The escape kinetics from the anterior midgut (AM) of Trypanosoma cruzi during the initial steps of infection was assessed in Triatoma infestans, as well as its ability to survive migration in the digestive tract of the vector. All the four strains evaluated survived and reached variable parasite densities. After 49–50 days, YuYu [discrete typing units (DTU) I] strain reached the highest parasite numbers in the rectum followed by Bug (DTU V), CL-Brener (DTU VI) and Dm28c (DTU I). All strains accomplished metacyclogenesis. Bug strain reached the highest numbers of metacyclic trypomastigotes followed by YuYu and CL-Brener/Dm28c. A remarkable parasite reduction in the AM for Bug strain, but not Dm28c was noticed at 72 h of infection. In the posterior midgut + rectum high densities of parasites from both strains were detected at this period indicating the parasites crossed the AM. For Dm28c strain, in infections initiated with trypomastigotes, parasites left AM faster than those starting with epimastigotes. In conclusion, T. cruzi strains from different DTUs were able to infect T. infestans reaching variable parasite densities. The kinetics of migration in the digestive tract may be affected by strain and/or the evolutive form used for infection.

Triatoma infestans (Klug) (Hemiptera: Reduviidae) is the main vector of Chagas disease in the Southern Cone of America and resistance to pyrethroid insecticides has been detected in several areas from its geographical distribution. Pyrethroid resistance presents a complex geographical pattern at different spatial scales. However, it is still unknown if the toxicological variability is a common feature within villages of the Gran Chaco were high resistance was descripted. The objectives of this study were to determine: (a) the microgeographical distribution of the deltamethrin-resistance in insects from Pampa Argentina village, (b) the performance of the insecticide impregnated paper bioassay to evaluate deltamethrin-resistance in field collected insects and (c) the lethal activity of the fumigant canister containing DDVP against insects resistant to deltamethrin. High survival of T. infestans exposed to discriminant dose was observed in the samples of all the evaluated dwellings, suggesting that the resistance to deltamethrin is homogeneous at the microgeographical level. Resistance determination by impregnated paper bioassay was similar to traditional topical determination, highlighting the use of this rapid methodology in field large-scale monitoring. The fumigant canister was not effective against resistant insects, remarking the need to develop suitable formulations that ensure minimal toxicological risk and high effectivity.

Transmission of Trypanosma cruzi (Kinetoplastida: Trypanosomatidae) occurs when feces/urine of infected triatomines come into contact with mucous membranes or damaged skin, and this occurs mainly when insects defecate while feeding on the host. Thus, the vector competence of the triatomines is associated with their feeding and excretion/defecation behavior. This work studied for the first time the effect of T. cruzi infection on feeding and excretion/defecation patterns of Triatoma infestans (Hemiptera: Reduviidae). Uninfected and infected fifth-instar nymphs were fed ad libitum and their feeding behavior and defecations were registered during and after feeding. The feeding pattern did not show differences between the experimental groups. However, the infected nymphs began to defecate earlier, defecated in greater quantity and there was a greater proportion of defecating individuals compared to uninfected nymphs. These results show that T. cruzi affected the excretion/defecation pattern of T. infestans in a way that would increase the probability of contact between infective feces and the mammalian host.

We assessed the distribution of Trypanosoma cruzi Discrete Typing Units (DTUs) in domestic and peridomestic Triatoma infestans and Triatoma sordida specimens collected in a well-defined rural area in Pampa del Indio, northeastern Argentina. Microscopically-positive bugs were randomly selected with a multi-level sampling design, and DTUs were identified using direct PCR strategies. TcVI predominated in 61% of 69 T. infestans and in 56% of 9 T. sordida. TcV was the secondary DTU in T. infestans (16%) and was found in 1 T. sordida specimen (11%). Three T. sordida (33%) were found infected with TcI, a DTU also identified in local Didelphis albiventris opossums. Mixed DTU infections occurred rarely (5%) and were detected both directly from the bugs' rectal ampoule and parasite cultures. The identified DTUs and bug collection sites of T. infestans were significantly associated. Bugs infected with TcV were almost exclusively captured in domiciles whereas those with TcVI were found similarly in domiciles and peridomiciles. All mixed infections occurred in domiciles. TcV-infected bugs fed more often on humans than on dogs, whereas TcVI-infected bugs showed the reverse pattern. T. sordida is a probable sylvatic vector of TcI linked to D. albiventris, and could represent a secondary vector of TcVI and TcV in the domestic/peridomestic cycle.

The pathogenic flagellate Blastocrithidia triatomae disrupts the digestion of Triatoma infestans; the midgut ultrastructure of bugs infected with the flagellate and of uninfected bugs is compared. Third or fourth instar larvae were dissected either unfed or 1 week after feeding.In all uninfected bugs extracellular membrane layers (e.m.l.) covered the apical microvillar border of the epithelial cells. Some midgut regions of bugs infected with B. triatomae appeared normal but often adjacent cells showed pathological effects. In affected cells the e.m.l. and the microvilli and finally the cells themselves were reduced or destroyed. Correlated with these observations of pathogenicity the method of attachment of parasites changed. When the e.m.l. were present only rarely were flagella found, but on extracellular membrane-free cells B. triatomae attached by flagellar enlargement to the microvillar border or, if this was reduced, to the apical host cell membrane. No hemidesmosome-like plaques were found at the attachment site. Although some flagella were inserted into the apical region of the cells no intracellular flagellates were observed.

Blastocrithidia triatomae parasitizes vectors of Chagas' disease and is very difficult to cultivate in conventional media. However, co-cultivation with a cell line of its host Triatoma infestans (TI-32; in Schneider's Drosophila medium supplemented with 20% foetal calf serum and 10% tryptose phosphate broth) led to vigorous growth at 24 or 28 °C without an adaptation phase. More than 60 primary cultures were initiated successfully without any failures. Subcultures could be started immediately at weekly intervals. The doubling time was similar in both the primary cultures (41 h) and the 33rd subculture (39 h). The importance of the reduviid cells for B. triatomae became clear after removal of the insect cells, when multiplication of epimastigotes stopped and mainly cysts were formed. Cysts produced in vitro were infective for reduviids. Scanning electron microscopy showed that B. triatomae attached to the host cells, inserted its flagellum into them and destroyed them.

The reservoir capacity of domestic cats and dogs for Trypanosoma cruzi infection and the host-feeding patterns of domestic Triatoma infestans were assessed longitudinally in 2 infested rural villages in north-western Argentina. A total of 86 dogs and 38 cats was repeatedly examined for T. cruzi infection by serology and/or xenodiagnosis. The composite prevalence of infection in dogs (60%), but not in cats, increased significantly with age and with the domiciliary density of infected T. infestans. Dogs and cats had similarly high forces of infection, prevalence of infectious hosts (41–42%), and infectiousness to bugs at a wide range of infected bug densities. The infectiousness to bugs of seropositive dogs declined significantly with increasing dog age and was highly aggregated. Individual dog infectiousness to bugs was significantly autocorrelated over time. Domestic T. infestans fed on dogs showed higher infection prevalence (49%) than those fed on cats (39%), humans (38%) or chickens (29%) among 1085 bugs examined. The basic reproduction number of T. cruzi in dogs was at least 8·2. Both cats and dogs are epidemiologically important sources of infection for bugs and householders, dogs nearly 3 times more than cats.

This study applied improved DNA extraction and polymerase chain reaction strategies for screening and identification of Trypanosoma cruzi lineages directly from faeces of triatomines collected in a well-defined rural area in northwestern Argentina. Amplification of the variable regions of the kinetoplastid minicircle genome (kDNA-PCR) was performed in faecal lysates from 33 microscope (MO)-positive and 93 MO-negative Triatoma infestans, 2 MO-positive and 38 MO-negative Triatoma guasayana and 2 MO-positive and 73 MO-negative Triatoma garciabesi. kDNA-PCR detected T. cruzi in 91% MO-positive and 7·5% MO-negative T. infestans, which were confirmed by amplification of the minicircle conserved region. In contrast, kDNA-PCR was negative in all faecal samples from the other triatomine species. A panel of PCR-based genomic markers (intergenic region of spliced-leader DNA, 24Sα and 18S rRNA genes and A10 sequence) was implemented to identify the parasite lineages directly in DNA lysates from faeces and culture isolates from 28 infected specimens. Two were found to be infected with TCI, 24 with TCIIe, 1 with TCIId and 1 revealed a mixed TCI+TCII infection in the faecal sample whose corresponding culture only showed TCII, providing evidence of the advantages of direct typing of biological samples. This study provides an upgrade in the current diagnosis and lineage identification of T. cruzi in field-collected triatomines and shows T. cruziII strains as predominant in the region.

Tetramethrin, deltamethrin and cypermethrin formulated as fumigant tablets or spray(ing) solutions showed flushing out activity on Triatoma infestans. Fumes arising from the tablets were analysed by gas chromatography. The proportion of pyrethroid liberated was between 10 and 20% of the original amount formulated. The flushing out activity shown was dependent on the pyrethroid compound, insect stage and sex. In general deltamethrin proved the most active flushing out agent and cypermethrin the least active. Maximal activity was shown in the combination of nymphs and tetramethrin. Nymphs of Rhodnius prolixus were only flushed out by deltamethrin. In all cases, deltamethrin and cypermethrin yielded 100% mortality 7 days after exposure to the pyrethroid fumes, while tetramethrin was not a killing agent.

The insecticide activity of synthetic pyrethroids to Triatoma infestans was tested by topical application. Deltamethrin, fenpropathrin, bioresmethrin, permethrin, cypermethrin, d-phenothrin and cyphenothrin showed the highest activity.

The susceptibility to poisoning of adult insects by these pyrethroids (except bioresmethrin) was increased by cotreatment with profenofos or with piperonyl butoxide (PBO). Assayed pyrethroids synergized by PBO showed similar general structure.

The vinyl cyano pyrethroids showed a knockdown effect with a delayed recovery. During 15 days after intoxication with deltamethrin, insect recovery was observed. Recovery blockage by PBO was observed in cyphenothrin and deltamethrin poisoning at low doses.

Males of the Triatominae, Panstrongylus megistus and Triatoma infestons, show a considerable difference concerning the time necessary for them to acquire the capacity for the first mating. P. megistus copulates from the eighth day of adult life, irrespective of whether or not it has been fed, while T. infestons copulates about 17 days after the imaginai moult and only after a blood-meal. These differences might be due to the secretory activity of T. infestons male accessory glands whose full development is reached only after two saturant blood-meals. If allatectomy is performed in male P. megistus soon after the imaginai moult, accumulation of secretion does not occur in 3 of the 4 accessory glands. Topical application of precocene II (200 μg/insect)a few days before or soon after the imaginai moult in P. megistus, halves the amount of secretion in the accessory glands.

The detection of household infestations of Triatominae in regions endemic for Chagas' disease is a criterion frequently used in the selection of areas, or of individual houses, for treatment in insecticide campaigns as well as for the evaluation of insecticide performance.

Several methods for the detection of domestic infestations with Triatominae were compared: diurnal capture of live bugs with the aid of a flushing-out agent, night-capture without using flushing-out agents and the use of cardboard boxes of the the Gómez-Núñez type. The flushing-out and Gómez-Núñez box methods were found to be equally sensitive, although each gave several houses as uninfested in which infestation was detected by the other method. The night-capture method was slightly more sensitive but was found to be impractical for large-scale surveys. Improvements to the flushing-out method, notably the introduction of a systematic search technique, made it much more sensitive than the Gómez-Núñez box method for both heavily infested houses and for houses 3 months after insecticide treatment.

Coating the inside surfaces of the boxes with adhesive did not increase the sensitivity of this method and, although this can be achieved by leaving the boxes in place for long periods of time, this also limits the value of the information thus obtained as regards the evaluation of insecticides. On the basis of the results presented, the flushing-out method using a systematic search of the house was found to be the most suitable sampling technique, but it is recognized that this method still has limitations.