diversity in Trypanosoma vivax – a pathogenic parasite for cattle, sheep and goats – in East Africa, probably the parasite’s region of origin and diversification.
The aim of the study is to map the parasite’s diversity and dispersion routes. It has been conducted for the past ten years by researchers in the Parasitology Department of the university’s Biomedical Science Institute (ICB-USP).
Led by Marta Maria Geraldes Teixeira and Erney Plessmann de Camargo, both of whom are professors at ICB-USP, the research team comprises a large number of scientists from universities in Brazil and other South American countries, as well as Africa and the United Kingdom, who are investigating the phylogeny and evolution of trypanosomes in general.
Recent findings from the research, which is supported by FAPESP, have been published in the journals Parasites & Vectors and Infection, Genetics and Evolution. The first two authors are Herakles Antonio Garcia Perez, a professor at the Central University of Caracas, Venezuela, and holder of a postdoctoral scholarship from FAPESP, and Carla Monadeli Filgueira Rodrigues, who has a postdoctoral scholarship from Brazil’s National Council for Scientific & Technological Development (CNPq).
The best-known species of trypanosome are T. brucei, responsible for sleeping sickness (African trypanosomiasis), which is transmitted by the tsetse fly in Africa, and T. cruzi, which causes Chagas disease in Latin America and is transmitted by the insect Triatoma infestans.
According to Camargo, trypanosomes that are pathogenic for ungulates are transmitted only by tsetse flies (Glossina) and hence confined to Africa. “However, T. vivax may also be transmitted mechanically by other hematophagous flies in arid regions of Africa such as the Sahel, a vast semi-arid region south of the Sahara Desert, and of Central and South America,” he said.
According to Teixeira, the genetic variability found in East Africa suggests that this region is where T. vivax originated and diversified.
“When we began comparing Brazilian and African isolates of T. vivax, we were able to obtain only a single sample from East Africa. This isolate was very different from our own and from the reference strain of T. vivax from Nigeria, in West Africa, the only one that had been studied in depth until then,” he said.
The Brazilian group participated in sample collection in Africa under the aegis of CNPq’s “ProAfrica” project, which involved researchers from Brazil and African countries.
In the first study, conducted in Mozambique, the researchers found a new genotype when they sequenced DNA from antelope blood samples. This discovery was followed by new genotypes of T. vivax identified in Tanzania with the collaboration of UK scientists.
“Our initial findings indicated substantial diversity of T. vivax in East Africa,” Teixeira said. “We decided to study the matter in more depth. To make things more complicated, the new genotypes were being found in wild ungulates – buffalo, antelope, zebra and giraffe, which don’t develop the disease – and tsetse flies in protected areas. The study was only possible because we were given permission to work in Gorongosa National Park and Niassa Reserve in Mozambique.”
Molecular analysis of trypanosomes from a large number of tsetse flies and ungulate blood revealed two groups of T. vivax genotypes. One had few genotypes, and these were genetically similar to the genotypes found in West Africa and South America. The other comprised over 11 highly divergent genotypes, suggesting the existence of other species hitherto exclusive to East Africa.
The evidence of far greater diversity of T. vivax in East Africa suggests this is the region in which the parasite originated and diversified millions of years ago. “However, it could also point to the existence of recombinations in the tsetse of different genotypes that circulate among wild animals – a phenomenon not yet proven in T. vivax. This hypothesis needs to be tested,” Camargo said.
In contrast with East Africa, studies of T. vivax in South America conducted by Garcia Perez and Filgueira Rodrigues, among others, show significant genetic homogeneity among populations in endemic areas and isolates of sick or asymptomatic animals. The inference is that the parasites of West Africa and South America are highly similar, albeit not identical.
“Recent studies have revealed significant differences in the genomes of isolates from South America and Africa,” Teixeira said.
The results of genetic polymorphism analysis using microsatellite markers suggest the parasite may have been introduced to the Americas from West Africa, probably at several different times in the past 500 years. Findings from this analysis were published in 2014 in Parasites & Vectors.
“Animals infected with T. vivax may have been brought in the caravels of Spanish and French voyagers from their West African colonies,” Camargo said.
The first cases of the disease were described only as early as 1830 in French Guiana, the Caribbean, Venezuela and North Brazil.
“Historians think the T. vivax found in Brazil came from Senegal via French Guiana,” Camargo said. “It’s possible, as our semi-arid regions are very similar to Senegal and the Sahel in general. The donkey herd in these regions is enormous, and these animals are highly trypanotolerant, so they’re asymptomatic and serve as reservoirs for T. vivax.”
According to Camargo, this was what stimulated Rodrigues to begin studying the pathology of outbreaks of T. vivax in Brazil’s semi-arid region. She decided to look for T. vivax in abandoned donkeys wandering the roads of Rio Grande do Norte, the state in which she was born. The results of their research were published in 2015 in Parasites & Vectors.
“This also happens in Ethiopia, where T. vivax is highly prevalent,” Camargo said. “When we analyzed the genetic diversity of trypanosomes, we found significant differences in tsetse flies captured there recently. It seems that T. vivax followed historical routes of human migrations with their herds, originating in East Africa, migrating to West Africa and from there being brought to the New World. It’s a long voyage, one of many that started in the Rift Valley [a complex of tectonic faults created some 35 million years ago, when the African and Arabian plates separated]. We have yet to identify the exact routes of the voyage.”
Outbreaks of high mortality in cattle in Brazil
The Amazon and Pantanal regions of Brazil, as well as the Llanos of Venezuela, are endemic for T. vivax. Asymptomatic cattle and water buffaloes from there are introduced into areas without the parasite, triggering outbreaks of acute disease with large numbers of parasites in the blood that cause severe hematological and neurological disturbances, as observed by the researchers from ICB-USP.
“Our group observed several outbreaks of T. vivax. When we began our research, a major difficulty was diagnosing trypanosome infection. We developed a method using PCR [polymerase chain reaction], which has been used in South America and Africa, and we standardized new markers and molecular methods to analyze diversity and phylogenetic relationships,” Teixeira said.
“The outbreak of acute infection with high mortality was described in 2007 in dairy cattle in Paraíba, Northeast Brazil, with the participation of our group. Since then, outbreaks of infection by T. vivax have been described in Ceará, Pernambuco, Minas Gerais, Tocantins, Rio Grande do Sul, Goiás and São Paulo.”
Mortality can be high if animals are not treated rapidly. The animals that develop chronic disease suffer from reproductive alterations, abortions, and reduced milk production.
“The current situation in Brazil is serious. The number of sick animals is underestimated because farmers don’t notify the authorities,” Teixeira said. “However, as noted by Herakles Garcia, the situation is far worse in Venezuela, where buffaloes, which are supertrypanotolerant, are dying from infection by T. vivax.”
According to Teixeira, the group of researchers went to Africa to investigate the history of T. vivax. “There, we found out much more, including several discoveries of importance to studies of the evolution of trypanosomes in crocodiles, lizards, toads, birds and bats. We described African bat trypanosomes phylogenetically related to T. cruzi. But that’s another story, much older and more complicated, because bats fly.”
The article “Remarkable richness of trypanosomes in tsetse flies (Glossina morsitans morsitans and Glossina pallidipes) from the Gorongosa National Park and Niassa National Reserve of Mozambique revealed by fluorescent fragment length barcoding (FFLB)” by Herakles A. Garcia, Carla M. F. Rodrigues, Adriana C. Rodrigues, Dagmar L. Pereira, Carlos L. Pereira, Erney P. Camargo, P.B. Hamilton and Marta M. G. Teixeira, published in Infection, Genetics and Evolution, can be retrieved from doi.org/10.1016/j.meegid.2017.07.005.
The article “New insights from Gorongosa National Park and Niassa National Reserve of Mozambique increasing the genetic diversity of Trypanosoma vivax and Trypanosoma vivax-like in tsetse flies, wild ungulates and livestock from East Africa” (doi: https://doi.org/10.1186/s13071-017-2241-2) by Carla M.F. Rodrigues, Herakles A. Garcia, Adriana C. Rodrigues, André G. Costa-Martins, Carlos L. Pereira, Dagmar L. Pereira, Zakaria Bengaly, Luis Neves, Erney P. Camargo, Patrick B. Hamilton and Marta M.G. Teixeira is available at: parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-017-2241-2.
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