Cockroaches as vectors of human enteric protozoa
Cockroaches frequently feed on human feces, and therefore they can disseminate cysts of enteric protozoans in the environment if such feces are contaminated (7, 16, 24, 25, 30, 31, 32). The important epidemiological role of cockroaches in transmission of intestinal Entamoeba histolytica-associated amoebiasis was demonstrated in 1971 (25) and in giardiasis in 1981 (16). German cockroaches (Blatella germanica) spread infectious Entamoeba histolytica/Entamoeba dispar and Giardia lamblia cysts at their visited sites (16, 30). A field survey carried out in 11 primary schools in an urban area of South Taiwan showed that over 25% of American cockroaches (Periplaneta americana) and 10% of Blatella germanica were positive for infectious Entamoeba histolytica/Entamoeba dispar cysts on the cuticle and in their digestive tracts (24). Laboratory experiments in which Blatella germanica and Periplaneta americana were exposed to Toxoplasma gondii and Sarcocystis oocysts demonstrated that these oocysts were infectious (as per mouse bioassay) while transported by cockroaches (27). Sarcocystis oocysts remained infectious on Periplaneta americana for at least 20 days after initial exposure to contaminated feces and for 5 days on Blatella germanica (27). However Toxoplasma gondii oocysts were infectious up to 10 days on Periplaneta americana and only immediately after the exposure on Blatella germanica (27).