Serologic and intradermal tests for parasitic infections

A cross-sectional study of intestinal parasitic infections in a rural district of west China

BACKGROUND

Parasitic infections are widespread in rural areas of West China. The remote and humid environment, traditional ways of life, contaminated potable water and limited health services all contribute to the transmission and persistence of fecal parasites.

OBJECTIVE

To describe the prevalence of intestinal parasitic infections in an area of West China, including its associations with demographic variables.

METHODS

Single fecal specimens were collected using a previously validated kit. Parasites were detected microscopically by iodine-stained smear, modified Kato-Katz thick smear, simple saline smear, test tube filter paper culture and adhesive cellophane tape anal swab.

RESULTS

The prevalence of enteric parasites in the population was 51.7%. The proportion of individuals infected with one parasite was 36.5%, two parasites 12.7%, three parasites 3.0% and four parasites 0.08%. Parasites identified included Ascaris lumbricoides in 41.4% of all individuals tested, Ancylostoma duodenale in 17.7%, Trichurias trichuria in 8.25%, Enterobius vermicularis in 0.43%, Blastocystis hominis in 1.37%, Entamoeba coli in 0.47%, Entamoeba histolytica in 0.16%, Giardia lamblia in 0.04%, Strongyloides stercoralis in 0.04% and Clonorchis sinensis in 0.04%. The prevalence was significantly increased in women, people aged 15 to 19 years and over 80 years, the rural farm population, farmers, preschool and primary school groups, residents of a hilly rather than mountainous or plains terrain, and in intermediate income groups. The prevalence was significantly negatively associated with educational level, but not with age or income.

CONCLUSIONS

This study supports the use of simple fecal examinations to monitor the parasite burden in rural areas of developing countries. Enteric parasites remain common in this population in rural China.

Development of an immunobinding dot-blot assay as an alternative for the serodiagnosis of human cysticercosis

An immunobinding dot-blot assay (DBA) was developed on nitrocellulose paper for the serodiagnosis of human cysticercosis, using Cysticercus cellulosae as antigen. The DBA had an immunological sensitivity of 0.08 mg of antigen protein/ml; however, it showed cross-reactions with antigens of adult Taenia solium and Echinococcus granulosus, but not with Toxoplasma gondii and Entamoeba histolytica antigens. An enzyme-linked immunosorbent assay (ELISA) was used as the gold standard for obtaining the diagnostic validity of the DBA, giving 84.61%, 100.00%, 100.00% and 97.98% for epidemiological sensitivity, epidemiological specificity and positive and negative predictive values, respectively. There were no statistical differences between the two tests (P < 0.05, kappa = 0.907). This study showed that DBA is an alternative method for the serodiagnosis of human cysticercosis.

The present status of serodiagnosis and seroepidemiology of schistosomiasis

The literature of the past 4-5 yr on serodiagnosis and seroepidemiology of schistosomiasis is reviewed. A variety of assays with different antigens are being used for serodiagnosis. Several purified antigens appear to be sensitive and specific, but have little if any capability of indicating duration of infection, parasite burden, or effect of chemotherapy. The results of long-term posttherapy field studies indicate that serology has a role in monitoring control programs. Standardized serologic assays and the need for International Standard Reference Sera are emphasized. A standardized enzyme-linked immunosorbent assay based on the Falcon Assay Screening Test system (FAST-ELISA), and involving a standard reference serum pool, is suitable for both serodiagnosis and field studies. Measurement of circulating antigens as a parameter of active infection is considered to have increased potential, compared with antibody measurement, in management of clinical disease and in control programs. Recombinant DNA technology may be useful for producing standard antigens for use in assays measuring antibody or circulating antigen. Time-resolved immunofluorescence involving europium-labeled conjugates may provide the increased assay sensitivity needed for measurement of circulating antigen.

Toxoplasmosis

Infection with T. gondii can have devastating effects on the development of the unborn human fetus. As veterinarians or physicians, we should be able to accurately assess the true risk of exposure of a person to meat-borne tissue cysts or to oocysts based on the age, health, roaming and feeding habits of their cats, and the occupational or recreational activities of the individual. When time precludes an in-depth discussion of preventive measures to decrease exposure to the parasite, the whole client education program can be neatly summarized in the admonition, "When pregnant, wash your hands thoroughly before eating or touching your face, and cook your meat thoroughly." In this way, the risk of exposure to toxoplasmosis and all other meat- or soil-borne diseases is greatly reduced.