Estudo retrospectivo (1998 a 2001) da erliquiose canina em Belo Horizonte

abmvz Arquivo Brasileiro de Medicina Veterinária e Zootecnia Arq. Bras. Med. Vet. Zootec. 0102-0935 1678-4162 Universidade Federal de Minas Gerais, Escola de Veterinária Belo Horizonte, MG, Brazil O presente trabalho descreve um estudo retrospectivo da casuística clínica de erliquiose em cães atendidos entre março de 1998 e setembro de 2001. Foram analisadas 194 fichas clínicas de animais com suspeita de hemoparasitoses, nas quais 31 cães foram diagnosticados com Ehrlichia canis e 21 com Ehrlichia platys, por meio de exame parasitológico direto de esfregaços sangüíneos. Foram considerados alguns aspectos demográficos (idade, raça, sexo, época do ano e região de origem), características clínicas (temperatura corporal, presença e/ou histórico de carrapatos e sinais clínicos) e hematológicas (hemograma completo e célula parasitada). O número de diagnósticos de erliquiose aumentou consideravelmente a partir de 2000, sendo que 24,4% dos casos ocorreram em animais entre 13 e 24 meses de idade na cidade de Belo Horizonte e áreas peri-urbanas, verificando-se maior risco de infecção em animais que residiam em casas. Os sintomas mais freqüentes foram febre, anorexia, apatia, dor abdominal, linfadenopatia e dispnéia. Quanto às alterações hematológicas, 70,3% apresentaram anemia, 50% trombocitopenia e 30% leucopenia e a maioria das infecções por E. canis foi visualizada em monócitos. Os resultados apontam para a necessidade de maior atenção por parte dos clínicos e técnicos para a erliquiose canina uma vez que 35,9% dos cães atendidos com suspeita de hemoparasitoses apresentavam infecções por E. canis ou E. platys. Retrospective study (1998-2001) on canine ehrlichiosis in Belo Horizonte, MG, Brazil Estudo retrospectivo (1998 a 2001) da erliquiose canina em Belo Horizonte S.M. Moreira; C.V. Bastos; R.B. Araújo; M. Santos; L.M.F. Passos* Escola de Veterinária da UFMG Caixa Postal 567 30123-970 - Belo Horizonte, MG ABSTRACT The present work describes a retrospective study of clinical cases of ehrlichiosis in dogs examined from March 1998 to September 2001. From the clinical records with laboratorial confirmation of Ehrlichia canis or E. platys infections, the following parameters were analyzed: demographic aspects (age, race, sex, period of the year and origin), clinical characteristics (body temperature, exposure to ticks and clinical signs), and hematological characteristics (blood cell counts and type of infected cell). A total of 194 clinical records were analyzed, from which 31 animals were infected with E. canis and 21 animals with E. platys. The number of cases of canine ehrlichiosis increased considerably from the year 2000 onwards, and 24.4% of the cases occurred in 13- to 24-month-old animals, in different urban and per-urban regions of the municipality of Belo Horizonte. The most frequent symptoms were fever, anorexia, apathy, abdominal pain, lymphadenopathy and dispnea. Regarding hematological alterations, 70.3% of the animals presented anemia, 50% presented thrombocytopenia and 30% leukopenia, and most E. canis morulae were seen in monocytes. The results point to the importance of canine ehrlichiosis, as 35.9% of the dogs with suspected hemoparasitic diseases were infected with Ehrlichia canis or E. platys. Keywords: dog, Ehrlichia canis, Ehrlichia platys, epidemiology RESUMO O presente trabalho descreve um estudo retrospectivo da casuística clínica de erliquiose em cães atendidos entre março de 1998 e setembro de 2001. Foram analisadas 194 fichas clínicas de animais com suspeita de hemoparasitoses, nas quais 31 cães foram diagnosticados com Ehrlichia canis e 21 com Ehrlichia platys, por meio de exame parasitológico direto de esfregaços sangüíneos. Foram considerados alguns aspectos demográficos (idade, raça, sexo, época do ano e região de origem), características clínicas (temperatura corporal, presença e/ou histórico de carrapatos e sinais clínicos) e hematológicas (hemograma completo e célula parasitada). O número de diagnósticos de erliquiose aumentou consideravelmente a partir de 2000, sendo que 24,4% dos casos ocorreram em animais entre 13 e 24 meses de idade na cidade de Belo Horizonte e áreas peri-urbanas, verificando-se maior risco de infecção em animais que residiam em casas. Os sintomas mais freqüentes foram febre, anorexia, apatia, dor abdominal, linfadenopatia e dispnéia. Quanto às alterações hematológicas, 70,3% apresentaram anemia, 50% trombocitopenia e 30% leucopenia e a maioria das infecções por E. canis foi visualizada em monócitos. Os resultados apontam para a necessidade de maior atenção por parte dos clínicos e técnicos para a erliquiose canina uma vez que 35,9% dos cães atendidos com suspeita de hemoparasitoses apresentavam infecções por E. canis ou E. platys. Palavras-chave: cão, Ehrlichia canis, Ehrlichia platys, epidemiologia INTRODUCTION Among the diseases affecting dogs, ehrlichiosis is nowadays one of the most important infections (Woody, Hoskins, 1991). The disease occurs worldwide, particularly in tropical and subtropical areas, associated to infestations of Rhipicephalus sanguineus ticks, its main biological vector (Groves et al., 1975). Ehrlichia canis, first described by Donatien and Lestoquard (1935), is a rickettsia that has been frequently involved in more severe clinical cases, resulting high morbidity and variable mortality (Hoskins et al., 1983). In Brazil the disease was first diagnosed in Belo Horizonte –MG by Costa et al. (1973), who identified inclusions (morulae) in lymphocytes of a naturally infected dog. Infected leukocytes showing E. canis inclusions are usually seen in dogs undergoing ehrlichiosis (Greene, Harvey, 1990). Another species diagnosed in dogs, E. platys, described by Harvey et al. (1978), presents an ultra-structure similar to E. canis and infects preferentially circulating thrombocytes (French, Harvey, 1983). The first clinical manifestations occur after an incubation period of 8 to 20 days, with three distinct stages of infection: acute, sub-clinic and chronic. During the acute phase the organisms multiply inside mononuclear cells, spreading to the liver, spleen and lymphonodes (Woody, Hoskins, 1991). This phase is characterized by fever, weight losses, depression, dispnea (Codner et al., 1985), ocular involvement (Troy, Forrester, 1990), as well as neurological (Meinkoth et al., 1989) and renal alterations (Codner, Maslin, 1992). During the sub-clinical phase, particularly in enzootic regions, some clinically normal animals present laboratory alterations such as cytopenia and hyperglobulinemia for several years (Codner et al., 1985). During the chronic phase the parasite persists intracellularly and the dogs develop pancytopenia and other immunologically mediated manifestations (Codner et al., 1985), with frequent secondary infections that can lead to death. The diagnosis is usually based on detection of morulae inside leukocytes in blood smears. However, the morulae are visualized only during the acute phase and the percentage of infected cells is usually less than 1% (Cadman et al., 1994). Thus, an absence of parasites in blood smears does not exclude the possibility of infection (Hoskins, 1991). Over the last decades the importance of canine ehrlichiosis has increased as a public health problem in the United States. E. chaffeensis, the etiological agent of human ehrlichiosis, presents 98.2% homology with E. canis rDNA (16S) (Anderson et al., 1991) and the two species share the major antigenic proteins (Chen et al., 1994). Human ehrlichiosis has been considered a disease of zoonotic importance by the Pan-American Health Organization (Benenson, 1992) and the advances on the characterization of the canine agent will contribute directly to the studies of human ehrlichiosis. Although the importance of ehrlichiosis has increased, little is known about its clinical and epidemiological aspects in Brazil. Therefore, the present study had the objective of evaluating the occurrence and some epidemiological parameters of clinical cases of ehrlichial infections in dogs examined from March 1998 to September 2001. MATERIALS AND METHODS The study was based on the spontaneous demand of the veterinary hospital of the Veterinary School - UFMG, in Belo Horizonte, from March 1998 to September 2001, taking into account clinical records of dogs with clinical suspicious hemoparasites, from which records with laboratorial confirmation of E. canis and/or E. platys were selected. The laboratorial diagnosis was carried out, when required by the clinician, by direct examination of Giemsa-stained blood smears. For positive animals the following information were analyzed: demographic parameters (age, breeding, sex, period of the year and origin), clinical manifestations (concomitant infections, body temperature, presence of ticks, symptoms), and hematological alterations (type of infected cell, red and white cell counts and platelet counts). RESULTS AND DISCUSSION From a total of 194 records from dogs with suspicious cases of hemoparasites at the veterinary hospital, 145 cases were confirmed by venous blood smear examination. It is important to highlight that detection of E. canis morulae is more efficient in peripheral blood (collected from small capillaries in the ear) than in venous blood smears (Castro, 1997). From all dogs with hemoparasites, 52 were infected with Ehrlichia spp (35.9%), from which 31 were infected with E. canis and 21 with E. platys. Considering the limitations of the direct examination for detection of E. canis (McBride et al., 1996), these figures suggest that a higher percentage of dogs are infected. The number of infected dogs increased considerable from the year 2000 onwards (Fig. 1), possibly due to a higher accuracy of the diagnosis over the last years. Five animals, representing 10% of the dogs with ehrlichiosis, had other associated hemoparasites (Haemobartonella canis and Babesia canis). According to Kordick et al. (1999), co-infections with multiple organisms determine more severe symptoms than single infections. Simultaneous infections are expected in dogs since most hemoparasites are transmitted by the same vector. As far as age and sex are concerned, 24.4% of the animals with ehrlichial infections were from 13 to 24 months old and 61.5% were females. These results can be related to the age in which the reproductive life of males and females starts. At this age a high number of females is brought to the hospital with obstetric disturbances or for castration. Regarding susceptibility between different breeds, 23.1% of the animals belonged to the category ‘undefined breed' (UB). This is probably due to the fact that the majority of dogs examined comprises undefined breed dogs (Assis et al., 1996 cited by Alves, 1996). A wide variety of dog breeds was infected and a high number of dogs (25) were big in size, explaining the fact that 78% of them were living in houses while only 21.9% were living in apartments. This result suggests a higher risk of infection in dogs living in houses. In addition to the housing conditions, an important aspect observed during clinical examination was the exposure to ticks (Table 1). Regarding precedence, the infected animals originated from regions surrounding the Veterinary Hospital (Pampulha region) and from per-urban areas. High frequency of tick-borne diseases is expected in peri-urban areas, where dogs are in general more exposed to arthropod vectors. Regarding E. platys-infected animals, only direct examination and hematological parameters were evaluated, as epidemiological and clinical data were not available. The most common clinical symptoms observed in dogs with E. canis infections are presented in Fig. 2 and are similar to those described by Ewing (1969). All E. canis infected animals presented fever (39.7ºC). Lymphadenopathy was seen in 27% of the dogs, involving particularly the sub-mandibular and popliteo lymphonodes. Similar percentage has been reported by Kuhen and Gaunt (1985), although Hoskins (1991) reported that lymphadenopathy is an inconstant alteration in cases of ehrlichiosis. Among all infected animals, only one presented splenomegalia. Kuhen and Gaunt (1985) considered splenomegalia a rare alteration, whereas Ewing (1969) reported it as common finding with spleen enlarging up to two or three times its normal size. In addition, hepatomegalia, also observed in two animals, indicates severe disease, involving acidophylic hepatocyte degeneration or necrosis. Hildebrandt et al. (1973) reported that the most common lesions are seen inside the thoracic cavity and that pulmonary alterations are present in 70% of dogs with acute ehrlichiosis. In the present study dispnea was the most common alteration seen (26.9%) in dogs with respiratory manifestations. Pneumonia was observed in one dog. Thickness of alveolar septum with pronounced interstitial reaction has been described as one of the most important lesions in infected animals (Reardon, Pierce, 1981). Epistaxe was observed in 15.4% of the dogs with hemorrhagic disturbance. This alteration is common during the chronic phase of infection, due to hemorrhagy in the lungs or on the nasal mucosa, and may be present in 30 to 50% of the severe cases, with petechia in the abdomen, genital and conjunctival mucosa, conjunctiva, and inside the oral cavity (Eng, Giles, 1989). Two dogs presented petechia, one in the abdomen and oral cavity, and another in the prepucial region. Alterations in the nervous system were observed in 19.2% of the animals infected with E. canis. Ataxia, paresia and paralysis have been described in experimental infections and may occur either during the acute or chronic phases due to mononuclear cell infiltration or hemorrhagy on the meninge (Greene, 1985), which are common alterations (Valli, 1993). The same frequency (19.2%) was observed for locomotors difficulties. Among the infected animals, 50% showed join edema. This symptom is associated to chronic phases, when the animals may also present lack of coordination and generalized edema (Meinkoth et al., 1989). Edema has been reported in 33% of infected animals (Greene et al., 1985) and poliarthritis has been frequently associated to E. ewingii infections (Stockham et al., 1985). Complete hemograms were examined for 50 animals with characteristic inclusions (morulae) of either E. platys inside thrombocytes or E. canis infecting distinct leukocytes (monocytes, lymphocytes and neuthrophils). Dogs can be infected with distinct species of ehrlichias, including some that are traditionally considered primary pathogens of other animals. According to Dawson et al. (1997), more than one species may infect the cell line of a host and some species may infect different cell types. In the present study the rickettsemia was predominantly detected in monocytes (48.4%), which, according to Ewing (1969), are the most commonly infected leukocytes. The most frequent hematological alterations were anemia (70.3%), thrombocytopenia (50%) and leukopenia (30%). According to Greene and Harvey (1990), these alterations occur during the acute phase and usually persist during the sub-clinical phase, and they can persist even during the chronic stages of infection (Woody, Hoskins, 1991). Leukopenia has been reported as one of the most common alterations in infected dogs. The immunological mechanisms responsible for induction of leukopenia are probably the same responsible for development of normocytic-normochromic anemia. It is believed that the erythrocytes are removed from circulation by the monocyte/macrophage system and lysed by the complement (due to an hypersensitivity immunological reaction type II) in addition to suppression of erythropoiesis in the bone marrow. Phagocytosis of antibody-opsonised erythrocytes has been reported by Hoskins (1991) in E. canis infected animals. It is common to have a positive direct Coombs test for these animals, misleading the diagnosis of immuno-mediated hemolytic anemia. Generalized vasculitis has also been reported (Hibbler et al., 1986) in E. canis infections, associated to production of IL-1, which may play an important role in marginalisation and adhesion of leukocytes to the vascular wall and consequently accumulation of cells in inflammation foci (Cotran et al., 1989). Increased number of bastonets was seen in 66.7% of the positive animals, in addition to significant decrease of eosinophils in 43.3% of the cases and monocytopenia in 30% of the dogs. Waddle and Littman (1988), also in a retrospective study on 27 natural cases of canine ehrlichiosis, reported neuthropenia, lymphopenia, eosinopenia and monocytopenia in 22%, 48%, 63% and 51% of the animals, respectively. Kuhen and Gaunt (1985) also reported the same alteration in 56 cases of infection, but with lower frequencies. It is important to emphasize that the great majority of the studies, including the present, have been carried out on natural infections, not knowing which phase of infection the animals were undergoing and not considering the influence of stress caused by the parasite on the development of secondary alterations in the leukogram. The clinical and laboratorial findings of the present study point to the need of further and more detailed studies on E. canis Brazilian isolates in an attempt to help clinicians, technicians and researchers to understand canine ehrlichiosis. CONCLUSIONS The number of confirmed cases of canine ehrlichiosis has increased considerably in Belo Horizonte over the last years. Therefore, there is a need for more attention from clinicians and technicians for this disease that represents 35.9% of the suspicious cases of hemoparasites, with higher risk for dogs living in houses. In infected animals, normocytic-normochromic anemia is the most common hematological alteration, rather than thrombocytopenia. Recebido para publicação em 21 de dezembro de 2001 Recebido para publicação, após modificações, em 26 de agosto de 2002 * Autor para correspondência ( corresponding author): E-mail: [e-mail] ALVES, P.A.B. 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