Cercarial dermatitis in India.

Sir – Human schistosomiasis has not been well documented in India, with a few exceptions (1, 2). Similarly, the public health importance of cercarial dermatitis is under-recognized. Our findings indicate that the condition is widespread and more serious than previously considered. During our work on schistosomiasis in and around Jabalpur, Madhya Pradesh, over the past 30 years, snails have been collected from perennial ponds (originally numbering 52 ponds, but reduced to 5 by urbanization) and low-lying areas, ditches, farmland and roadsides where water and snails collect in the rainy season. Jabalpur has an annual rainfall of 140–160 cm, with a maximum daytime temperature of 42.5 o C; the lower income group of its one million population depends on the ponds and temporary water sources for domestic water supplies, cultivation of water chestnuts, fishing and recreation. The ponds are inhabited by freshwater snails (Vivipara spp., Indoplanorbis exustus, Lymnaea luteola, Helicorbis spp., and Gyrulus spp.). L. luteola was found positive for cercariae of Schistosoma incognitum and Oriento-bilharzia dattai, and I. exustus for those of S. spindale, S. indicum and S. nasale (3). In a recent survey, 2717 L. luteola and 1000 I. exustus snails were collected; of the L. luteola, 0.62%, 2.83% and 0.92% were positive for avian and mammalian schisto-some cercariae and other trematode cercar-iae, respectively, while the corresponding proportions for I. exustus were 0.9%, 0.9% and 4.2%. We made an extensive survey of people who were using the five ponds concerned (Devtal, Gangasagar, Marhai, Medical, and Soopatal). All of them complained about itching and rashes after being in contact with pond water, which they attributed to the mud or Trapa leaves. Intensity of symptoms increased during the rainy season (July– August), longer contact with water, or activities near aquatic vegetation. We found a higher snail concentration near aquatic vegetation, with possible higher cercarial concentration at these sites. The snail population and its positivity increased during the rainy season, which is also the time for planting water chestnuts, hence the people's longer contact with the water and more severe reactions. At the end of the rainy season (September–October), when the fruit is picked without wading in the water, people complained of eruptions and itching on their forearms. When 60 people aged 8–50 years were questioned, it was found that those aged >40 years developed eruptions (mainly in the knee region) within 5–10 minutes of water contact, which persisted for 3–7 days …