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Survey of Dirofilaria immitis (Leidy, 1856) in random source cats in metropolitan Rio de Janeiro, Brazil, with descriptions of lesions
veterinary parasitology ELSEVIER
Veterinary Parasitology 71 (1997) 301 -306
Survey of Dirofilaria immitis (Leidy, 1856) in random source cats in metropolitan Rio de Janeiro, Brazil, with descriptions of lesions Norma Labarthe a,,, Ana Maria Reis Ferreira b Jorge Guerrero c Kathleen N e w c o m b c, Elan Paes-de-Almeida b a Faculdade de Veterinfria, Universidade Federal Fluminense, Rua Vital Brazil Filho 64, 24230-340, Niterf~i, Rio de Janeiro, Brazil b Departamento de Patologia, Unil~ersidade Federal Fluminense, Rua Marquez do Paran6, 300 Niter6i. Rio de Janeiro, Brazil c Merck and Co, Inc., P.O. Box 2000, Rahway, NJ, 07065-0912, USA
Received 13 January 1997; accepted 25 February 1997
Abstract To evaluate the prevalence of heartworm disease in metropolitan Rio de Janeiro, RJ, Brazil, cats submitted for euthanasia were evaluated by laboratory tests and by necropsy for signs of heartworm infection. Of the 125 cats examined, one (0.8%) - - a stray male from an urbanizing district - - had one male worm (14.5 cm) in the left lung and showed severe muscular hypertrophy of small pulmonary arteries and arterioles with no right ventricle enlargement or passive congestion. Microfilariae were not detected in the blood of any cats. The prevalence of canine heartworm in the area from which this cat originated is estimated to be approximately 12%. The prevalence of canine heartworm in the urban area of Rio de Janeiro has been determined to be approximately 5%. It has been shown that the prevalence of feline heartworm disease parallels that in dogs, but at a lower rate. Results of this survey strongly suggest that heartworm prevention measures should be taken under consideration, especially among cats living in a high canine heartworm prevalence area. © 1997 Published by Elsevier Science B.V. Keywords: Dirofilaria immitis; Heartworm; Cat; Feline
* Corresponding author. Gustavo Sampaio 194/1101, Leme, 22010-000, Rio de Janeiro, RJ-Brazil. Fax: +55 21 2952052. 0304-4017/97/$17.00 © 1997 Published by Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 4 0 1 7 ( 9 7 ) 0 0 0 4 1 - 1
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1. Introduction Once believed to be a rare parasite of cats, Dirofilaria immitis is diagnosed with greater frequency today. Although cats are not considered normal hosts of D. immitis, they are indeed susceptible to heartworm infection and it is recognized that it is likely to be a life-threatening disease in cats (Donahoe, 1975; McCall et al., 1994; Mansour et al., 1995). The perception of increased prevalence of feline heartworm disease could be either due to better diagnostic skills and awareness of veterinarians, or because more cats are becoming infected by D. immitis (Guerrero et al., 1992). Although diagnostic tests are improving, feline heartworm is still difficult to detect and estimates of the prevalence are likely to be inaccurate (Rawlings, 1986). The majority of infected cats are amicrofilaremic and low worm burdens are also characteristic of feline heartworm infections, which make it difficult for detection using microfilarial or ELISA antigen tests (Courtney and Zeng, 1987; Guerrero et al., 1992). An ELISA antibody test has been considered helpful in the diagnosis of heartworm infections in feline patients, but the reliability of this test is still being investigated (McCall et al., 1995). One of the most important antemorten diagnostic procedures in the cat is the radiographic examination of the thorax. The detection of enlarged lobar arteries suggests a positive heartworm diagnosis (Lewis, 1986). Feline heartworm prevalence generally parallels that in dogs at a given location, but at a lower rate (Otto, 1974; Dillon, 1984). The first report of feline heartworm infection seems to have been from Brazil (Travassos, 1921), followed by a second report in 1922 from USA (Riley, 1922). Recently, several reports from around the world have been documented in two reviews (Dillon, 1986; Ryan and Newcomb, 1995). Since the initial report in 1921, little information has been published on feline heartworm infections in Brazil. In Rio de Janeiro City, Chagas et al. (1989) reported a worm found in a cat during necropsy and in S5o Paulo state, Nunes (1992) reported 12 infected animals out of 24 cats examined in a heavily enzootic canine heartworm area. Eleven of these 12 cats were diagnosed by ELISA antigen tests and one case was discovered by necropsy. In Rio de Janeiro, the prevalence of canine heartworm is estimated to range from 16 to 21% (Guerrero et al., 1989; Labarthe et al., 1990). When the area is split into sections according to the urbanization pattern, the urban area shows a prevalence of nearly 5%, urbanizing districts show 12%, and the rate in suburbs is around 33% (Labarthe et al., 1992). The present survey was initiated to update data on feline heartworm in Rio de Janeiro City.
2. Materials and methods 2.1. Experimental animals
From April 1993 to April 1994, 125 adult cats, including 87 females and 38 males from the metropolitan Rio de Janeiro, RJ, Brazil, were selected at random from those scheduled for euthanasia. Each animal was uniquely identified, and all available information on the animal was recorded. Animals were handled considering their
N. Labarthe et al. / Veterinary Parasitology 71 (1997) 301-306
303
welfare throughout the trial procedures. The districts from which cats originated were classified according to the urbanization pattern as either urban or in the process of becoming urbanized. 2.2. Blood sample collection and testing From each cat, a blood sample was drawn in a tube containing EDTA. After collection of blood, each animal was given 10000 IU heparin by intravenous injection. Blood samples were examined by a modified Knott test (Newton and Wright, 1956) to detect microfilariae. 2.3. Necropsy examinations Approximately 3 min after the injection of heparin, an intravenous injection of euthanasia solution was administered to the cat. Necropsies were performed at Faculdade de Veterinfiria, Universidade Federal Fluminense. During necropsy, the pleural and peritoneal cavities were examined for the presence of D. immitis, then the lungs and heart were removed, dissected and thoroughly examined. All worms found were removed, identified by sex, measured, enumerated and stored in acetic 10% formalin solution.
3. Results All cats evaluated were amicrofilaremic. At necropsy, one of the 125 cats examined (0.8%) had live D. immitis adult worms. The infected cat was a male stray from an
Fig. 1. Muscular hypertrophy and hyperplasia of the branch of the caudal pulmonary artery with villous projection of the intima and partial obstruction of the arterial lumen. (HE, 100X negative).
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urbanizing district, and was thin, weak and very dirty when presented for euthanasia. When data were evaluated by sex, the prevalence was 0% (0/87) in female cats and 2.6% (1/38) in males. According to the type of environment the cat had originated from, prevalence was 0% (0/62) for the urban area and 1.6% (1/63) in the urbanizing districts. The worm recovered from this cat was a mature live male, measuring 14.5 cm in length and was located at the apical region of the cranial portion of the left lung lobe. Both lungs were grossly congested. Histopathological findings included rows of villous projections of the intima into the lumen, diffuse thickening of the subintima and myointimal proliferation with muscular hypertrophy and hyperplasia of the branches of the caudal pulmonary arteries, producing partial obstruction of the arterial lumen (Fig. 1). Other microscopic changes observed were congestion, edema and a discrete adventitial and perivascular inflammatory infiltration of polymorphonuclear and mononuclear cells.
4. Discussion The presence of one adult worm in the apical region of the cranial portion of the left lung, and the severity and distribution of the arterial lesions found in this cat, suggest that the lesions could have been produced by migration of the live worm through the vessels, as has been previously observed (Doi et al., 1982; Horioka et al., 1984; Comell et al., 1988; McCall et al., 1994). Embolic dead adult D. i m m i t i s in the pulmonary artery, characterized by thrombus formation, organization and intimal granuloma that are frequently observed in dogs and cats (Doi et al., 1982; Knight, 1987; McCall et al., 1994 and Calvert et al., 1994), were not observed in the infected cat in this survey. Embolization is a cause of sudden death in infected cats and may be accompanied by severe acute pulmonary hypertension (Knight, 1987). The muscular hypertrophy of small pulmonary arteries and arterioles observed in this cat has also been observed in some normal cats, but is a consistent finding in cats infected with heartworms (Rawlings et al., 1990; McCall et al., 1994 and Calvert et al., 1994). Compensatory hypertrophy and enlargement of the right ventricle and the subsequent systemic passive congestion are familiar findings in canine dirofilariasis and are uncommon developments in cats (Knight, 1987; Doi et al., 1982). They were not evident in this feline case, most likely because the present infection was limited to a single worm. Therefore, it seems that severe chronic pulmonary hypertension is not a common feature of cats with heartworm disease, probably due to the low number of worms usually harbored by them (Knight, 1987). The heartworm-infected cat of this survey came from the urbanizing area, where canine infections are frequently encountered (12%). This suggests that, as in other countries, infection rates for heartworm in cats tend to parallel those in dogs. This is particularly evident in the urban area, where only 5% of the dogs are reported to be infected (Labarthe et al., 1992), and no feline infections were detected in this survey. It
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has been reported by others that male cats seem to be more often infected with D. immitis than females (McCall et al., 1992 and Donahoe, 1975). Findings in the present survey provide additional evidence that this may be true. Although it is generally accepted that the prevalence in cats parallels that in dogs, but at a lower rate, it is interesting to note that in Rio de Janeiro, where canine heartworm infection ranges from 16 to 21%, heartworm infections were detected in 0.8% of the cats evaluated in the present study, while in northern Italy, the prevalence of canine heartworm infection averages around 40%, and in a survey conducted by Genchi et al. (1992), 12.5% of 120 household and stray cats in the area were infected with heartworm. It is conceivable that either cats or worms, or possibly both, have genetic differences to create such a disparity between the two countries, or there may be some correlation with the mosquito vectors, as suggested by Genchi et al. (1992) and Holmes et al. (1992). In any case, the present survey provides further evidence that feline heartworm disease should be given serious consideration in areas known to have a high prevalence of canine heartworm.
Acknowledgements The authors acknowledge Prof. Sebasti~o Jos6 de Oliveira and Prof. Ricardo Louren~o de Oliveira for their support and criticism of the manuscript.
References Calvert, C.A., Rawlings, C.A., McCall, J.W., 1994. Feline heartworm disease. In: Sherding, R.G. (Ed.), The Cat Disease and Clinical Management, 2 "d edn., Vol. 1. Churchill Livingstone, New York, 623-645. Chagas, W.A., Courtino, V., Pimenta, A.L.P., Ribeiro, V.L.S., D'Almeida, S.R.M.J., 1989. OcorrSncia de dirofilariose em Felis cati. In: Anais do I Congresso Internacional de Zoonoses, Porto Alegre, Sociedade Brasileira de Zoonozes. CorneU, W.D., Higgins, K., Abid, H.N., 1988. Dirofilaria immitis infection in cats. Companion Animal Practice 2, 23-25. Courtney, C.H., Zeng, Q.Y., 1987. Predicting heartworm burdens with a heartworm antigen test kit. JAAHA 23, 387-390. Dillon, R., 1984. Feline dirofilariasis. Vet. Clin. North Am.: Small An. Prac. 14, 1185-1199. Dillon, R., 1986. Feline heartworm disease. In: G.F. Otto (Ed.), Proceedings of the Heartworm Symposium '86, New Orleans, LA. American Heartworm Society, Batavia, IL, 149-154. Doi, K., Fujinami, F., Yasoshima, A., Okawa, H., Okaniwa, A., 1982. Lesions in pulmonary artery in feline dirofilariasis. Jpn. J. Vet. Sci. 44, 23-29. Donahoe, J.M.R., 1975. Experimental infection of cats with Dirofilaria immitis. J. Parasitol. 61,599-605. Genchi, C., Guerrero, J., DiSacco, B., Formaggini, L., 1992. Prevalence of Dirofilaria immitis infection in Italian cats. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '92, Austin, TX. American Heartworm Society, Batavia, IL, 97-102. Guerrero, J., McCall, J.W., Dzimianski, M.T., McTier, T.L., Holmes, R.A., Newcomb, K.M., 1992. Prevalence of Dirofilaria immitis infection in cats from the southeastern United States. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '92, Austin, TX. American Heartworm Society, Batavia, IL, 91-95. Guerrero, J., Genchi, C., Vezzoni, A., Ducos de Lahitte, J., Bussieras, J., Rojo, F.A., Ortega, LM., Rodenas, A., Bulman, G.M., Larson, M.H., Labarthe, N.V., Charles, T., Bordin, E.L., 1989. Distribution of
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Dirofilaria immitis in selected areas of Europe and South America. In: Otto, G.F. (Ed.), Proceedings of the Heartworm Symposium '89, Charleston, SC. American Heartworm Society, Batavia, IL, 13-18. Holmes, R.A., Clark, J.N., Cases, H.W., Henk, W., Plue, R.E., 1992. Histopatbologic and radiographic studies of the development of heartworm pulmonary vascular disease in experimentally infected cats. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '92, Austin, TX. American Heartworm Society, Batavia, IL, 81-89. Horioka, E. et al., 1984. A feline case of Dirofilaria immitis infection. J. Jap. Vet. Med. Assoc. 37, 451-455. Knight, D.H., 1987. Heartworm infection. Vet. Clin. North Am.: Small Ani. Prac. 17, 1463-1518. Labarthe, N.V., Almosny, N.R., Soares, A.M., Souza-Silva, L.C., 1992. Update on the Distribution of Dirofilaria immitis in the State of Rio de Janeiro, Brazil. Proceedings of the XVII WSAVA World Congress, Italy, 291-293. Labarthe, N.V., Pereira, N.R., Soares, A.M., Bordin, E., Rotta, A., 1990. Dirofilariose canina no estado do Rio de Janeiro: preval~ncia das formas oculta e microfilar~mica. An. XII Cong. Bras. Clin. Vet. Peq. An., Gramado, 16. Lewis, R.E., 1986. Radiographic findings in feline dirofilariasis. In: Otto, G.F. (Ed.), Proceedings of the Heartworm Symposium '86, New Orleans, LA. American Heartworm Society, Batavia, IL, 155-158. Mansour, A.E., McCall, J.W., McTier, T.L., Supakorndej, N., Ricketts, R., 1995. Epidemiology of feline heartworm infection: laboratory studies on transmission and on host preference of mosquito vectors. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium "95, Auburn, AL. The American Heartworm Society, Batavia, IL, 87-95. McCall, J.W., Calvert, C.A., Rawlings, C.A., 1994. Heartworm infection in cats: a life-threatening disease. Vet. Med. 89, 639-647. McCall, J.W., Dzimianski, M.T., McTier, T.L., Jernigan, A.D., Jun, J.J., Mansour, A.E., Supakorndej, N., Plue, R.E., Clark, J.N., Wallace, D.H., Lewis, R.E., 1992. Biology of experimental heartworm infection in cats. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '92, Austin, TX. American Heartworm Society, Batavia, IL, 71-79. McCall, J.W., Supakorndej, N., Ryan, W., Soil, M.D., 1995. Utility of an ELISA-based antibody test for detection of heartworm infection in cats. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '95, Auburn, AL. American Heartworm Society, Batavia, IL, 127-133. Newton, W.L., Wright, W.H., 1956. The occurrence of a dog filariid other than Dirofilaria immitis in the United States. J. Parasitol. 42, 246-256. Nunes, A., 1992. A incid~ncia de D. immitis em gatos em Ubatuba - SP. In: An. XV Cong. Bras. Clin. Med. Vet. Peq. Animais, Rio de Janeiro, RJ, ANCLIVEPA, 52. Otto, G.F., 1974. Occurrence of the heartworm in unusual locations and in unusual hosts. In: Morgan, H.C. (Ed.), Proceedings of the Heartworm Symposium '74, Bonner Springs, KS. VM Publishing, 6-13. Rawlings, C.A., 1986. Heartworm Disease in Dogs and Cats. Saunders, Philadelphia, PA, 104-114. Rawlings, C.A., Farrel, R.L., Mahood, R.M., 1990. Morphologic changes in the lungs of cats experimentally infected with Dirofilaria immitis. J. Vet. Intern. Med. 4, 292-303. Riley, W.A., 1922. Dirofilaria immitis in the heart of a cat. J. Parasitol. 9, 48. Ryan, W.G., Newcomb, K.M., 1995. Prevalence of feline heartworm disease - - a global review. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '95, Auburn, AL. The American Heartworrn Society, Batavia, IL, 79-86. Travassos, L., 1921. Notas helmintol6gicas. Brazil Med. 2, 67.
Veterinary Parasitology 71 (1997) 301 -306
Survey of Dirofilaria immitis (Leidy, 1856) in random source cats in metropolitan Rio de Janeiro, Brazil, with descriptions of lesions Norma Labarthe a,,, Ana Maria Reis Ferreira b Jorge Guerrero c Kathleen N e w c o m b c, Elan Paes-de-Almeida b a Faculdade de Veterinfria, Universidade Federal Fluminense, Rua Vital Brazil Filho 64, 24230-340, Niterf~i, Rio de Janeiro, Brazil b Departamento de Patologia, Unil~ersidade Federal Fluminense, Rua Marquez do Paran6, 300 Niter6i. Rio de Janeiro, Brazil c Merck and Co, Inc., P.O. Box 2000, Rahway, NJ, 07065-0912, USA
Received 13 January 1997; accepted 25 February 1997
Abstract To evaluate the prevalence of heartworm disease in metropolitan Rio de Janeiro, RJ, Brazil, cats submitted for euthanasia were evaluated by laboratory tests and by necropsy for signs of heartworm infection. Of the 125 cats examined, one (0.8%) - - a stray male from an urbanizing district - - had one male worm (14.5 cm) in the left lung and showed severe muscular hypertrophy of small pulmonary arteries and arterioles with no right ventricle enlargement or passive congestion. Microfilariae were not detected in the blood of any cats. The prevalence of canine heartworm in the area from which this cat originated is estimated to be approximately 12%. The prevalence of canine heartworm in the urban area of Rio de Janeiro has been determined to be approximately 5%. It has been shown that the prevalence of feline heartworm disease parallels that in dogs, but at a lower rate. Results of this survey strongly suggest that heartworm prevention measures should be taken under consideration, especially among cats living in a high canine heartworm prevalence area. © 1997 Published by Elsevier Science B.V. Keywords: Dirofilaria immitis; Heartworm; Cat; Feline
* Corresponding author. Gustavo Sampaio 194/1101, Leme, 22010-000, Rio de Janeiro, RJ-Brazil. Fax: +55 21 2952052. 0304-4017/97/$17.00 © 1997 Published by Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 4 0 1 7 ( 9 7 ) 0 0 0 4 1 - 1
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N. Labarthe et al. / Veterinary Parasitology 71 (1997) 301-306
1. Introduction Once believed to be a rare parasite of cats, Dirofilaria immitis is diagnosed with greater frequency today. Although cats are not considered normal hosts of D. immitis, they are indeed susceptible to heartworm infection and it is recognized that it is likely to be a life-threatening disease in cats (Donahoe, 1975; McCall et al., 1994; Mansour et al., 1995). The perception of increased prevalence of feline heartworm disease could be either due to better diagnostic skills and awareness of veterinarians, or because more cats are becoming infected by D. immitis (Guerrero et al., 1992). Although diagnostic tests are improving, feline heartworm is still difficult to detect and estimates of the prevalence are likely to be inaccurate (Rawlings, 1986). The majority of infected cats are amicrofilaremic and low worm burdens are also characteristic of feline heartworm infections, which make it difficult for detection using microfilarial or ELISA antigen tests (Courtney and Zeng, 1987; Guerrero et al., 1992). An ELISA antibody test has been considered helpful in the diagnosis of heartworm infections in feline patients, but the reliability of this test is still being investigated (McCall et al., 1995). One of the most important antemorten diagnostic procedures in the cat is the radiographic examination of the thorax. The detection of enlarged lobar arteries suggests a positive heartworm diagnosis (Lewis, 1986). Feline heartworm prevalence generally parallels that in dogs at a given location, but at a lower rate (Otto, 1974; Dillon, 1984). The first report of feline heartworm infection seems to have been from Brazil (Travassos, 1921), followed by a second report in 1922 from USA (Riley, 1922). Recently, several reports from around the world have been documented in two reviews (Dillon, 1986; Ryan and Newcomb, 1995). Since the initial report in 1921, little information has been published on feline heartworm infections in Brazil. In Rio de Janeiro City, Chagas et al. (1989) reported a worm found in a cat during necropsy and in S5o Paulo state, Nunes (1992) reported 12 infected animals out of 24 cats examined in a heavily enzootic canine heartworm area. Eleven of these 12 cats were diagnosed by ELISA antigen tests and one case was discovered by necropsy. In Rio de Janeiro, the prevalence of canine heartworm is estimated to range from 16 to 21% (Guerrero et al., 1989; Labarthe et al., 1990). When the area is split into sections according to the urbanization pattern, the urban area shows a prevalence of nearly 5%, urbanizing districts show 12%, and the rate in suburbs is around 33% (Labarthe et al., 1992). The present survey was initiated to update data on feline heartworm in Rio de Janeiro City.
2. Materials and methods 2.1. Experimental animals
From April 1993 to April 1994, 125 adult cats, including 87 females and 38 males from the metropolitan Rio de Janeiro, RJ, Brazil, were selected at random from those scheduled for euthanasia. Each animal was uniquely identified, and all available information on the animal was recorded. Animals were handled considering their
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303
welfare throughout the trial procedures. The districts from which cats originated were classified according to the urbanization pattern as either urban or in the process of becoming urbanized. 2.2. Blood sample collection and testing From each cat, a blood sample was drawn in a tube containing EDTA. After collection of blood, each animal was given 10000 IU heparin by intravenous injection. Blood samples were examined by a modified Knott test (Newton and Wright, 1956) to detect microfilariae. 2.3. Necropsy examinations Approximately 3 min after the injection of heparin, an intravenous injection of euthanasia solution was administered to the cat. Necropsies were performed at Faculdade de Veterinfiria, Universidade Federal Fluminense. During necropsy, the pleural and peritoneal cavities were examined for the presence of D. immitis, then the lungs and heart were removed, dissected and thoroughly examined. All worms found were removed, identified by sex, measured, enumerated and stored in acetic 10% formalin solution.
3. Results All cats evaluated were amicrofilaremic. At necropsy, one of the 125 cats examined (0.8%) had live D. immitis adult worms. The infected cat was a male stray from an
Fig. 1. Muscular hypertrophy and hyperplasia of the branch of the caudal pulmonary artery with villous projection of the intima and partial obstruction of the arterial lumen. (HE, 100X negative).
304
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urbanizing district, and was thin, weak and very dirty when presented for euthanasia. When data were evaluated by sex, the prevalence was 0% (0/87) in female cats and 2.6% (1/38) in males. According to the type of environment the cat had originated from, prevalence was 0% (0/62) for the urban area and 1.6% (1/63) in the urbanizing districts. The worm recovered from this cat was a mature live male, measuring 14.5 cm in length and was located at the apical region of the cranial portion of the left lung lobe. Both lungs were grossly congested. Histopathological findings included rows of villous projections of the intima into the lumen, diffuse thickening of the subintima and myointimal proliferation with muscular hypertrophy and hyperplasia of the branches of the caudal pulmonary arteries, producing partial obstruction of the arterial lumen (Fig. 1). Other microscopic changes observed were congestion, edema and a discrete adventitial and perivascular inflammatory infiltration of polymorphonuclear and mononuclear cells.
4. Discussion The presence of one adult worm in the apical region of the cranial portion of the left lung, and the severity and distribution of the arterial lesions found in this cat, suggest that the lesions could have been produced by migration of the live worm through the vessels, as has been previously observed (Doi et al., 1982; Horioka et al., 1984; Comell et al., 1988; McCall et al., 1994). Embolic dead adult D. i m m i t i s in the pulmonary artery, characterized by thrombus formation, organization and intimal granuloma that are frequently observed in dogs and cats (Doi et al., 1982; Knight, 1987; McCall et al., 1994 and Calvert et al., 1994), were not observed in the infected cat in this survey. Embolization is a cause of sudden death in infected cats and may be accompanied by severe acute pulmonary hypertension (Knight, 1987). The muscular hypertrophy of small pulmonary arteries and arterioles observed in this cat has also been observed in some normal cats, but is a consistent finding in cats infected with heartworms (Rawlings et al., 1990; McCall et al., 1994 and Calvert et al., 1994). Compensatory hypertrophy and enlargement of the right ventricle and the subsequent systemic passive congestion are familiar findings in canine dirofilariasis and are uncommon developments in cats (Knight, 1987; Doi et al., 1982). They were not evident in this feline case, most likely because the present infection was limited to a single worm. Therefore, it seems that severe chronic pulmonary hypertension is not a common feature of cats with heartworm disease, probably due to the low number of worms usually harbored by them (Knight, 1987). The heartworm-infected cat of this survey came from the urbanizing area, where canine infections are frequently encountered (12%). This suggests that, as in other countries, infection rates for heartworm in cats tend to parallel those in dogs. This is particularly evident in the urban area, where only 5% of the dogs are reported to be infected (Labarthe et al., 1992), and no feline infections were detected in this survey. It
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has been reported by others that male cats seem to be more often infected with D. immitis than females (McCall et al., 1992 and Donahoe, 1975). Findings in the present survey provide additional evidence that this may be true. Although it is generally accepted that the prevalence in cats parallels that in dogs, but at a lower rate, it is interesting to note that in Rio de Janeiro, where canine heartworm infection ranges from 16 to 21%, heartworm infections were detected in 0.8% of the cats evaluated in the present study, while in northern Italy, the prevalence of canine heartworm infection averages around 40%, and in a survey conducted by Genchi et al. (1992), 12.5% of 120 household and stray cats in the area were infected with heartworm. It is conceivable that either cats or worms, or possibly both, have genetic differences to create such a disparity between the two countries, or there may be some correlation with the mosquito vectors, as suggested by Genchi et al. (1992) and Holmes et al. (1992). In any case, the present survey provides further evidence that feline heartworm disease should be given serious consideration in areas known to have a high prevalence of canine heartworm.
Acknowledgements The authors acknowledge Prof. Sebasti~o Jos6 de Oliveira and Prof. Ricardo Louren~o de Oliveira for their support and criticism of the manuscript.
References Calvert, C.A., Rawlings, C.A., McCall, J.W., 1994. Feline heartworm disease. In: Sherding, R.G. (Ed.), The Cat Disease and Clinical Management, 2 "d edn., Vol. 1. Churchill Livingstone, New York, 623-645. Chagas, W.A., Courtino, V., Pimenta, A.L.P., Ribeiro, V.L.S., D'Almeida, S.R.M.J., 1989. OcorrSncia de dirofilariose em Felis cati. In: Anais do I Congresso Internacional de Zoonoses, Porto Alegre, Sociedade Brasileira de Zoonozes. CorneU, W.D., Higgins, K., Abid, H.N., 1988. Dirofilaria immitis infection in cats. Companion Animal Practice 2, 23-25. Courtney, C.H., Zeng, Q.Y., 1987. Predicting heartworm burdens with a heartworm antigen test kit. JAAHA 23, 387-390. Dillon, R., 1984. Feline dirofilariasis. Vet. Clin. North Am.: Small An. Prac. 14, 1185-1199. Dillon, R., 1986. Feline heartworm disease. In: G.F. Otto (Ed.), Proceedings of the Heartworm Symposium '86, New Orleans, LA. American Heartworm Society, Batavia, IL, 149-154. Doi, K., Fujinami, F., Yasoshima, A., Okawa, H., Okaniwa, A., 1982. Lesions in pulmonary artery in feline dirofilariasis. Jpn. J. Vet. Sci. 44, 23-29. Donahoe, J.M.R., 1975. Experimental infection of cats with Dirofilaria immitis. J. Parasitol. 61,599-605. Genchi, C., Guerrero, J., DiSacco, B., Formaggini, L., 1992. Prevalence of Dirofilaria immitis infection in Italian cats. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '92, Austin, TX. American Heartworm Society, Batavia, IL, 97-102. Guerrero, J., McCall, J.W., Dzimianski, M.T., McTier, T.L., Holmes, R.A., Newcomb, K.M., 1992. Prevalence of Dirofilaria immitis infection in cats from the southeastern United States. In: Soil, M.D. (Ed.), Proceedings of the Heartworm Symposium '92, Austin, TX. American Heartworm Society, Batavia, IL, 91-95. Guerrero, J., Genchi, C., Vezzoni, A., Ducos de Lahitte, J., Bussieras, J., Rojo, F.A., Ortega, LM., Rodenas, A., Bulman, G.M., Larson, M.H., Labarthe, N.V., Charles, T., Bordin, E.L., 1989. Distribution of
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