Infected Bugs Research Articles

Infectivity to the vector Triatoma infestans of dogs infected with Trypanosoma cruzi in north-west Argentina.

The influence of reinfections on the infectivity to Triatoma infestans of dogs seropositive to Trypanosoma cruzi was investigated in Amamá, north-west Argentina, before (1984) and after (1986-1987) elimination of domestic bugs with residual insecticides in 1985. Infectivity was quantified by the percentage of infected bugs in each xenodiagnosis of a seropositive dog, i.e. the infective force (IF). Exposure to reinfection was represented by the domiciliary density of infected bugs and by an index of the potentially-infective contacts (IPIC) experienced by each dog (calculated as the product of the relative density of bugs per dog, the proportion of infected bugs, and the proportion of bugs taking blood meals from the dog). IF was unrelated to the dog's age or sex, or the level of specific antibodies to T. cruzi. Before vector elimination, the IF of seropositive dogs was significantly associated with both the density of infected bugs and the IPIC. After vector elimination, seropositive dogs resident at houses which had 10-70 infected bugs before spraying showed a higher median IF (67-75%) than those living in houses with zero to eight infected bugs before spraying (47-55%). The age-specific IF of seropositive dogs aged one year or older, recorded before (45-64%) and after (52-56%) the elimination of domestic bugs, did not differ significantly. Our data suggest that the infectivity of seropositive dogs to bugs is modified by previous or current exposure to bug-mediated reinfections, and that this relationship might be irreversible in the short term.

Didelphis marsupialis: a primary reservoir of Trypanosoma cruzi in urban areas of Caracas, Venezuela.

Direct blood examination and xenodiagnosis of 45 sylvatic, peridomestic or domestic mammals from the Caracas valley, Venezuela, revealed trypanosome infection in six of the 24 opossums, Didelphis marsupialis, collected in urban areas. Isolates were successfully made of trypanosomes from four of the opossums, using the parasites which developed in Rhodnius prolixus fed on the infected opossums to infect NMRI mice. The prepatent period, course of parasitaemia, morphology of bloodstream trypomastigotes, tissue tropism of parasites in the opossums and/or mice, host mortality, morphology of parasites in the bugs, and infectivity to mice of parasites in the faeces of infected bugs, were all characteristic of Trypanosoma (Schizotrypanum) cruzi. In mice, the parasites showed marked myotropism; the heart, skeletal muscle and the smooth muscle of the urinary bladder, penis, prostate, seminal vesicle, lung, stomach, jejunum and colon were frequently invaded, and pseudocyts were also occasionally found in the liver, brain and pancreas. The significance of the invasion of the genito-urinary structures as a possible alternative parasite transmission route is discussed. The possible role of D. marsupialis, as a primary reservoir of T. cruzi, in the establishment of foci of Chagas' disease in Caracas and other Latin American cities, is emphasized.

Possible oral transmission of acute Chagas' disease in Brazil

In October 1986, 7 to 22 days after a meeting at a farm in Paraíba state, 26 individuals presented with a febrile illness associated with bilateral eyelid and lower limb edema, mild hepatosplenomegaly, lymphadenopathy and, occasionally a skin rash. A 11-year-old boy exhibited atrial premature complexes and a 74-year-old patient developed acute heart failure. In two patients hospitalized in São Paulo city, acute Chagas' disease was diagnosed by the demonstration of circulating Trypanosoma cruzi. At autopsy in a fatal case, acute Chagas' cardiomyopathy was demonstrated. Xenodiagnosis were positive in 9 out of 14 tested patients. A specific IgG immune response was found in all patients and specific IgM antibodies were identified in 20 out of 22 tested patients. A epidemiological survey showed the existence of Triatoma brasiliensis in the outbuildings of this farm, but none in the house where most of the guests stayed. A high rate of infection with Trypanosoma cruzi was found in opossums. These observations together with those related to the food consumed by the patients, lead the authors to suggest that the human infections resulted from oral contamination probably originating from naturally infected marsupials in the area or crushed infected bugs.

Infection of chinch bug, Blissus leucopterus leucopterus (Hemiptera: Lygaeidae), adults from Beauveria bassiana (Deuteromycotina: Hyphomycetes) conidia in soil under controlled temperature and moisture conditions

Infection of adult chinch bugs, Blissus leucopterus leucopterus, from Beauveria bassiana conidia contained in soil was investigated in the laboratory under controlled temperature and moisture conditions. Chinch bug infection was related positively to the concentration of B. bassiana in soil. Soil moisture did not significantly affect the initiation of infections at 20°C, but at 30°C, a proportionately greater percentage of chinch bugs became infected when exposed to drier soils. Mortality of infected chinch bugs occurred the fastest among bugs that had been exposed to the combination of high temperature and high soil moisture. The survival of B. bassiana conidia in soil was affected adversely by increasing soil temperature and moisture.

Pathological effects of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bug Triatoma infestans after infection by membrane feeding and long-tern starvation

Developmental time and mortality in larvae of the reduviid bug Triatoma infestans were studied in uninfected groups and in those infected with Blastocrithidia triatomae by in vitro feeding with 10 4 cyst stages/cm 3 blood. Bugs were subsequently subjected to two different starvation periods. In bugs fed at weekly intervals infection with B. triatomae was associated with developmental retardations, increasing in the final instars, and with increased mortality in the third and preadult instar. Compared to these groups, long-term starvation caused slightly lower mortality rates of uninfected groups and in infected bugs a remarkably higher mortality rate in the preadult instar. Total mortality rates of infected groups were nearly unaffected by starvation.

The effect of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bug Triatoma infestans: Influence of group size

Developmental time and mortality in uninfected larvae of the reduviid bug Triatoma infestans and in those infected by feeding a mixture of blood and cysts of the homoxenous trypanosomatid Blastocrithidia triatomae were compared. Larvae were maintained isolated in 77-cm 3 (area 9.6 cm 2) beakers or in groups of 20, 30, 40, and 50 bugs per 1-liter beaker (area 722 cm 2). In uninfected groups, only a minor proportion of isolated bugs showed delayed development, but in groups infected with B. triatomae, additionally, a retardation in groups of 50 larvae occurred. Infected bugs needed more time to complete development in fourth and fifth instar than did uninfected bugs. Mean mortality rates of about 10% in uninfected groups were unaffected by group size. Mortality rates in most groups of infected bugs were about 50%, but in groups consisting of 50 larvae a statistically significant higher mortality rate of 75% was observed. This indicates a subpathological overcrowding stress, increased by the synergistic action of the flagellate.

Seasonal changes in infectivity of domestic populations of Triatoma infestans

This paper examines the infection rate of Trypanosoma cruzi in Triatoma infestans, the main vector of Chagas disease in Argentina and neighbouring countries. The study was carried out in 1986–1987 on 5 houses ( ranchos) in the endemic area of central Argentina. Domestic T. infestans populations were sampled in each season with a constant capture effort (2·5 man-hours/house) using a chemical irritant. The rectal content of the bugs was examined for the presence of T. cruzi. The vector population density showed seasonal changes with highest values during the hot season (November–April). The percentage of infected bugs was higher in mid-spring (November) and autumn (April) than in winter (August) and early spring (October). The mean number of parasites (epimastigotes and trypomastigotes) per μl of rectal material was very high during mid- and late spring (December). The percentage and number of metacyclic forms differed between seasons, reaching the highest values in late spring. The percentage of infected bugs in houses with children younger than 10 years old was higher than that in houses without children, during all the seasons. Late spring seemed to be the period when domestic populations of T. infestans had the highest vector potential.

Developmental time and mortality of the reduviid bug Triatoma infestans with differential exposure to coprophagic infections with Blastocrithidia triatomae (Trypanosomatidae)

Developmental time and survival in larvae of the reduviid bug Triatoma infestans were studied in uninfected groups and in those exposed to a coprophagic infection with Blastocrithidia triatomae. Addition to young uninfected larvae of (a) different numbers of infected bugs, (b) infected and uninfected bugs, and (c) fresh or dry infectious feces were compared. Retardation of development was evident in groups given infected larvae or fresh feces. Mortality rates were correlated with infection rates and were higher in groups given more infected bugs, independent of the presence of uninfected bugs. Therefore, bugs did not discriminate between feces from infected and uninfected bugs, or they did not reject infectious feces. Dry feces had to be redissolved with fresh feces before infection was possible.

Membrane feeding for infection of the reduviid bugTriatoma infestans withBlastocrithidia triatomae (Trypanosomatidae) and pathogenic effects of the flagellate

To investigate the pathogenic effects of the trypanosome Blastocrithidia triatomae on Triatoma infestans, a method for direct infection by in vitro feeding was developed. After isolation of B. triatomae cysts from infected dead bugs, a suspension of cysts was disinfected with Desogen and Chloramin T, then mixed with sterile blood, spread on a sterile, parallel-grooved glass plate or a hammered aluminium plate and covered with a thin, sterile silicone membrane. The blood and plate were warmed to 36 degrees-38 degrees C by a heating plate. For investigation of the pathological effects, first instars of T. infestans were allowed to feed through the membrane on a mixture containing 10(6) cyst stages/cm3 blood. Development of about 30% of the third and fourth instar larvae was retarded as compared with that in uninfected control groups, and mortality rates increased in fourth and/or fifth instar larvae. Whereas total mortality rates of about 5% occurred in control groups, about 85% of the larvae died in the infected groups. These effects are very similar to those obtained in previous studies with coprophagic infections.

Development and interactions ofTrypanosoma rangeli in and with the reduviid bugRhodnius prolixus

Two strains of Trypanosoma rangeli and three strains of Rhodnius prolixus were used in various combinations to transmit the trypanosomes via the reduviid bug. A persisting infection in the midgut lumen posterior to the stomach resulted in all 2,500 bugs being third and fourth instars. Infectious, metacyclic forms developed exclusively in the salivary glands; forms excreted with bug feces were noninfectious to mice. The midgut epithelium was the main barrier to transmission of the parasite. In only 2%-5% of the infected bugs was it penetrated, and no correlation with any parameter tested could be found. The trypanosomes passed through the gut epithelium by an intracellular route; they were contained in a parasitophorous vacuole. The salivary glands of R. prolixus were found to be infected whenever the hemolymph was infected, after a successful penetration of the gut epithelium, or after injection of T. rangeli. On the other hand, hemolymph infections in Triatoma infestans were eliminated within a few days, and the salivary glands of this bug were never invaded. Pathogenic effects of T. rangeli on R. prolixus could be seen in midgut epithelial cells by a loss of cytoplasm and in muscle and salivary gland cells by very high parasite densities. However, as the penetration rate of the gut is low, T. rangeli is not likely to prove to be efficient in natural control of R. prolixus.

Transmission and Ecology of Trypanosomatid Flagellates of Water Striders (Hemiptera: Gerridae)

An investigation of transmission and ecology of the monogenetic trypanosomatids, Blastocrithidia gerridis and Crithidia flexonema, in Gerris is described. Motile free-living flagellates of both species were found in the faeces of Gerris and in the water on which the bugs inhabited. Transmission of both trypanosomatid species occurred from naturally infected wild-caught bugs to flagellate-free laboratory-bred bugs via water. Crithidia flexonema was also transmitted to laboratory-bred bugs after being isolated in culture. Observations of experimentally infected bugs indicate that C. flexonema flagellates are imbibed and pass through the fore- and midgut to the hindgut where they become attached and multiply. There was no evidence to suggest transovarial transmission. In a 3-yr investigation into the prevalence of trypanosomatids in a natural population of adult Gerris odontogaster, it was found that the infection rate varied between 19% and 100%. There was no significant difference in infection rates between females and males. The infection rate peaked for each year in late spring or early summer. The significance of these results is discussed in relation to the ecology and behaviour of Gerris. The results indicate that the infections are maintained in hibernating bugs over winter.

Cannibalism and Coprophagy Are Modes of Transmission of Blastocrithidia triatomae (Trypanosomatidae) between Triatomines

Transovarial transmission was not detectable among Blastocrithidia triatomae-infected Triatoma infestans. Rather, B. triatomae was transmitted directly between triatomines by cannibalism and coprophagy. Cannibalism conditions that excluded coprophagy always resulted in an infection of Dipetalogaster maxima. The efficiency of transmission was not influenced by the blood source--mice or chickens--fed to the infected donor bugs although chicken blood lyses the epimastigotes of the stomach population. Triatoma infestans was infected by coprophagy only if fed, not if unfed. Blastocrithidia triatomae in dry feces was taken up only if the feces were redissolved in fresh feces. Infections also appeared in groups of bugs fed on chickens previously used for feeding infected bugs.

Parasite/host-interrelationships of the trypanosomatids Trypanosoma cruzi and Blastocrithidia triatomae and the reduviid bug Triatoma infestans: influence of starvation of the bug

We have investigated the effects of Trypanosoma cruzi and Blastocrithidia triatomae on the life span of starved second/third (L2/3), third/fourth (L3/4), and fourth/fifth instars (L4/5) of Triatoma infestans, which had been infected in the first instar and fed last in the second, third or fourth instar respectively. The intestines and sometimes also the flagellate populations of dead bugs were examined. In uninfected L2/3 a higher relative humidity prolonged the life span. With a maximal survival of 14 months, uninfected L3/4 were the most resistant to starvation, followed by L4/5 and then L2/3. Trypanosoma cruzi reduced the life span of starved L3/4 and L4/5 by only 14% and 17%, respectively. Infection with B. triatomae reduced life spans by 51% (L2/3), 55% (L3/4) and 32% (L4/5). The intestines of dead infected bugs were more likely to contain incompletely-digested blood remnants than those of uninfected bugs; living flagellates occurred in all parts of the intestine, and often the rectal lumen contained more dead flagellates than were found on the rectal wall.

Trypanosoma (Megatrypanum) incertum from Pipistrellus pipistrellus: development and transmission by cimicid bugs.

Trypanosoma (Megatrypanum) incertum Pittaluga 1905 was found in 33 out of 206 Pipistrellus pipistrellus caught at various sites in Britain. The trypanosome is described from blood smears. Development took place in laboratory-reared Cimex pipistrelli and Cimex lectularius. Epimastigote forms initially multiplied rapidly in the ventriculus and midgut of Cimex. Metacyclic trypanosomes were found in the rectum of both species of Cimex after 8 days when bugs were maintained at 20 degrees C and as early as 3 days at 30 degrees C. Electron microscopy of infected bugs revealed that there was no attachment to epithelial cells of the ventriculus or midgut, but within the rectum epimastigotes were attached by their flagella to the cuticle of the rectum by hemidesmosomes. Transmission was achieved by feeding experimentally infected bugs to bats kept in the laboratory. These bats were negative as judged by xenodiagnosis using laboratory-reared Cimex. Bats which had been caught in the wild demonstrated low-grade or sub-patent parasitaemias (positive in xenodiagnosis) for up to 400 days after the day of capture. Despite an extensive search of impression smears of tissues immediately after trypanosomes first appeared in the blood of experimentally infected bats no multiplicative stages were found.

The influence of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bug Triatoma infestans: in vivo and in vitro diuresis and production of diuretic hormone.

The homoxenous flagellate Blastocrithidia triatomae disturbs excretion in Triatoma infestans. During the first 4 and 24 h after feeding, infected 5th instars excreted approximately a 2.5-fold smaller volume of urine. Consequently, about double the normal volume of haemolymph could be obtained from these infected bugs 24 h after feeding. Surprisingly, the in vitro secretion rates of Malpighian tubules from uninfected and infected bugs were nearly identical. In addition, the storage and release of diuretic hormone in infected bugs was sufficient to induce normal secretion rates by isolated Malpighian tubules. Therefore, the previously observed ultrastructural alterations in the upper Malpighian tubules of infected bugs do not result in a disturbed in vitro secretion, although in vivo excretion is reduced.

Developmental time and mortality in larvae of the reduviid bugs Triatoma infestans and Rhodnius prolixus after coprophagic infection with Blastocrithidia triatomae (Trypanosomatidae)

Infections with the homoxenous flagellate Blastocrithidia triatomae did not influence the developmental time or mortality rate of the larvae of groups of Rhodnius prolixus. However, Triatoma infestans was severely affected if first instars were maintained together with infected bugs. There was a retardation of larval development and increase of mortality starting in some third instars. Mortality rate during larval development was 75% higher in B. triatomae groups than in the control groups. Infected T. infestans also showed disturbances in digestion, excretion, and tanning.

Developmental time and mortality of larvae of Triatoma infestans infected with Trypanosoma cruzi

Triatoma infestans were infected with Trypanosoma cruzi (zymodeme 1) at the first feed after eclosion from the egg; interstadial development times and mortality rates were then recorded until the imaginai moult and compared with those of uninfected controls. No retardation of development occurred in infected bugs and their mean total mortality rate (9%) was only slightly higher than that (6%) of uninfected controls (due solely to 4 additional deaths). This is the first demonstration, under optimal and standardized rearing conditions, that infection of T. infestans with T. cruzi has little or no effect on development times or mortality rates.

Influence of Blastocrithidia triatomae (Trypanosomatidae) on the reduviid bug Triatoma infestans: alterations in the Malpighian tubules.

To investigate the cellular basis of our recent observation that the trypanosome Blastocrithidia triatomae disturbs excretion in Triatoma infestans, we compared the morphology and ultrastructure of Malpighian tubules in infected and noninfected bugs. Tubules of bugs infected 3-4 months before dissection did not show any morphological alterations in either the upper or lower regions. In fifth instars with a long lasting infection (9-10 months) and a correspondingly retarded larval development, the tracheal system supplying the Malpighian tubules was reduced and alterations were conspicuous in the upper region, where the tubules were slightly widened, sometimes having parts with conspicuous swellings. The cells were filled with white concretions and a strong autofluorescence was evident by fluorescence microscopy. Transmission electron microscopy demonstrated an increase in the number of these concretions, even after short infection periods. In the extremely swollen parts of the tubules there was a reduction in basal cell interdigitations, mitochondria, and microvilli. B. triatomae (but also gram-negative bacteria) occurred only in these swollen parts.

Studies on Trypanosoma rangeli Tejera, 1920. IX. Course of infection in different stages of Rhodnius prolixus.

Frequent individual observations od different stages of Rhodnius prolixus exposed to Trypanosoma rangeli, revealed a higher susceptibility to infection in the bugs exposed during the two first instars. The mortality rate in infected bugs was significantly higher than in controls, indicating that the parasite was responsible for the majority of deaths. An analysis of the mortality distribution, per instar, is presented. Statistical analysis of deaths among the different infected instars, showed that T. rangeli produces its pathological effect in any stage of R. prolixus independently of its susceptibility to the parasite. The survival to adult decreased in all the infected instar bugs. A significant longer time to reach the adult stage was observed in the infected bugs when compared with controls, excepting for specimens exposed in the third instar. The epidemiological significance of the present results is discussed.

Dynamics of transmission of Trypanosoma cruzi in a rural area of Argentina. III. Persistence of T. cruzi parasitemia among canine reservoirs in a two-year follow-up.

A new cross-sectional survey of household- associated mongrel dogs as well as follow-up of previously parasitemic individuals was carried out in 1984 toy means of xenodiagnosis and serologic techniques to get a deeper insight into the relationship of T. cruzi parasitemia and age among canine hosts in a rural area of Argentina. Persistence of detectable parasitemia was age-independent, or at most, loosely related to age, confirming the pattern observed in 1982. Similarly no significant age-decreasing effect was recorded among seropositive dogs in: a) the probability of detecting parasites in a 2-year follow-up; b) their intensity of infectiousness (=infective force) for T. infestans 3rd-4th instar nymphs, as measured by the percentage of infected bugs observed in each dog xenodiagnosis. Moreover, not only was the infective force of seropositive dogs for bugs approximately constant through lifetime, but it was significantly higher than the one recorded for children in the present survey, and for human people by other researchers. Therefore, and since T. infestans field populations show high feeding frequencies on dogs, the latter are expected to make the greatest contribution to the pool of infected vectors in the rural household of Argentina. This characteristic should be sufficient to involve canine reservoirs definitely as a risk factor for human people residing in the same house. The increased severity of parasitemia observed among dogs in this survey may be related to the acute undernutrition characteristic of canine populations of poor rural areas in our country, which is expected to affect the ability of the host to manage the infection.