Hirofumi Sakai

A population-based, case-control study of Taenia solium taeniasis and cysticercosis

A two-phase study was conducted in a rural community in Honduras, to evaluate the association between neurocysticercosis (NCC) diagnosed by computed tomography (CT), epilepsy, seropositivity for antibodies to the cysticerci of Taenia solium [determined by enzyme-linked-immunoelectrotransfer-blot (EITB) assays], intestinal infection with this parasite, and various epidemiological factors. Of the 480 individuals studied in the first phase, 17% were seropositive and 2.5% supplied faecal samples which contained T. solium eggs. In the second phase, 148 individuals (74 of the seropositive subjects from the first phase and 74 matched controls from the seronegatives) underwent CT and neurological examinations. The CT results appeared normal in 110 (74%) of the 148, showed anatomical abnormality in seven (5%), and active or calcified lesions compatible with NCC in 31 (23% of the seropositives and 19% of the seronegatives). Only five of the latter had neurological symptoms (two being epileptics) and only five lived in households in which intestinal taeniasis had been detected. Subject age was significantly associated with NCC-compatible lesions but all the other factors investigated, including seropositivity, showed no significant association with the CT findings. The overall sensitivity of the EITB assays was found to be 55%. Taken together, the present results indicate that, even though it is a valuable tool in determining transmission levels in sero-epidemiological studies, the EITB assay should not be used to predict the existence of NCC or to estimate the prevalence of NCC. The results do provide further evidence that taeniasis and cysticercosis are widely prevalent in Honduras, and indicate that much larger studies of hyper-endemic communities may be necessary if the factors associated with the transmission of T. solium are to be elucidated.

Coproantigen detection in dogs experimentally and naturally infected with Echinococcus granulosus by a monoclonal antibody-based enzyme-linked immunosorbent assay

A sandwich ELISA for the detection of Echinococcus granulosus coproantigen in formalin and heat-treated faecal supernatants of dogs was developed. The assay used affinity-purified polyclonal antibodies obtained from rabbits hyperimmunised with E. granulosus excretory/secretory antigens and biotinylated monoclonal antibody EmA9 produced against adult E. multilocularis somatic extract. The test was sensitive to 7 ng and 2.3 ng of E. granulosus protein and carbohydrate/ml of faecal supernatant, respectively. Thirteen helminth-free dogs were infected with different amounts of E. granulosus protoscoleces and the presence of coproantigen was monitored during the prepatent period until day 35 post-infection, when they were necropsied. Faecal antigen levels started to rise above the normal range between days 10 and 20 post-infection, and typically peaked at the end of the experiment. All the dogs, bearing from 3 to 67,700 worms, showed positive values in the ELISA during the prepatent period. One dog experimentally infected with Taenia hydatigena metacestode and harbouring three worms, tested positive only after the prepatent period at day 52. The test was applied to 98 stray dogs. The ELISA detected all of four dogs naturally infected with E. granulosus, two dogs with patent infections of T. hydatigena and two dogs with no cestode infections, showing a sensitivity of 100% and a specificity of 96%.

Potential remedy against Echinococcus multilocularis in wild red foxes using baits with anthelmintic distributed around fox breeding dens in Hokkaido, Japan

The effect of bait-delivered anthelmintic to reduce the prevalence of Echinococcus multilocularis in wild red foxes was evaluated in Koshimizu, in the eastern part of Hokkaido, Japan. The study area (200 km2) was divided into baited and non-baited sections. The anthelmintic baits were distributed around fox den sites in the baited section every month for 13 months. After 1 year of the anthelmintic bait distribution, the prevalence of E. multilocularis in foxes, evaluated either by the parasite egg examination (from 27.1 to 5.6%) or coproantigen ELISA (from 59.6 to 29.7%), decreased in the baited section contrasting to that in the non-baited section (parasite egg: from 18.8 to 24.2%; ELISA: from 41.9 to 45.8%). The prevalence of E. multilocularis in grey red-backed vole Clethrionomys rufocanus, caught around fox dens, born after bait distribution also decreased and was significantly lower than that in non-baited section. However, within the study periods, the coproantigen-positive rate in fox faeces sporadically increased, while egg-positive rate constantly decreased. Since coproantigen ELISA can detect pre-patent infection, this observation indicates that reinfection pressure in the baited section was still high even after the 13 months of anthelmintic bait distribution. Therefore, the bait distribution longer than our study period is required for the efficient control of E. multilocularis in wild red fox population.

Seroprevalence of Taenia solium cysticercosis in pigs in a rural community of Honduras.

Several retrospective studies have shown that human Taenia solium cysticercosis is endemic in Honduras, but very few reports of porcine cysticercosis in rural communities have been published. To determine the local prevalence of this disease in pigs, a serological survey has been undertaken in a rural community, Salamá, in the Department of Olancho in central Honduras. Eighty-five families raising pigs in the community were randomly selected and sera were obtained from pigs older than one month of age. The sera were examined by the enzyme-linked immunoelectrotransfer blot assay (EITB). Of 192 porcine sera, 27.1% (52) were positive by the EITB. Seropositivity did not correlate with age and sex by statistical analysis. With respect to the number and the frequency of recognition of the seven diagnostic glycoprotein bands in the EITB, 67.3% of the positive serum specimens recognized only one band and 80.8% of them recognized GP42-39. Since recognition of GP42-39 has been reported as a characteristic of late infection, these results suggest that most of the seropositive pigs were in the late stage of infection (more than 5-8 weeks postinfection). It seems that pigs in this community may be infected with this parasite soon after the birth and be in a hyperendemic steady state. In view of a high prevalence of antibodies to T. solium in pigs or characteristics of the antigen detected by the EITB, the infection pressure of T. solium appears to be very high in this community. This is probably the case in most of the communities in Honduras.

COPROANTIGEN DETECTION IN A ROUTINE FOX SURVEY OF ECHINOCOCCUS MULTILOCULARIS INFECTION IN HOKKAIDO, JAPAN

Detection of Echinococcus multilocularis coproantigen using sandwich enzyme-linked immunosorbent assay (sELISA) was performed on fecal samples of red foxes. Fecal samples were obtained from the rectum of shot foxes. The antibodies used for sELISA recognize heat-resistant antigens, thus all fecal samples were heated to render it safe for handling before examination. E. multilocularis infection in shot foxes were evaluated by the detection of adult worms in the distal one-sixth portion of the small intestine. Among 103 positive cases out of 430 foxes in a necropsy in 1993, 90 samples were also coproantigen positive (the sensitivity is 87.4%). In 11 out of 13 coproantigen negative cases, less than 10 worms were detected at necropsy. These results suggest that detection of coproantigen is useful for field surveys of foxes naturally infected with E. multilocularis.

Comparison of serodiagnostic tests and ultrasonography for cystic hydatidosis in an epidemiological study of rural Uruguay.

Cystic hydatidosis (CH) caused by Echinococcus granulosus is an important zoonosis worldwide. Several serodiagnostic and ultrasound tests are currently used for screening asymptomatic CH. The sensitivity of the serodiagnostic tests has been demonstrated by several groups to be lower than ultrasonography (US). To explain the mechanism of the difference in sensitivity, a large-scale US survey combined with an IgG4-enzyme-linked immunosorbent assay test was conducted in Uruguay. Our results suggest that certain cyst images, e.g., multivesicular cysts, may be closely associated with a high antibody response regardless of the cyst size, whereas other hydatid lesions, e.g., solid images with/without rolled parasite membranes, have lower antibody responses with a close relationship to cyst size. Seropositivity of subjects who had been treated surgically for removal of hydatid cysts in the last 5 yr was closest to that of actual CH patients, albeit free from CH by US. These findings are important for the proper use of serodiagnostic tests and US for community-based epidemiological studies.

First report of Trichinella nativa in red foxes (Vulpes vulpes schrencki) from Otaru City, Hokkaido, Japan

Forty-three red foxes (Vulpes vulpes schrencki) and nine raccoon dogs (Nyctereutes procyonoides viverrinus) were captured in Otaru City, Hokkaido, Japan and examined by muscle digestion for the presence of Trichinella sp. larvae. Of the foxes, five (11.6%) were positive for larvae of Trichinella nativa while none of the raccoon dogs were found to be positive. This finding suggests that the red foxes are important reservoir hosts of sylvatic trichinellosis in Otaru, Hokkaido. This is the first report on Trichinella nativa in wild red foxes of Hokkaido, Japan.