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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 90, Num. 3, 1995, pp. 387-388
Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 90(3): 387-388, may/jun. 1995

RESEARCH NOTE

Presumed Dirofilaria irnrnitis Infections in Wild-Caught Aedes taeniorhynchus and Aedes scapularis in Rio de Janeiro, Brazil

Ricardo Lourenco-de-Oliveira, Leonidas M Deane

Laboratorio de Transmissores de Hematozoanos, Instituto Oswaldo Cruz, Av. Brasil 4365, 21045-900 Rio de Janeiro, RJ, Brazil

Code Number: OC95075
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Key words: Dirofilaria immitis - vectors of canine heartworm - Crithidia - trypanosomatidae flagellates

During the course of studies on the ecology of mosquitoes in the State of Rio de Janeiro (R Lourenco-de-Oliveira 1984 Mem Inst Oswaldo Cruz 79: 479-490), the gut of 569 mosquitoes belonging to 20 species caught in Granjas Calabria, a coastal lowland farm in Jacarepagua, city of Rio de Janeiro, were dissected, as follows: 3 An. albitarsis Lynch-Arfibalzaga, 1878, 29 An. aquasalts Curry, 1932, 292 Ae. scapularis (Rondani, 1848), 48 Ae. taeniorhynchus (Wiedmann, 1821), 6 Ps. confinnis (Lynch-Arfibalzaga, 1891), 1 Ps. pseudomelanota Baram & Cotrim, 1971, 5 Cx. amazonensis (Lutz, 1905), 15 Cx. bidens Dyar, 1922, 1 Culex chidesteri Dyar, 1921, 3 Cx. declarator Dyar & Knab, 1906, 5 Cx. nigripalpus Theobald, 1901, 9 Cx. quinquefasciatus Say, 1823, 25 Cx. saltanensis Dyar, 1828, 2 Cx. ribeirensis Forattini & Sallum, 1985, 3 Cq. venezuelensis (Theobald, 1912), 91 Ma. titillans (Walker, 1848), 9 Ph. deanei Lourenqo-de- Oliveira, 1983, I Ph. theobaidi Lane & Cerqueira, 1942, 3 Wy. forcipenis Lourenco-de Oliveira & Silva, 1985 and 18 Wy. leucostigma (Lutz, 1905).

Mosquitoes with midgut lacking blood were identified to species, dissected in sterile physiological saline and examined microscopically on the day after collection on human or animal baits (R Lourenco-de-Oliveira, R Heyden 1988 Mem Inst Oswaldo Cruz 81: 15-27). Only guts and Malpighian tubules were examined. A compression was done by pressing the guts and Malpighian tubules over with a coveslip in order to squeeze out the detected parasites, which were then Giemsa stained.

Surprisingly, one Ae. taeniorhynchus harbored five active early third-stage nematode larvae free in the lumen of the Malpighian tubules and one Ae. scapularis contained a single sausage-stage larva, also free in the Malpighian tubules. They were presumed to be D. immitis larvae. Presumptive identification was based on morphological characteristics of the filarioid parasites known in the area, according to AER Taylor (1960 J Hehninth 34: 27-38) and PFL Boreham and RB Atwell (1988 Dirofilariasis, C.R.C. Press, Boca Raton, Florida, 249 pp.). The site of development of the worm within the mosquito was also taken in consideration. That is, filariae present in the Malpighian tubules are assumed to be D. immitis, because amongst Oncho- cercidae, only species of the genus Dirofilaria are known to develop within the tubules' cells and lumen (CB Symes 1960 J Hehninth 34: 3942, LL Waltes, MMJ Lavoipierre 1982 J Med Entomol 19: 15-23, DM Sauerman Jr & JK Nyar 1983 Mosq News 43: 222-225, TJ Bradley et al. 1984 J Parasit 70. 82-88, Boreham & Atwell 1988, loc. cit.). Besides, D. immitis is the only species belonging to genus Dirofilaria found in the city of Rio de Janeiro. However, seven other species of filarioid parasites of this genus have been identified in Brazil, whose hosts included man and wild animals (slot, otter, peccary and jaguar) captured outside the city of Rio de Janeiro. D. repens has only once been reported in the State of Sao Paulo. Most of these findings correspond to either single records (some species of doubtful taxonomic status) or poorly described species which have never been found again (H Lent & JFr Freitas 1937 Mem Inst Oswaldo Cruz 32: 37-54/443-448, JM Mendonqa 1948 Mem Inst Oswaldo Cruz 46: 647-651, JFT Freitas & H Lent 1949 Rev Brasil Biol 9: 377- 380, JFT Freitas & LR Mayal 1953 Rev Brasil Med 10: 463467, ND Levine 1968 Nematode parasites of domestic animals and of man, Burgess P. Co., Minneapolis, MG Freitas & HM Costa 1970 Arq Esc Vet 22: 33-94).

Almost 10% of the dogs in Brazil have microfilaremia due to D. immitis. The highest prevalence amongst the localities surveyed in the country has been found in the State of Rio de Janeiro (16.1%, in 1988), essentially in its northern seashore (49%, in 1990) (J Guerrero et al. 1992 Proceedings of the Heartworm Symposium, Austin, Texas, p. 31-36, Am. Heartworm Soc. Publ.). D. im.litis circulating microfilariae have neighborhoods close to Granjas Calabria (N Labanhe, personal communication, GLG Almeida 1981 Reavaliacao da filariose canina no Rio de Janeiro: Epidemiologia e diagnostico. MSc Thesis. UFRRJ, 79 pp.). In spite of canine heartworm being widespread in Brazil and enzootic in some regions, wild-captured mosquitoes had never been examined before to determine the natural vector in the country.

A single infected field collected Ae. taenio- rhynchus and Ae. scapularis does not allow any definitive statements to be made, nevertheless these mosquito species, especially the former, should be considered natural potential vectors of dog heartworm in the coastal lowland areas of Rio de Janeiro. Ae. taeniorhynchus has long been considered a vector of D. immitis in the eastern seaboard of the U.S.A. (KW Ludlan et aI. 1970 JAVMA 157: 1354-1359). JK Nyar and DM Sauerman Jr (1975 J Insect Physiol 21: 1965 -1975) have demonstrated high experimental vec- tor potential in Ae. taeniorhynchus from Florida, which was able to survive and refeeding while heavily infected with D. immitis. These workers later confirmed the involvement of this mosquito in the natural transmission in that area (Sauerman Jr & Nayar 1983 lac. cit.). On the other hand, Ae. scapularis has never been described as potential vector of D. immitis. It has been considered probable vector of Wuchereria bancrofii in southem Brazil (RG Rachou 1956 Rev Bras Malariol D Trop 8: 267-275).

The detection of the presumed D. immitis lar- vae in the Malpighian tubules of Ae. taenirhynchus and Ae. scapularis is epidemiologically im- portant because there are no further barriers to their development at this stage. The larval migration to the Malpighian tubules and survival and development of the prelarvae depend on their capability of surpassing barriers that may hinder its development (Nyar & Sauerman Jr 1975 cit.). Both Ae. taeniorhynchus and Ae. scapularis are considered opportunistic species, feeding on a wide variety of vertebrates, although domestic mammals, especially horses and cows, are their major blood sources in Southeastern Brasil (Lourenco-de-Oliveira, Heyden 1986 loc. cit., OP Forattini et al. 1987 Rev Saade Publ Sao Paulo 21: 171-187). We have never made a serious attempt to evaluate the frequency with which this mosquitoes feed on dogs in Rio de Janeiro, but we have seen dozens of females of both species aggressively attacking these animals several times during our field works. Field studies to know the species composition of mosquito attracted to dogs in enzootic areas as well as on the susceptibility of these insects to D. immitis must be performed to confirm the local vectors.

Additionally, more 371 An aquasalis, 70 Ae. scapularis and 21 Ae. taeniorhynchus collected in Sao Bento, Duque de Caxias (22 43'S 43 16'W), 13 Ae. scapularis, 8 Cx. coronator Theobald, 1903, 26 Ps. ciliata (Fabricins, 1749) and 22 Ps. confinnis caught in Seropedica, Itaguai (22 50'S 43 41'W), and 24 Hg. leucocelaenus (Dyar & Shannon, 1924) captured in Represa do Cigano, Jacarepagua (22 57'S 43 12'W), all in the State of Rio de Janeiro, were also dissected and examined. None of them harbored filarioid larva.

Finally, trypanosomatidae flagellates were found in 16 Ae. scapularis, 2 Cx. saltanensis and 2 Ma. titillans from Granjas Calabria and in 6 Ae. scapularis and 1 Ae. taeniorhynchus from Sao Bento. All trypanosomatids were found in the hindgut, being choanomastigotes (genus Crithidia), except those detected in Ma. titillans which were promastigotes in the midgut. The species of Crithidia found in Cx. saltanensis has been recently described as a new species, C. ricardoi (A Sibajev et al. 1993 Mere Inst OswaMo Cruz 88: 541-546), being morphologically indistinguishable from those found in the 22 infected Ae. scapularis.

Aknowledgements: to Rosemarie Heyden for the assistance in the dissection of mosquitoes, to Rosangela Rodfigues, Joaquim J Vicente and Notma Labarthe for the data on Dirofilaria and heart-worm in Brazil.

Copyright 1995 Fundacao Oswaldo Cruz

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