Abstract
Cercariae of bird schistosomes (genus Trichobilharzia) are able to penetrate the skin of mammals (noncompatible hosts), including humans, and cause a Th2-associated inflammatory cutaneous reaction termed cercarial dermatitis. The present study measured the antibody reactivity and antigen specificity of sera obtained after experimental infection of mice and natural infection of humans. Sera from mice re-infected withT. regenti showed a bias towards the development of antigen-specific IgM and IgG1 antibodies and elevated levels of total serum IgE, indicative of a Th2 polarized immune response. We also demonstrate that cercariae are a source of antigens triggering IL-4 release from basophils collected from healthy human volunteers. Analysis of sera from patients with a history of cercarial dermatitis revealed elevated levels of cercarial-specific IgG, particularly for samples collected from adults (> 14 years old) comparedwith children (8–14 years old), although elevated levels of antigen-specific IgE were not detected. In terms of antigen recognition, IgG and IgE antibodies in the sera of both mice and humans preferentially bound an antigen of 34 kDa. The 34 kDa molecule was present in both homogenate of cercariae, as well as cercarial excretory/secretory products, and we speculate it may represent a major immunogen initiating the Th2-immune response associated with cercarial dermatitis.
Highlights
Bird schistosome cercariae of the genus Trichobilharzia penetrate the skin of vertebrates representing either compatible or noncompatible hosts
T. regenti infection induces IgM, IgG1 and IgG2b antibodies in mice against cercarial antigens
Antigen-specific IgG1 antibodies remained elevated over the remaining time course despite there being no further exposure to cercariae and the level at day 120 was still significantly greater (P < 0·001) compared with naïve mice (11·5-fold greater)
Summary
Bird schistosome cercariae of the genus Trichobilharzia penetrate the skin of vertebrates representing either compatible (waterfowl) or noncompatible (mammals, including man) hosts. Parasite invasion into the skin of waterfowl leads to the maturation of adult flukes, in mammals, the parasites are not able to complete their development and die at some point after infection. Infection of the skin leads to an inflammatory reaction known as swimmer’s itch or cercarial dermatitis, which develops after repeated contact with cercariae. The association between cercarial dermatitis in humans and exposure to avian schistosomes of the genus Trichobilharzia has long been recognized the disease is regarded as an emerging infection [1,2,3]. The disease manifests by maculo-papulo-vesicular eruption developing between 12 and 24 h after infection and is accompanied by intensive itching and, occasionally by erythema, fever, local lymph node swelling and oedema [5,6]
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