Annals of Tropical Medicine & Parasitology

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Didelphis marsupialis: a primary reservoir of Trypanosoma cruzi in urban areas of Caracas, Venezuela L. Herrera & S. Urdaneta-Morales To cite this article: L. Herrera & S. Urdaneta-Morales (1992) Didelphis marsupialis: a primary reservoir of Trypanosoma cruzi in urban areas of Caracas, Venezuela, Annals of Tropical Medicine & Parasitology, 86:6, 607-612, DOI: 10.1080/00034983.1992.11812716 To link to this article:

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Annals of Tropical Medicine and Parasitology, Vol. 86, No.6, 607-612 (1992)

Didelphis marsupialis: a primary reservoir of Trypanosoma cruzi in urban areas of Caracas, Venezuela BY L. HERRERA AND S. URDANETA-MORALES*

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Instituto de Zoologia Tropical, Seccion de Parasitologia, Facultad de Ciencias, Universidad Central de Venezuela, Apartado 47058, Caracas, Venezuela Received 20 January 1992, Revised 27 July 1992, Accepted 3 August 1992

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 marsupia/is, 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 pseudocysts 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. marsupia/is, as a primary reservoir of T. cruzi, in the establishment of foci of Chagas' disease in Caracas and other Latin American cities, is emphasized.

Trypanosoma cruzi is the haemoflagellate responsible for Chagas' disease, which is widely distributed from the southern United States to northern Argentina. The parasite is transmitted by the haematophagous triatomine bugs (Hemiptera: Reduviidae) which are prevalent in this area (Sherlock, 1979). Chagas' disease is a typical zooanthroponosis, occurring in enzootic foci which may involve domestic animals, and is maintained by the bug vectors that live with domestic and peridomestic animals, including dogs, cats, rats, opossums and bats (Pifano, 1986). The opossum, Didelphis marsupia/is, is widely distributed from eastern Mexico to northern Argentina (Perez-Hernandez, 1989), is frequently found infected with T. cruzi, and is highly adapted to life in intensely-urbanized areas such as the *Author to whom correspondence should be addressed. 0003-4983/92/060607 + 06 $08.0(),/.()

Caracas valley, within which the capital city of Venezuela is rapidly expanding. In the Caracas valley the synanthropic bug Panstrongylus geniculatus feeds on the opossums and acts as the vector ofT. cruzi (Pifano, 1986; Sampson-Ward and Urdaneta-Morales, 1988). As there have been few studies on urban strains of T. cruzi, we are investigating such strains, isolated from P. geniculatus (SampsonWard and Urdaneta-Morales, 1988; De Scorza et a!., 1989) and, in the present study, from mammals caught in highly-urbanized environments in the Caracas valley. MATERIALS AND METHODS

Animals A random sample of mammals was collected from the Los Chorros, Caricuao, El Cafetal, San © 1992 Liverpool School of Tropical Medicine

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Roman and Colinas de Bello Monte zones of the Caracas valley, as delimited by Pifano ( 1986 ). The animals (six black rats, one grey rat, two mice, one sloth, one armadillo, one Proechimys sp., one Caluromys philander and 24 Didelphis marsupia/is) were caught in wire-mesh livetraps placed near human dwellings, using fruit or 'Universal' bait. In addition, six dogs and two cats in the municipal pound, which had been caught in El Cementerio, Coche, El Paraiso, San Juan and Artigas, were also examined. Examination Tail blood from the sylvatic animals (sloth, armadillo, Proechimys, Calurornys, and Didelphis) was examined microscopically as wet smears and as Giemsa-stained thin smears to detect and quantify trypanosome parasitaemias (see Velasquez-Antich, 1968). Each animal was also xenodiagnosed, using 10 third- or fourth-stage laboratory-bred and uninfected nymphs of Rhodnius prolixus. Three or four weeks after the bugs were fed on the mammals their spontaneously-expelled faeces were collected, diluted in 0·85% (w/v) NaCI, and examined microscopically as wet smears. Faecal material found to contain parasites, and further, larger samples of faeces taken (Ryckman, 1954) from the bugs found to be infected, were spread into thin smears, air-dried for 24 hours, and then Giemsa-stained. Haemolymph samples were also taken from the bugs by cutting their tarsi (D' Alessandro, 1976), and examined as wet smears. The positive thin smears of blood and faeces were both examined under oil-immersion ( x 1000). The species of trypanosome was identified according to the criteria laid down by Barretto (1979) and WHO (1986), and the stages of parasite and number of metacyclic forms present in the bug faeces were determined (see Valasquez-Antich, 1968). Mouse Infection Faecal material from each of the bugs used in the xenodiagnosis was inoculated intraperitoneally into 15-g NMRI mice. Tail blood samples from the mice were examined three days after inoculation and then three times weekly until death of the mouse or loss of

parasitaemia, to determine the prepatent period and course of the parasitaemia (see VelasquezAntich, 1968) and the morphology of the bloodstream flagellates. Mortality was recorded daily. To try to maintain each of the trypanosome strains successfully isolated, mice with high parasitaemias were bled by cardiopuncture and the blood from each used to infect three further 10-15 g mice by intraperitoneal injection. The dose of blood was calculated so that each mouse received 104 parasites per gram of body weight. Only one or two passages were made in mice in order to preserve, as far as possible, the biological characteristics of the natural isolate, which can be altered by a long series of passages in animals (Deane et al., 1984). Large numbers of clean bugs, fed upon mice with high parasitaemias, were used to maintain the strains and to determine their infectivity. Tissue Invasion by the Strains The organs of the sylvatic animals, killed by ether overdose, and of infected mice, killed by cervical dislocation, were examined in order to determine the tissue invasion patterns of the strains. Samples of heart, liver, spleen, pancreas, tongue, oesophagus, trachea, stomach, sternum, colon, jejunum, urinary bladder, brain, lung, kidney, lymph nodes, skin, skeletal muscle, prostate, penis, testicle, seminal vesicle, adrenal glands, salivary glands and thymus were fixed in 10% formalin, embedded in paraffin wax, and cut into 5 IJ.m sections. The sections were stained with haematoxylin and eosin and examined for parasites in a double-blind, microscopical study.

RESULTS AND DISCUSSION Trypanosome infections were found in six of the mammals examined, all D. marsupia/is (Table 1). Trypomastigotes, predominantly of the broad form, were seen in the blood smears of two of these animals and were present at a mean density of 1· 28 x 104 per ml of blood. Trypanosome strains were successfully isolated from four of the opossums; all these strains, when inoculated into mice as infected bug faeces,




Description ofthe six Didelphis marsupialisfound infected with trypanosomes in the Caracas valley, Venezuela Test results Specimen no. 1

Colinas de Bello Monte Colinas de Bello Monte El Cafetal Los Chorros Los Chorros San Roman


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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 i...
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