Should Trypanosoma cruzi be called "cruzi" complex? A review of the parasite diversity and the potential of selecting population after in Vitro culturing and mice infection

Morpho-biological diversity of Trypanosoma cruzi has been known since Chagas' first works in 1909. Several further studies confirmed the morphological differences among the parasite strains, which were isolated from different reservoirs and vectors, as well as from human beings. In the early sixties, antigenic differences were found in the parasite strains from various sources. These differences, coupled to the observation of regional variations of the disease, led to the proposal of the term cruzi complex to designate the taxon T. cruzi. Since then this protozoan has been typed in distinct biodemes, zymodemes and lineages which were consensually grouped into T. cruzi I, T. cruzi II and into non-grouped strains. T. cruzi genotypic characterization, initially carried out by schizodeme analysis and more recently by various other techniques, has shown a great diversity of the parasite strains. In fact, T. cruzi is formed by groups of heterogeneous sub-population, which present specific characteristics, including distinct histotropism. The interaction of the different infecting clones of the cruzi complex and the human host will determine the morbidity of the disease.

Diversity of biting midges of the genus Culicoides Latreille (Diptera: Ceratopogonidae) in the area of the Yacyretá Dam Lake between Argentina and Paraguay

The Culicoides communities have been analyzed between 1993/1998 in the area influenced by the Yacyretá Dam Lake (Paraná River, Argentina-Paraguay). Adults of Culicoides were collected monthly by using CDC light traps exposed for 24 h in 9 sampling sites located at both margins of the river; 21 species were recorded. Highest values of species richness were recorded during 1993/1994, being Quiteria and Corpus the sites with the higest number of species (10 and 11, respectively). The species diversity was elevated in Quiteria, Zaimán, Candelaria, Santa Tecla, Capitán Meza and Corpus (Shannon's diversity index 1.0-1.9) while Corateí, Ituzaingó and Aguapey showed less richness and diversity. The more abundant species were C. insignis, C. venezuelensis, C. leopoldoi, C. limai, C. flinti, C. debilipalpis, C. paraensis and C. guttatus. C. insignis, potential vector of bluetongue virus (BTV) to domestic and wild rumiants in the Neotropical region, is the predominant species in the area and was the only species widely distributed. C. paraensis, a proven vector of Oropouche virus to humans, is a common and abundant species. C. pusillus and C. lahillei, potential vectors of BTV and a filarial parasite, respectively, were occasionally collected. The taxonomic structure of communities was constant during the study period. The occasional species were not characteristic to one particular site and their presence could be related to non-intrinsic conditions.

Impact of residual spraying on Rhodnius prolixus and Triatoma dimidiata in the department of Zacapa in Guatemala

As a vector control program to control Chagas disease in Guatemala, residual spraying of Rhodnius prolixus and Triatoma dimidiata was performed, and its impact was measured in the department of Zacapa. In order to identify infested villages and determine the degree of infestation, a baseline entomological survey to identify municipalities infested with vectors followed by an additional vector survey in areas known to be infested was conducted. Residual spraying using pyrethroid insecticides was performed at all the villages identified as being infested with the vectors. The residual spraying was shown to be highly effective against both vectors by the decrease in infestation indices after spraying. Analysis of the cost-effectiveness of the spraying showed that the average cost of insecticides per house is high when compared with that in Southern Cone countries.

Epidemiology of Chagas disease in Guatemala: infection rate of Triatoma dimidiata, Triatoma nitida and Rhodnius prolixus (Hemiptera, Reduviidae) with Trypanosoma cruzi and Trypanosoma rangeli (Kinetoplastida, Trypanosomatidae)

A five-year domiciliary collection in the 22 departments of Guatemala showed that out of 4,128 triatomines collected, 1,675 were Triatoma dimidiata (Latreille, 1811), 2,344 were Rhodnius prolixus Stal 1859, and only 109 were T. nitida Usinger 1939. The Chagas disease parasite, Trypanosoma cruzi, was found in all three species. Their natural infection rates were similar in the first two species (20.6%; 19.1%) and slightly lower in T. nitida(13.8%). However there was no significant difference in the infection rates in the three species (p = 0.131). T. dimidiata males have higher infection rates than females (p = 0.030), whereas for R. prolixus there is no difference in infection rates between males and females (p = 0.114). The sex ratios for all three species were significantly skewed. More males than females were found inside houses for T. dimidiata (p < 0.0001) and T. nitida (p = 0.011); a different pattern was seen for R. prolixus (p = 0.037) where more females were found. Sex ratio is proposed as an index to show the mobility of T. dimidiata in different populations. T. dimidiata is widely distributed in the country, and is also the main vector in at least ten departments, but R. prolixus with higher vectorial capacity is an important vector in at least two departments.

Comparative study of the stridulatory sulcus, buccula and rostrum of the nymphs of Triatoma guazu Lent & Wygodzinsky, 1979 and Triatoma jurbergi Carcavallo, Galvão & Lent, 1998 by scanning electron microscopy (Hemiptera, Reduviidae)

The ultrastructural morphology of the ventral region of the head (rostrum and buccula) and proesternum (stridulatory sulcus) of nymphs from the 1st to 5th instars of Triatoma guazu Lent & Wygodzinsky, 1979 and Triatoma jurbergi Carcavallo, Galvão & Lent, 1998 was described. Morphological differences between the two species and of the five nymphal stages development of each species were observed. These structures showed systematic differential characteristics of the studied species and may be used to increase their taxonomic range.

Trypanosoma (Herpetosoma) rangeli Tejera, 1920: an updated review

Trypanosoma rangeli, a parasite generally considered non-pathogenic for man, is the second species of human trypanosome to be reported from the New World. The geographical distribution of T. rangeli often overlaps with that of T. cruzi, the same vertebrate and invertebrate hosts being infected. Their differentiation thus becomes of real, practical importance, particularly as they share approximately half the antigenic determinants recognized by the humoral response. Little is known about the life cycle of T. rangeli in the vertebrate host, although thousands of human and wild animal infections have been reported. Recent studies have revealed 2 major phylogenetic lineages in T. rangeli having different characteristics, thus leading to better understanding of the epidemiology and interactions with this parasite's vertebrate hosts and triatomine vectors. Based on further genetic characterization analysis, the authors have proposed 2 alternative hypotheses and consider that T. rangeli could have had clonal evolution or have been subjected to speciation processes.

Random amplified polymorphic DNA analysis of Anopheles nuneztovari (Diptera: Culicidae) from Western and Northeastern Colombia

Random amplified polymorphic DNA (RAPD) markers were used to analyze 119 DNA samples of three Colombian Anopheles nuneztovari populations to study genetic variation and structure. Genetic diversity, estimated from heterozygosity, averaged 0.34. Genetic flow was greater between the two populations located in Western Colombia (F ST: 0.035; Nm: 6.8) but lower between these two and the northeastern population (F ST: 0.08; Nm: 2.8). According to molecular variance analysis, the genetic distance between populations was significant (phiST 0.1131, P < 0.001). The variation among individuals within populations (phiST 0.8869, P < 0.001)was also significant, suggesting a greater degree of population subdivision, not considered in this study. Both the parameters evaluated and the genetic flow suggest that Colombian An. nuneztovari populations are co-specific.

Chagas disease: current epidemiological trends after the interruption of vectorial and transfusional transmission in the Southern Cone countries

Chagas disease, named after Carlos Chagas who first described it in 1909, exists only on the American Continent. It is caused by a parasite, Trypanosoma cruzi, transmitted to humans by blood-sucking triatomine bugs and by blood transfusion. Chagas disease has two successive phases, acute and chronic. The acute phase lasts 6 to 8 weeks. After several years of starting the chronic phase, 20% to 35% of the infected individuals, depending on the geographical area will develop irreversible lesions of the autonomous nervous system in the heart, esophagus, colon and the peripheral nervous system. Data on the prevalence and distribution of Chagas disease improved in quality during the 1980's as a result of the demographically representative cross-sectional studies carried out in countries where accurate information was not available. A group of experts met in Brasília in 1979 and devised standard protocols to carry out countrywide prevalence studies on human T. cruzi infection and triatomine house infestation. Thanks to a coordinated multi-country program in the Southern Cone countries the transmission of Chagas disease by vectors and by blood transfusion has been interrupted in Uruguay in1997, in Chile in 1999, and in 8 of the 12 endemic states of Brazil in 2000 and so the incidence of new infections by T. cruzi in the whole continent has decreased by 70%. Similar control multi-country initiatives have been launched in the Andean countries and in Central America and rapid progress has been recorded to ensure the interruption of the transmission of Chagas disease by 2005 as requested by a Resolution of the World Health Assembly approved in 1998. The cost-benefit analysis of the investments of the vector control program in Brazil indicate that there are savings of US$17 in medical care and disabilities for each dollar spent on prevention, showing that the program is a health investment with good return. Since the inception in 1979 of the Steering Committee on Chagas Disease of the Special Program for Research and Training in Tropical Diseases of the World Health Organization (TDR), the objective was set to promote and finance research aimed at the development of new methods and tools to control this disease. The well known research institutions in Latin America were the key elements of a world wide network of laboratories that received - on a competitive basis - financial support for projects in line with the priorities established. It is presented the time line of the different milestones that were answering successively and logically the outstanding scientific questions identified by the Scientific Working Group in 1978 and that influenced the development and industrial production of practical solutions for diagnosis of the infection and disease control.

Estudo morfométrico do gênero Panstrongylus Berg, 1879 (Hemiptera, Reduviidae, Triatominae)

The subfamily Triatominae is actually represented by 137 species distributed among 6 tribes and 19 genera. Within this subfamily, the genus Panstrongylus, Berg 1879, is composed by 13 species widespread in sylvatic, peridomestic, and domestic habitats of Neotropical regions. These species are vectors of Chagas disease and consequently are found associated with its main hosts, such as birds and mammals. Interest in species of this genus has been increasing in the last few years. Reports of several authors indicate these Triatominae to invade and colonize houses, increasing their epidemiological significance. Morphometry was used in this study to investigate correlations among possible closely related species. We measured 224 specimens among 13 species through a set of metric variables of the head. The results indicated that the genus Panstrongylus seems to be homogeneous since 10 of the 14 species were shown to be closely related.

Redescription of Nyssomyia intermedia (Lutz & Neiva, 1912) and Nyssomyia neivai (Pinto, 1926) (Diptera: Psychodidae)

The phlebotomine sand flies Nyssomyia intermedia and Nyssomyia neivai are the probable vectors of American tegumentary leishmaniasis in the Southern and Southeastern regions of Brazil. These species form a complex, being difficult to separate between either females or males of the two members based on recognized morphological characteristics. Both N. intermedia and N. neivai are redescribed here in the search for characters that facilitate their correct identification. It was possible to differentiate females by means of spermathecal characteristics. Males could be separated with confidence by the tips of the genital filaments, which have the form of a deep spoon, the angle of the concavity being well accentuated in N. intermedia and much shallower in N. neivai.

The fossil tabanids (Diptera Tabanidae): when they began to appreciate warm blood and when they began transmit diseases?

A discussion of the known fossil tabanids (Diptera Tabanidae) is presented based on fossil evidence. This includes the origin of the hemathophagy in the Brachycera, more specifically for tabanids. Several tabanid species in the extant fauna are vectors for disease-producing organisms that affect humans and animals. Bacteria, viruses, rickettsiae, protozoa, and filarial worms can be transmitted by them, causing such diseases as anthrax, tularemia, anaplasmosis, various forms of trypanosomiasis, Q fever, and filariasis. However, if tabanids are directly responsible for all of these diseases is not consensual and the known fossil evidence is presented here.

Fossil psychodoid flies and their relation to parasitic diseases

Psychodid sand flies are blood-sucking fly vectors of several parasitic diseases. The oldest definitive record of this group is from the Lower Cretaceous amber of Lebanon (circa -135 to -125 My), but the high diversity within this group supports the idea that the psychodoids originated much earlier in history. The palaeontology demonstrates that the Lower Cretaceous representatives of the different subfamilies of Psychodidae had similar morphology and were blood-feeders, which supports Hennig's hypothesis on the ground plan structure of this family. Historical relationship between sand flies and diseases is unclear up to the present time, but this relationship could be as old as the origin of psychodoids because of the blood-feeding life mode.

Relationships of new world Phlebotomine sand flies (Diptera: Psychodidae) based on fossil evidence

The fossil record and systematics of phlebotomid sand flies, vectors of leishmaniasis and arbovirus in several regions of the world, strongly support that living genera existed long before the Oligocene (38 million years, myr). A common Phlebotominae ancestor was present in the Triassic period before the separations of continents (248 myr).

Molluscicidal effect of nicotinanilide and its intermediate compounds against a freshwater snail Lymnaea luteola, the vector of animal schistosomiasis

The molluscicidal effect of nicotinanilide was evaluated and compared with niclosamide (2',5-dichloro-4'-nitrosalicylanilide, ethanolamide salt) against different stages of the freshwater snail Lymnaea luteola i.e., eggs, immature, young mature, and adults. Calculated values of lethal concentrations (LC50 and LC90 ) showed that both nicotinanilide and niclosamide as toxic against eggs, immature, and adults. The young mature stage of the snails was comparatively more tolerant to both molluscicides than the other stages. The toxicity of the intermediate compounds of nicotinanilide against the young mature stage of the snails showed them as ineffective. The mortality pattern of the snails exposed to LC90 concentration of these molluscicides showed niclosamide to kill faster (within 8 to 9 h) than nicotinanilide (26 to 28 h). In view of the above studies it may be concluded that both molluscicides are toxic against all the stages of the L. luteola snails.

Blackflies (Diptera: Simuliidae) of Southern Guyana with keys for the identification of adults and pupae: a review

A revision is made of the previously poorly studied blackfly fauna from the south-western border of Guyana with Brazil. Notes on the biosystematics of the species found are provided, together with keys and illustrations based on their morphology. Of the 14 species recorded, eight are anthropophilic and two of these (Simulium oyapockense s.l. and S. guianense s.l.) are proven vectors of human onchocerciasis in the nearby Amazonia focus of the disease in neighbouring Brazil.