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The Circumoval Precipitin (COP) Test in Schistosomiasis Japonica^*

The COP test with lyophilized Schistosoma japonicum eggs for the laboratory diagnosis of schistosomiasis japonica has been in use in the Department of Parasitology, Institute of Hygiene, University of the Philippines, since 1961. These eggs are isolated from the liver of experimentally infected rabbits.

The employment of lyophilized eggs makes the test practicable for routine use, solving the problem of availability of antigen on a day-to-day basis and simplifying the preparation of the test. Lyophilized eggs stored for as long as 36 months remain highly reactive. Human sera stored for as much as 4 years at -20°C and thawed and refrozen several times remain positive.

An evaluation of the test was conducted with the use of 203 specimens of serum from persons with confirmed schistosomiasis japonica, and 62 specimens from "normal" persons. In addition, a small number of human and animal sera representing various other types of helminthiasis were tested. Results were recorded on the basis of the strongest reaction seen in any one egg in the entire preparation. Septate precipitates were categorized according to their length in comparison with the length and width of S. japonicum eggs. Bleb precipitates were also classed according to their apparent area in comparison with the area of the egg.

By designating as positive only those sera producing septate precipitate, we found the COP test with lyophilized eggs to have an over-all sensitivity of 95% and high species-specificity. The test is less sensitive in older infected persons, especially females; hence, care must be taken in the interpretation of negative tests in such subjects.

^* These investigations were conducted under the sponsorship of the Commission on Parasitic Diseases of the Armed Forces Epidemiological Board and supported by the U.S. Army Medical Research and Development Command, Department of the Army, by contract DA-49-193-MD-2320, and by National Institutes of Health grant, List No. RF-9-61, Allotment No. 1001-03, by arrangements with and support of the authorities of the University of the Philippines, Quezon City, Philippines. A preliminary report on this material was made to the Eleventh Pacific Science Congress, Tokyo, 1966.