Parasitic contamination of fresh vegetables sold in some major markets and farms in Zaria

Abstract

Vegetables are important sources of dietary nutrients, as well as fiber and photochemicals. Many vegetables are eaten raw or partially cooked. However, vegetables are perishable; as such they are at their best when fresh. In the subtropics, different vegetables are readily available but they are prone to faecal contamination due to application of untreated human wastes on farmlands, or the use of unsafe water body for irrigation. The study was aimed at detecting parasites on seven different vegetable types randomly collected from two major markets and different farms in Zaria. A total of 346 samples were collected. The samples were subjected to sedimentation technique: 25 grams of each sample was washed in 225mL of normal saline, and the wash water was allowed to sediment overnight, followed by centrifugation at 3000 rpm for 5 min. Wet mounts of the sediments were examined for parasites on the light microscope using 10x and 40x objectives. Parasitic ova and larvae were identified with help of coloured parasitological atlases. A total of 90(26.0%) out of 346 samples were contaminated with parasites. Strongyloides stercoralis was the most occurring parasite (9.5%), followed by Ascaris lumbricoides  (6.9%), Hookworms (6.1%), Trichuris trichiura  (1.7%), whereas Enterobius  vermicularis and  Schistosoma haematobium were 0.9% each. Vegetable samples collected directly from the farms were significantly more contaminated (38.2%, P=0.001) than those from Sabon-Gari Market (32.9%) and Samaru Market (17.5%). Cabbage (42.0%), lettuce (32.0%) and spring onion (32.0%) significantly harboured more parasites (P=0.012) than rest of the vegetables. Also, hookworms significantly occurred in samples from the farms (11.0%), but samples from Sabon-Gari Market (11.4%) and Samaru Market (7.0%) were most contaminated with Strongyloides stercoralis.  The high level of parasitic contamination of vegetables from the farms is a direct indication of use of untreated human wastes and contaminated water for irrigation. The vegetables on reaching the market undergo some level of washing before sale, but this practice alone is not enough to make them safe for human consumption.