Trypanosoma Cruzi lineage-specific Serology: New Rapid Tests for Resolving Clinical and Ecological Associations

The protozoan parasite Trypanosoma cruzi, the agent of Chagas disease (American trypanosomiasis), remains a major public health concern in Latin America. The insect vectors are haematophagous triatomine bugs that, during or after their blood meal, pass the infective form of T. cruzi with feces; the parasite can then enter the host through mucosal membranes, the conjunctiva or abraded skin. Other routes of infection are congenital, oral or via blood/organ donation. The acute phase of infection lasts up to a few weeks, with nonspecific, self-resolving symptoms, although deaths can occur in this phase, particularly in children or young adults. The subsequent chronic phase of infection is life-long unless successfully treated, and asymptomatic (indeterminate) in the majority of patients. However, approximately 30% of infected individuals will develop chronic cardiac and/or gastrointestinal pathologies, with sudden death due to chagasic cardiomyopathy [1]. Chronic symptoms may manifest years or decades after the initial infection; currently, there is no prognostic indicator. A recent WHO report estimates that 5–6 million people are infected with T. cruzi [2]. Although vector-borne transmission is confined to the Americas, Chagas disease among migrants from Latin America has become of global health relevance. Trypanosoma cruzi displays remarkable intraspecies diversity, with six genetic lineages (TcI-TcVI) [3], and a proposed seventh, TcBat [4]. The possible association of different lineages of T. cruzi with distinct forms of the disease is a long-standing research interest [5]: the cardiac syndrome is found throughout the endemic area, whereas mega syndromes of the colon and esophagus have rarely been reported beyond the southern cone countries of South America. Trypanosoma cruzi is a zoonosis, with all mammals being susceptible to infection, and humans becoming a later host following the historic peopling of the Americas. The association between T. cruzi lineages, vectors and domestic, peridomestic and sylvatic animals and ecological cycles is complex [6,7]. Investigating the association between infecting lineage(s) and clinical outcome or ecological cycles has faced significant confounding challenges: the sequestration of the parasite in host tissues during the chronic phase, possibly in a lineage-dependent manner, hampers lineage identification by direct genotyping; in vitro culture of isolates may favor the selection of certain lineages. Current serological techniques identify T. cruzi specific antibodies (usually IgG), but are not designed to identify infecting lineage. The possibility therefore arose that serology based on lineage-specific T. cruzi antigens could overcome these difficulties, as it would allow the identification of an individual’s history of lineage infection without the need to genotype or isolate the parasite. In 2002, Di Noia and colleagues [8] published a pioneering report on TSSA, a mucin expressed on the mammalian bloodstream form of T. cruzi. This allowed researchers to enter a new era of lineage-specific serology for this parasite. Following the initial characterization, greater diversity of the protein core of TSSA was revealed [9]. There is a short