Host specificity of avian coccidia

Abstract

The term 'species specific' in reference to the host specificity of avian coccidia, has been used rather loosely for many years. A strong belief in strict species specificity has led to many new species of coccidia being described from oocysts isolated from the faeces of wild birds, primarily on the grounds that no coccidium had previously been described from that particular host species, A complicating factor is that animals can often have oocysts (Fig. I), passing through their intestines, of coccidia specific to other hosts. These 'foreign' oocysts might be derived directly from prey in the case of carnivorous birds, or indirectly from faecal contamination of their food in the case of granivorous birds, In the past, this has sometimes misled researchers into naming spurious new species which have subsequently been sunk in synonymies. But equally, there is the chance that an oocyst from a 'wrong' host might be correctly identified with the original description but incorrectly assumed to be capable of completing its life cycle in another host. The extremely wide host range recorded t for Isaspora lacazei is very suspect from this point of view. Hence, careful experimental procedures and a precise terminology regarding host specificity are clearly of paramount importance. Dunng the recent Georgia Coccidiosis Conference 2 discussion developed on the precision of terms used to describe the host specificit/es of avian coccidia, and I hope that this short review might stimulate further research in this area. Perusal of Pell~rdy's taxonomic monograph ~ shows that, w~thin the Galliformes at least, the range of hosts then known included extremely few congeneric species so that no reliable conclusions regarding species, as opposed to genus, specificity could be drawn at that t/me. However, the descriptions 3A of five nominal species of Eimeria from the Ceylon jungle fowl Gallus lafayetii* (Fig. 2) u g have at least partly resolved the problem. Two of these species, E. indentata and E. ~. d~minuta, were subsequently isolated from • Malaysian jungle fowl (Gallus gallus spadiceus) and have been synonymized with E. maxima and E. acervulina, respect/vely 5, and a further unidentified sample (E I ) from (2. lafayetii has been shown 6 to be E. praecax. The domesticated fowl is descended from the red jungle fowl G. galgallus, so perhaps this question might yet be answered in the affirmative, although more parasites should be studied first. However, some avian Eimena can cross the sub-family barrier; for example, E dispersa of the turkey Meleagris gallopava (Meleagridinae) can develop in the pheasant Phasianus colchicus, the partridge A/ectaHs graeca and the fowl G. gallus (Phasianinae) as well as in the bobwhite quail Colinus virglnianus (Odontophorinae)9; and E, co/chici of the common pheasant Phasianus calchicus can develop in Meleagris gallapava r°. lsospara species (sensu stricto) seem to be rare in the Galliformes, but one species, I. mayuri, from the peafowl Pavo cristatus (Phasianinae) cannot develop