Intradermal tests with an acid soluble protein fraction of Paragonimus westermani adults were performed on over 3,000 people. All those with proved infections gave positive dermal reactions. In most cases, it was possible to differentiate between paragonimiasis and clonorchiasis since the area of the wheal resulting from the homologous antigen was usually considerably larger than that resulting from the heterologous antigen. Among patients with proved double infections, the dermal reaction to the Paragonimus antigen was greater.
Information on the epidemiology of paragonimiasis came chiefly from surveys conducted in two provinces. The prevalence rates for different localities were related to the presence and availability of infected crabs and crayfish. In all age groups and all localities more males than females were found to be infected. An increase in prevalence of infection up to adulthood and a decrease afterwards were observed. In approximately 40 per cent of the positive dermal reactors, eggs could be recovered by a single sputum examination. A possible correlation between the intensity of infection and the mean area of the wheals was observed.
The highest percentage of asymptomatic individuals was in the younger age groups. The duration of complaints among symptomatic patients varied from 15 days to 20 years, the mean duration of symptoms increasing with age. The character and severity of symptoms depended largely upon the type of infection, i.e., pulmonary, generalized, pleural, renal, testicular, abdominal, or dermal. Radiography and tomography often revealed the location and character of lesions produced by worms in the brain and lungs, and may prove especially useful in differential diagnosis.
Leukocytosis and eosinophilia were present only in the early stages of infection. Serum electrophoresis indicated a significant increase in the proportion of gamma globulin. Numerous examinations were often required for the detection of eggs. In 8 per cent of the patients with extrapulmonary paragonimiasis, eggs were found by examination of specimens other than sputum.
Reactions to intradermal tests with Paragonimus antigen were more frequent among individuals receiving treatment for active tuberculosis than among those of the general population. Staining of sputa for the detection of acid-fast bacilli distorted P. westermani eggs, frequently beyond recognition.
The specific rate for all kinds of extrapulmonary lesions and the frequency of dermal reactors both showed a peak in the age group 25 to 35 years. This was taken as an indication that in this age group both the highest prevalence and intensity of infection are to be found.
Chloroquine was given by various routes to 116 patients with pulmonary and extrapulmonary paragonimiasis, and resulted in negative sputum and stool examinations for at least 6 months in only 12.5 per cent of the cases. The percentage of apparent cures among patients with a history of disease for less than 2 years was almost 3 times as great as that of those with symptoms of 5 years' duration or longer. Decreased dermal sensitivity to P. westermani antigen was observed in patients who had responded to treatment. Experience has shown that surgery often may be beneficial, and in some cases is the only available means of therapy.
Department of Medical Zoology, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D. C.
Department of Epidemiology, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland.