ABSTRACT

I. BACKGROUND Although Cryptosporidium was first described in the laboratory mouse by Tyzzer in 1907 (1), the medical and veterinary significance of this protozoan was not fully appreciated for another 70 years. The interest in Cryptosporidium has escalated tremendously over the last two decades as reflected in the number of publications, which increased from 80 in 1983 to 3150 citations in 2002 listed in MEDLINE. The early history of Cryptosporidium is extensively documented in several review articles and book chapters published recently (2-4). Taxonomically, C. parvum belongs to the phylum Apicomplexa (possessing apical complex), class Sporozoasida (reproduce by asexual and sexual cycles, with oocyst formation), subclass Coccidiasina (life cycle involving merogony, gametogeny, and sporogeny), order Eucoccidiida (schizogony occurs), suborder Eimeriina (independent microand macrogamy develop), family Cryptosporidiae (4 naked sporozoites within occysts-no sporocyst) (5). Like other enteric coccidia of vertebrates, Cryptosporidium has a monoxenous life cycle that is primarily completed within the gastrointestinal tract of a single host. It has, however, many unique features which distinguishes Cryptosporidium from other coccidia, of which the most obvious are the lack of host and organ specificity, resistance to antimicrobial agents, ability for autoinfection, and the curious location it occupies within the host cell membrane (6).