A high rate of cross-sensitivity between Parthenium hysterophorus and Xanthium strumarium in Indian patients with contact dermatitis

Parthenium hysterophorus is well known to produce contact dermatitis in India. Xanthium strumarium is another weed also belonging to the Compositae family present in India since much earlier times, but not recognised among the plants causing contact dermatitis. We have found a very high rate of cross-sensitivity between the two plants in patients presenting air-borne contact dermatitis. Of the 28 patients with air-borne contact dermatitis. 22 revealed positive patch tests with aqueous extracts of both plants, one patient showed a negative patch test with Parthenium hysterophorus and a positive test with Xanthium strumarium , while five patients were negative with both plants. In a control group of 15 patients with contact dermatitis due to other agents, only one patient showed a positive patch test with Xanthium strumarium , while the patch test with Parthenium hysterophorus was negative. Patch tests performed with serial 10-fold dilutions of standard extracts of both plants to determine the degree (titre) of contact hypersensitivity (TCH) revealed variable litres in different patients. Some patients had a much higher titre with Parthenium hysterophorus while others had a higher titre with Xanthium strumarium. The antigen in Xanthium strumarium , like that of Parthenium hysterophorus , could be extracted with water, acetone, ethanol, chloroform, benzene, ether and carbon tetrachloride. Infra-red spectrophotometry of extracts in ether revealed similar spectra in the two plants. The antigens in the two plants seem lo be very similar.