Sylvatic Habitats Research Articles

Host preferences ofTriatoma sordida

Triatoma sordida is a widespread vector of Trypanosoma cruzi, living in both sylvatic and domestic habitats. To see if Tri. sordida 'prefers' to feed from avian or mammalian hosts, two experiments were carried out. In the first experiment, in which fifth-instar nymphs were allowed free access to two unrestrained hosts, a guinea-pig and a pigeon, 98% of those feeding fed on the guinea-pig, and the mammalian bloodmeals were generally larger than the avian, with mean weights of 50.9 and 30.2 mg, respectively. In the second experiment, groups of nymphs were exposed to a single host (guinea-pig or pigeon) at two different densities (10 and 30 bugs/host). Whatever the density of the bugs, a much larger proportion of the bugs offered feeds on the guinea-pig took bloodmeals than of those offered the pigeon (55% v. 9%), and the bugs which fed on the mammal again generally took larger bloodmeals (mean weight = 50.9 mg) than the few which fed on the bird (mean weight = 12.8 mg; P < 0.0001). Bug density was found to have a greater effect on the size of the bloodmeals taken from pigeon than on those taken from guinea-pig. Triatoma sordida therefore does not appear to have a marked preference for avian blood; it is probably a generalist species that can invade a variety of habitats to exploit the range of available vertebrate hosts.

Inter-relation of sylvatic and domestic transmission of Trypanosoma cruzi in areas with and without domestic vectorial transmission in Minas Gerais, Brazil.

During the period 1980-1986, we captured triatomine bugs and mammalian reservoir hosts from sylvatic and domestic situations in different municipalities of the State of Minas Gerais. Trypanosoma cruzi was isolated from captured bugs, mammals and patients. After cultivation in LIT medium, the electrophoretic enzyme profiles were determined. We obtained a total of 32 parasite isolates from regions with active domestic transmission, and 24 isolates from areas under control. For the first areas the results suggest introduction of T. cruzi from sylvatic habitats, through incursion of infected opossums and/or sylvatic T. sordida, which appears to have given rise to at least one acute human infection. Of particular interest is the finding of sylvatic opossums and a T. sordida nymph infected with ZB, that could indicate return of parasites from chronic human infections to sylvatic transmission cycles. For the areas under control we also interpret the results as interaction between sylvatic and domestic cycles of transmission, here through the invasion of houses by bugs carrying the Z1 zymodeme from the sylvatic environment. The Multivariate Correspondence Analysis gives a spatial description between the different parasite isolates and confirms the existence of a bridge in the opposite direction in the region with active vectorial transmission including the exporting of Z2 through the peridomestic environment into the sylvatic cycle. For the other areas this bridge corresponds especially to Panstrongylus megistus, importing Z1 into the domestic environment.

Genetic variability and differentiation between populations of Rhodnius prolixus and R. pallescens, vectors of Chagas' disease in Colombia.

Enzyme polymorphism in Rhodnius prolixus and R. pallescens (Hemiptera, Reduviidae), principal vectors of Chagas' disease in Colombia, was analyzed using starch gel electrophoresis. Three geographic locations were sampled in order to determine gene flow between populations and to characterize intra- and interspecific differences. Of 25 enzymes assayed 10 were successfully resolved and then used to score the genetic variation. The enzymes PEPD, GPI, PGM and ICD were useful to differentiate these species and PGD, PGM and MDH distinguished between sylvatic and domiciliary populations of R. prolixus. Both polymorphism and heterozygosity indicated greater genetic variability in sylvatic habitats (H = 0.021) compared to domiciliary habitats (H = 0.006) in both species. Gene flow between sylvatic and domiciliary populations in R. prolixus was found to be minimal. This fact and the genetic distance between them suggest a process of genetic isolation in the domiciliary population.

Parasitic and Phoretic Arthropods of Sylvatic and Commensal White-Footed Mice (Peromyscus leucopus) in Central Tennessee, with Notes on Lyme Disease

Sixteen species of parasitic or phoretic arthropods were collected from 56 white-footed mice, Peromyscus leucopus, live-trapped in central Tennessee from April through November 1987. Arthropod infestation was compared for mice taken from sylvatic (woodland) versus commensal (household) habitats. Three species were recorded from hosts in both habitats: the sucking louse Hoplopleura hesperomydis, the flea Epitedia wenmanni, and the laelapid mite Androlaelaps casalis. Twelve of the 13 remaining arthropod species were taken only from mice trapped in woodland whereas the phoretic glycyphagid mite Glycyphagus hypudaei was collected only from commensal mice. Arthropod faunas on commensal hosts clearly were impoverished. The 12 additional arthropod species recorded from the woodland mice consisted of 1 nidicolous beetle, Leptinus orientamericanus; 1 bot, Cuterebra fontinella; 3 fleas, Ctenophthalmus pseudagyrtes, Orchopeas leucopus and Peromyscopsylla scotti; 1 tick, Dermacentor variabilis; 2 mesostigmatid mites, Androlaelaps fahrenholzi and Ornithonyssus bacoti; 3 chiggers, Comatacarus americanus, Euschoengastia peromysci, and Leptotrombidium peromysci; and 1 undescribed pygmephorid mite of the genus Pygmephorus. Two nymphal and 100 larval D. variabilis were examined for spirochetes and found to be uninfected.

Host Feeding Profiles of Rhodnius Pallescens (Hemiptera: Reduviidae) in Rural Villages of Central Panama *

Rhodnius pallescens, reported to be the principal vector of Chagas' disease in central Panama, has been shown to feed on opossums, anteaters, sloths, rodents, birds and, rarely, lizards in sylvatic habitats in this country; however, the extent of its anthropophagic affinities in rural areas has never been determined. The host selections of 1,340 R. pallescens from domestic and peridomestic habitats of three Panamanian villages were determined by microcapillary precipitin tests. Slightly more than half of the triatomines collected in houses and nearby palm trees and bird nests had fed on humans. Opossums, which are important reservoirs of Trypanosoma cruzi in Panama, were the second most frequently selected host. The importance for the transmission of Chagas' disease to humans of the close relationship between the principal vector and reservoir in sylvatic and peridomestic environments and the anthropophagy of the former is discussed. Pigeons and chickens were the dominant bloodmeal sources of triatomines collected in their respective shelters. The roof rat, Rattus rattus, was the third most common mammalian host, and may represent an ancillary reservoir in the transmission of Chagas' diseases in rural areas of Panama.

Endemic human plague in New Mexico: risk factors associated with infection.

A retrospective case-control study was conducted to identify risk factors, other than contact with infected animal tissues, for infection caused by Yersinia pestis in non-Indian residents of areas with endemic sylvatic plague in New Mexico. The study group consisted of 16 persons who had bacteriologically confirmed cases of plague in the period 1975-1976 and 45 controls who were matched by age, sex, and location of residence. Participants were questioned about outdoor activities, environmental conditions in and around the home, procedures of pet care, exposure to animals and insects, and medical history. The availability of harborage and food sources for wild rodents as a result of human activity in the immediate home environment was associated with risk of infection. Failure to take steps to control fleas on dogs and cats also appeared to be a possible risk factor. No other significant differences were found between patients and controls. Plague in New Mexico appears to result primarily from entry of the reservoir host into the habitat of the human rather than from entry of the human into the sylvatic habitat of the reservoir host.

An outbreak of acute Chagas's disease in the São Francisco Valley region of Bahia, Brazil: triatomine vectors and animal reservoirs of Trypanosoma cruzi

Following reports of an unusually high incidence of acute Chagas's disease and the appearance of large numbers of Triatoma infestans in the southwestern region of the State of Bahia, triatomine bugs (Hemiptera: Reduviidae) and domestic animals in one of the affected communities were surveyed and examined for infection with Trypanosoma cruzi. Triatoma infestans was prevalent in houses and was also found in peridomestic habitats. T. sordida and T. pseudomaculata occupied peridomestic and sylvatic habitats and T. brasiliensis was found only among rocks far from houses. Panstrongylus megistus, formerly present in the region, was not found. Trypanosoma cruzi was detected in 19·5% of Triatoma infestans, 11·5% of T. sordida, 19% of dogs, 29% of cats and 100% of rats examined. A disproportionate number of early instar bugs were infected with Trypanosoma cruzi, suggesting that a rapid increase in the rate of transmission had recently occurred. The history of the domestic triatomine fauna of the region since 1912 is reviewed, and it is proposed that the relatively recent arrival of Triatoma infestans initiated a domestic cycle linked to peridomestic and sylvatic cycles of Trypanosoma cruzi transmission. Increased human mobility, the use of DDT for malaria control, and drought conditions are considered as factors which might have contributed to the outbreak of human infection.

The prevalence of trypanosomes and microfilariae in Panamanian monkeys.

A total of 3,523 wild caught monkeys from Panama was examined for blood parasites from August 1968 through June 1972. Trypanosomes or microfilariae were observed in the blood of 31.1% of the monkeys. Mixed infections, with microfilariae and trypanosomes, were detected in 6.6% of the animals. Trypanosoma cruzi was found in marmosets. Saguinus geoffroyi (12.2%), in white-faced capuchins, Cebus capucinus (5.0%), in squirrel monkeys, Saimiri sciureus (1.7%) and in black spider monkeys, Ateles fusciceps (1.2%). Trypanosoma rangeli was found in S. geoffroyi (55.8%) and C. capucinus (12.5%). Other trypanosomes found in Panamanian monkeys included T. minasense, and T. mycetae. Saguinus geoffroyi showed the highest infection rate (88.9%) with trypanosomes and/or microfilariae; trypanosomes were seen in 68.1%, and microfilariae in 73.0%, of the animals examined. The marmosets, white-faced capuchins, and squirrel monkeys should be considered as significant hosts of T. cruzi in sylvatic habitats and may serve as reservoir hosts of Chagas' disease in Panama. The microfilariae seen in monkeys from Panama were tentatively identified as larval forms of Dipetalonema gracile in Aotus trivirgatus; D. obtusa in C. capucinus and S. geoffroyi; and D. marmosetae in Alowatta villosa, C. capucinus, A. trivirgatus, S. sciureus, A. fusciceps, and S. geoffroyi.