This weed is known to cause many health hazards which have now reached epidemic proportions. Agriculturists are concerned about P. hysterophorus affecting food and fodder crops, since the pollen and dust of this weed elicit allergic contact dermatitis in humans (Gunaseelan 1987; Morin et al. 2009). Dermatitis is a T cell-mediated immune injury and the disease manifests as itchy erythematous papules and papulovesicular lesions on exposed areas of the body (Akhtar et al. 2010). These effects have been related to cytotoxicity of the sesquiterpene lactone parthenin (Narasimban et al. 1984). Persons exposed to this plant for prolonged period manifest the symptoms of skin inflammation, eczema, asthma, allergic rhinitis, hay fever, black spots, burning and blisters around eyes. Parthenium hysterophorus also causes diarrhoea, severe papular erythematous eruptions, breathlessness and choking (Maishi et al. 1998). Exposure to P. hysterophorus pollens causes allergic bronchitis (Towers and Subba Rao 1992). Ramos et al. (2001) assessed the mutagenic potential of a crude extract of P. hysterophorus in the Salmonella/microsome (Ames) assay and the mouse bone marrow micronucleus test. However, it did not show genotoxic potential. Sharma et al. (2005) observed that the clinical pattern of Parthenium dermatitis progresses from airborne contact dermatitis to mixed pattern or chronic actinic dermatitis pattern. Eczema herpeticum is reported to complicate parthenium dermatitis. Sriramarao et al. (1993) worked on the use of murine polyclonal anti-idiotypic antibodies as surrogate allergens in the diagnosis of P. hysterophorus hypersensitivity. Parthenium-sensitive patients with rhinitis who had positive results on skin prick tests to P. hysterophorus pollen extracts responded with a positive skin reaction to mAb-2. Akhtar et al. (2010) studied the involvement of TH type cytokines in Parthenium dermatitis.
Exposure to P. hysterophorus also causes systemic toxicity in livestock (Gunaseelan 1987). Alopecia, loss of skin pigmentation, dermatitis and diarrhoea has been reported in animals feeding on P. hysterophorus. Degenerative changes in both the liver and kidneys and inhibition of liver dehydrogenases have been reported in buffalo and sheep (Rajkumar et al. 1988). The milk and meat quality of cattle, buffalo and sheep deteriorate on consumption of this weed (Lakshmi and Srinivas 2007). Significant reduction in rat WBC count after oral treatment of Parthenium extract signifies its immune system weakening ability (Yadav et al. 2010).
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