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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
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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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