An enzyme-linked immunosorbent assay for antibodies to Hepatozoon canis.

Canine hepatozoonosis is a tick-borne protozoal disease caused in the Old World and South America by Hepatozoon canis. An enzyme-linked immunosorbent assay (ELISA) using purified H. canis gamont antigen was applied for the detection of antibodies reactive with H. canis. Evaluation of the ELISA with sera from naturally infected parasitemic dogs indicated that it was sensitive (86%), specific (97%), and comparable to the indirect fluorescent antibody test (IFAT) for the detection of H. canis antibodies. A variable degree of serologic cross-reactivity was found between sera from H. americanum-infected dogs and the H. canis antigen. Dogs experimentally infected with H. canis seroconverted 1-4 weeks post-infection (PI). Antibody levels peaked at 7-9 weeks PI and gradually declined thereafter remaining above the cut-off value until the conclusion of the study 7 months PI. The ELISA will be valuable for serological evaluation of dogs suspected of exposure to H. canis and for epidemiological studies.

A new Hepatozoon species from dogs: description of the causative agent of canine hepatozoonosis in North America.

A new species of Adeleina, Hepatozoon americanum, is described from the skeletal muscle, cardiac muscle, visceral organs, and blood of dogs (Canis familiaris) in the Southern United States. The organism was previously identified as Hepatozoon canis (James, 1905) Wenyon, 1926; however, differences in clinical signs, histopathological and serological findings, gamont size, and ultrastructure define the new species of Hepatozoon. Attempts to transmit the protozoan from infected dogs to nymphal Rhipicephalus sanguineus ticks, the definitive host of H. canis, were not successful.

Hepatozoonosis in dogs: 22 cases (1989-1994).

OBJECTIVE: To document hepatozoonosis in dogs from Alabama and Georgia and to report associated clinical signs, method of diagnosis, response to treatment, and course of disease. DESIGN: Retrospective case series. ANIMALS: 22 dogs in which Hepatozoon canis was identified by microscopic examination of skeletal muscle. PROCEDURE: We reviewed medical records of all dogs with a definitive diagnosis of hepatozoonosis that were referred to the Auburn University Small Animal Clinic between 1989 and 1994. RESULTS: Diagnoses were confirmed by microscopic identification of H canis schizont or merozoite stages in skeletal muscle. The gametocyte stage was not detected in smears of blood obtained from a peripheral vein, buffy-coat smears, or bone marrow evaluation. Common clinical signs included fever, cachexia, ocular discharge, pain, stiffness, and paresis. Laboratory abnormalities included marked leukocytosis, hypoglycemia, hypoalbuminemia, mild anemia, hyperphosphatemia, and high alkaline phosphatase activity. Periosteal bone proliferation was evident radiographically in 18 of 22 dogs. Renal lesions included amyloidosis (1 dog), interstitial nephritis (3), and mesangioproliferative glomerulonephritis (4). Treatment with the anticoccidial drug toltrazuril, despite an initial favorable response, failed to prevent relapse in all but 3 of 21 treated dogs. Mean survival time was 12.6 +/- 2.2 months, with a mean time of remission before recurrence of clinical signs of 6 months. CLINICAL IMPLICATIONS: H canis infection in dogs can be associated with a distinct clinical syndrome that involves chronic myositis, debilitation, and death. The dogs of this report represent the first substantial number of domestic dogs naturally infected with H canis in the United States outside of the Texas Gulf Coast. Hepatozoon canis appears to be a serious pathogen in the United States that is becoming more widespread geographically.

Treatment of dogs infected with Hepatozoon americanum: 53 cases (1989-1998).

OBJECTIVE: To determine clinical and pathologic findings before and after short-term (group 1) and long-term (group 2) treatment in dogs with Hepatozoon americanum infection. DESIGN: Retrospective study. ANIMALS: 53 dogs with H. americanum infection. PROCEDURE: Medical records of dogs that were treated for hepatozoonosis diagnosed on the basis of meront or merozoite stages in skeletal muscle were reviewed. RESULTS: Circulating gametocytes of H. americanum were identified in 12 of 53 dogs. Dogs were treated with various drugs, including toltrazuril, trimethoprim-sulfadiazine, clindamycin, pyrimethamine, and decoquinate. Mean WBC counts prior to treatment were 85,700 and 75,200 cells/microl in groups 1 and 2, respectively, and 1 month after initiation of treatment were 12,600 and 14,600 cells/microl, respectively. Initial response to treatment was excellent in all dogs. Twenty-three of 26 dogs in group 1 relapsed at least once and died within 2 years; mean (+/- SD) survival time was 12.6+/-2.2 months. Twenty-two of 27 group-2 dogs survived; 11 dogs had no clinical signs and were still receiving decoquinate (mean duration of treatment, 21 months), 11 dogs had no clinical signs after treatment for 14 months (range, 3 to 33 months; mean survival time, 39 months [range, 26 to 53 months]), 2 dogs were lost to follow-up, and 3 dogs were euthanatized because of severe disease. CONCLUSIONS AND CLINICAL RELEVANCE: Although no treatment effectively eliminated the tissue stages of H. americanum, treatment with trimethoprim-sulfadiazine, clindamycin, and pyrimethamine followed by long-term administration of decoquinate resulted in extended survival times and excellent quality of life.

Genetic and antigenic evidence supports the separation of Hepatozoon canis and Hepatozoon americanum at the species level.

Recognition of Hepatozoon canis and Hepatozoon americanum as distinct species was supported by the results of Western immunoblotting of canine anti-H. canis and anti-H. americanum sera against H. canis gamonts. Sequence analysis of 368 bases near the 3' end of the 18S rRNA gene from each species revealed a pairwise difference of 13.59%.