Introduction

Dirofilaria sp. (Leidy 1856) causes heartworm in dogs, cats, carnivorous wild animals, equines, not human primates and occasionally human being (Fortes 2004). This parasitism already was found in more than 30 species, being considered by OMS a zoonosis since 1979 (OMS 1979). The adult worm lives in the pulmonary arteries where mature females release first-stage larvae (microfilariae) into the bloodstream. It will be taken up by an arthropod vector (several species of mosquitoes are competent vectors, including Culex pipiens, Aedes albopictus, Anopheles maculipenis and Coquillettidia richiardii), where will occur its development to infective third-stage larvae (L3). These larvae are then inoculated into the final host dermis where, after several months of migration and maturation, reach pulmonary arteries (Simón et al. 2007). At definitive hosts, prepatent period is, at least, six months (Fernandes et al. 1999). The dog and cat usually can be parasitized by D. immitis (heartworm) and D. repens (most commonly described etiologic agents of human infection). Occasional reports exist in the medical literature about Dirofilaria species that affect other animals, including D. tenuis (raccoon worm), D. ursi (bear), D. subdermata (porcupine), D. lutrae (North American otter), D. striata (wild American felines), and D. spectans (Brazilian otter), causing human disease (Nissen & Walker 2006). In wild felids it had been registered in tiger, lion, leopard (Panthera pardus), leopard-misty (Neofelis nebulosa) and leopard-das-snows (Uncia uncia) (Cubas 2006). The illness presents wide distribution, especially in the level of the sea, in tropics and subtropical areas. Occurs frequently in areas infested for mosquitoes, an intermediate obligatory host. Urbanization influence on green areas that serve as fishery for insects has been demonstrated vector's adaptive capacity. Dogs are the main definitive host. In human being, nematode has little possibility to reach adult phase and immature worms are deceased, generally found in isolated pulmonary nodules and erratic places as nervous system (Fraser 1997, Labarthe et al. 1998, Taipe-Lagos & Natal, 2003). In Brazil, as well as in other countries, the tropical or subtropical coastal regions present high canine dirofilariasis prevalence, what does not exclude the possibility to have areas far from the coast where the illness, if presents, becomes a great and frequent problem. Recently, canine heartworm disease has been also diagnosed in Brazilian not-littoral areas (Labarthe 1997; Fernandes et al., 1999). D. immitis prevalence is becoming increasingly recognized in North American wildlife (i.e., coyotes, foxes, wolves, black bears) that may share environments with human activity. This may become increasingly relevant in the future dirofilariasis control, because prophylactic antifilarials can be administered to domestic canines to eradicate and control it in urban areas (Nissen & Walker 2006). The prevalence of D. immitis in coyotes varies from 7% (Missouri, United States) to 75% (Georgia, United States) to 91% (northern California, United States). D. immitis was detected in 14% of red wolves released into the wild in the Alligator River National Wildlife Refuge in North Carolina in the United States, 2-24 months after testing negative for microfilariae during the captive stage. Fifty-six percent of dingoes (Australian wild dog or Canis familiaris dingo) in a tropical region of the Northern Territory, Australia were infected with adult worms of D. immitis (Nissen & Walker 2006). There aren't reports about Dirofilaria occurrence in wild felids kept in captivity at Pará State, Brazil. The present research aim to verify dirofilariasis occurrence in Panthera onca kept in captivity at Pará State, Brazil.

Materials and Methods

Thirteen blood samples were studied. Animals were provenient from "Dr. Adhemar Monteiro Zôo" (Capitão Poço, Pará State, Brazil) and "Segundo Batalhão de Infantaria de Selva "2° BIS"--Batalhão Pedro Teixeira" (Belém, Pará State, Brazil. Animals became food and water restraint before received anesthetic protocol (ketamine and xylazine--10mg/Kg and 1 mg/Kg, respectively). After that blood samples were collected from jugular or cephalic vein, and samples obtained wrapped in tubes containing anticoagulant (EDTA), and immediately transported to Laboratory of Clinic Pathology, kept in refrigerator, until its analysis. Techniques used were "thick drop" and "Modified Knott", developed by Knight (1977) and Newton & Wright (1956), respectively.

Results

In the present research there were six (46%) females and seven (54%) males. From all studied animals, just one (7,7%) was Dirofilaria sp positive. Examination by "thick drop" showed the positive animal, none was positive using "Modified Knott" technique. The positive animal was from Manaus, Amazonas State, Brazil.

Discussion and Conclusions

Researches in dogs from Belém, Pará State, Brazil, conducted by Figueiredo (1995) and Souza et al (1997), showed positivity. Germano et al. (1985) found similar situation at Amazonas, São Paulo, Paraná and Rio Grande do Sul States, Brazil. So, dogs presence associated with environment ideal conditions and mosquitoes presence are factors that can allow the life cycle development. Lower prevalence in the present research can be determined by occult infection using IFA and ELISA tests, similar to that described by Bendas et al. (2007) and Labarthe et al. (1997). Heartworm disease in cats is not as common as it is in dogs, but an increasing number of cases are reported each year. The frequency of heartworm infection in cats in a particular location correlates with that in the dog population but at a lower incidence (Patton & McCracken 1991). Researches developed by Rawlings & Calvert (1998), Figueiredo (1995) and Souza et al. (1997) in dogs showed a greater occurrence in males than females, similar to this research. Stress can be a determinant factor to diseases development, especially in wild animals. So, knowledge about biology and diseases that affect wild animals are important so that illness recognition be as fast as possible. This is the first report of heartworm disease in Panthera onca kept in captivity at Pará State, Brazil. Additional researches are necessary to determine the real occurrence of this disease at Amazon Region.

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