TOXOPLASMOSIS IN THE MARSHALLISLANDS the Rongelap group: retinochoroiditis has occurred with similar frequency amongthedifferent exposure categories (Table 2). Two Rongelap individuals had retinal findings compatible with Toxoplasma chorioretinitis but no detectable antibody. Since a combination of retinal and serologic evidence is required for a diagnosis of Toxoplasma chorioretinitis,"? their eye lesions presumably have some otheretiology. Severely immunosuppressed persons occasionally develop seronegative toxoplasmosis.' but no clinical features suggest severe immunosuppression in the Rongelap group, nor would it be anticipated from the radiation dose they received. There is no evidence for the introduction of bias into the 1981-1982 findings due to earlier mortality in the exposed groups because survival curves since 1954 are virtually identical to that of the comparison group.’ The proportion surviving in the Rongelap, Utirik. and comparison populations in 1982 was 74%, 70%, and 70%, respectively. No propensity for any type of infection has been documentedas a delayedeffect of radiation exposure in Japanese atomic bombing survivors or the exposed Marshallese.'*'5 Recent evaluation of the exposed Marshallese has revealed serum levels of immunoglobulin and skintest reactivity to tuberculin and Candidin to be similar to the comparison population.'® Nevertheless, seropositivity and antibodytiters to each of 10 infectious agents were lower in the Rongelap group than in the comparison population when tested a few years after exposure.'’ In addition, blood lymphocyte concentrations have generally been about 15% lower in the Rongelap group. Impaired lymphocyte responsiveness to PHA, an increased prevalence of hepatitis B surface antigenemia, and perhaps an increase in cirrhosis associated with hepatitis B have been reported in Japanese exposed to > 100 rads.'*-?° It is therefore prudent not to consider the matter of susceptibility as settled, pending further observations with diagnostic techniques unavailable in earlier post-exposure years. With regard to toxoplasmosis, an infection controlled primarily by cellular immune mechanisms, serum levels of antibody during immunosuppression mayberelatively unimportant.?!:?? Therefore, if the increased prevalence of seronegativity in the more highly exposed Marshallese reflects defective T. gondii antibody induction or production, it may be clinically insignificant. Nevertheless, the numberofpersonsin the high dose group is small. JUEZou 319 Drawing an analogy with the stochastic nature of neoplastic disease following irradiation, a significant increase in incidence of T. gondii reac- tivation conceivably might be detectable in a Jarger population. ACKNOWLEDGMENTS This investigation was supported by the U.S. Departmentof Energy under contract DE-AC0Q276CHO0016. REFERENCES 1. Feldman, H. A., 1982. Epidemiology of toxo- plasmainfections. Epidemiol. Rev., 4: 204-213. 2. Ruskin, J., and Remington, J. S., 1976. Toxoplasmosis in the compromised host. Ann. Int. Med., 84: 193-199. 3. Smith, R. E., and Ganley, J. P., 1972. Ophthalmic survey of a community. I. Abnormalities of the ocular fundus. Am. J. Ophth., 74: 1126-1130. 4. Cronkite, E, P., Bond. V. P., Conard, R. A., Shulman, N. R., Farr, R. S., Cohn. S. H., Dunham, C.L., and Browning, L. E., 1955. Response of human beings accidentally exposedto significant fall-out radiation. J. Am. Med. Assoc., 159: 430434. 5. Wallace, G. D., 1969. Serologic and epidemiologic observations on toxoplasmosis on three Pacific atolls. Am. J. Epidemiol., 90: 103-111. 6. Wallace, G. D., 1976. The prevalence of toxoplasmosis on Pacific islands, and the influence of ethnic group. Am. J. Trop. Med. Hyg., 25: 48-53. 7. Darrell, R. W., Pieper, S., Jr., Kurland, L. T., and Jacobs, L., 1964. Chorioretinopathy and toxo- plasmosis. An epidemiologic study on a South Pacific island. Arch. Ophthalmal., 71: 63-68. 8. Lessard, E., Miltenberger, R., Conard, R., Musolino, S., Naidu, J., Moorthy, A., and Schopfer, C., 1985. Thyroid-absorbed dose for people at Rongelap, Utirik, and Sifo on March 1, 1954. Brookhaven Natl. Lab. Rep. No. 51882. Upton. New York. 9. Adams, W. H., Harper, J. A., Rittmaster, R. S., Heotis, P. M., and Scott, W. A., 1983. Medical status of Marshallese accidentally exposed to 1954 Bravo fallout radiation: January 1980 through December 1982. Brookhaven Nati. Lab. Rep. No. 51761. Upton, New York. 10. Walls, K. W., and Barnhart, E. R., 1978. Titration of humanserum antibodies to Toxoplasma gondii with a simple fluorometric assay. J. Clin. Microbiol., 7: 234-235. 11. Wallace, G. D., Marshall, L., and Marshall, M., 1972. Cats, rats, and toxoplasmosis on a small Pacific island. Am. J. Epidemiol., 95: 475-482. 12. Schlaegel, T. F., Jr., 1976. Toxoplasmosis. Pages 1-17 in T. D. Duane, ed., Clinical Ophthal-