Complete 18S ribosomal RNA gene sequences were determined for 8 Eimeria species of chickens and for Eimeria bovis of cattle. Sequences were aligned with each other and with sequences from 2 Sarcocystis spp., Toxoplasma gondii, Neospora caninum, and 4 Cryptosporidium spp. Aligned sequences were analyzed by maximum parsimony to infer evolutionary relationships among the avian Eimeria species. Eimecia bovis was found to be the sister taxon to the 8 Eimeria species infecting chickens. Within the avian Eimeria species, E. necatrix and E. tenella were sister taxa: this clade attached basally to the other chicken coccidia. The remaining Eimeria spp. formed 3 clades that correlated with similarities based on oocyst size and shape. Eimeria mitis and Eimeria mivati (small, near spherical oocysts) formed the next most basal clade followed by a clade comprising Eimeria praecox. Eimeria maxima, and Eimeria brumetti (large, oval oocysts), which was the sister group to Eimeria acervulina (small, oval oocysts). The 4 clades of avian Eimeria species were strongly supported in a bootstrap analysis. Basal rooting of E. necatrix and E. tenella between E. bovis and the remaining Eimeria species and the apparent absence of coccidia that infect the ceca of jungle fowl all suggest that E. necatrix and E. tenella may have arisen from a host switch, perhaps from the North American turkey, Meleagris gallopavo.

Phylogenetic relationships among eight Eimeria species infecting domestic fowl inferred using complete small subunit ribosomal DNA sequences.

Publisher Summary This chapter discusses arrested development in nematode parasites. It explains that many parasitic nematodes have a resting stage or stages, further development depending on the reception of some stimulus or stimuli. This pause in development at some precise point in the life cycle of the parasite occurs only in certain hosts or circumstances or at certain times of the year, and it affects only some of the roundworms. The chapter describes parasitic genera and species within nine families, more than 30 genera and many more species helping to build up as complete a general picture as is possible at the present time. The similarities and differences are discussed. Evidence for a direct effect of immunity or of size of infection on arrested development is still not convincing, although host resistance may be crucial in some systems. Another view is that arrested development serves to synchronize the life cycle of the parasite either with that of the host or else with seasonal changes in the external environment, and it implies a response to signals to halt development, to cause it to be resumed, or to serve both functions.

Arrested development of nematodes and some related phenomena.

The paper is concerned with the principles upon which coccidia of the genus Eimeria may be characterized. Reference strains for comparative purposes usually are not available and the limitations of morphological data for speciation are discussed. The value of other parameters are considered such as host and site specificity, pathogenicity, immunological specificity, pre-patent period, sporulation time, enzyme variation, and DNA buoyant density. The weight afforded to each of these parameters for specific identification may vary according to the parasite and host studied. Determinations of physiological and behavioral characteristics that are now becoming available should be included in species definitions wherever possible.

Problems in the Identification of Species of Eimeria

A functional biology of parasitism

This article summarises the current knowledge of the rabbit coccidia and the disease they cause. Various aspects, such as life cycles, localisation in the host, pathology and pathogenicity, immunity and control, are discussed.

https://folia.paru.cas.cz/pdfs/fol/2009/03/01.pdf

Coccidia of rabbit: a review.

Factors contributing to the retardation of development of Obeliscoides cuniculi in rabbits

The development of second generation schizonts of Eimeria necatrix and E. tenella was studied with the electron microscope. Invasion of the crypt epithelial cells by merozoites of the first generation schizonts caused changes in the morphology of the infected cells and stimulated their migration into the lamina propria through breaks which appeared in the basement membrane of the crypts. Second generation schizonts developed in the lamina propria within these crypt cells whose epithelial origin was confirmed by their interconnection by desmosomes and tight junctions and by their possession of characteristic microvilli. A comparison is made between this invasion of the lamina propria by parasitized cells and invasion of connective tissue by malignant epithelial cells; the possible mechanisms involved are discussed.

Invasion of chicken caecal and intestinal lamina propria by crypt epithelial cells infected with coccidia.

Experimental infections of the domestic fowl with a variant of Eimeria praecox from the Ceylon jungle fowl.

Preparation of second generation merozoites of Eimeria necatrix free of host tissue.

Chickens were dosed orally with sporulated oocysts ofEimeria acervulina, E. brunetti, E. maxima, or E. praecox and the subsequent presence, in various tissues, of parasites capable of inducing patent infections was detected by transferring the tissues to coccidia-free recipients. Similar results were obtained with each of the 4 species studied, irrespective of whether initial development occurs in the superficial (E. praecox, E. brunetti) or crypt (E. acervulina, E. maxima) epithelium. Infection was transferable by gut scrapings and liver homogenates at all time intervals (3, 6, 12, 18, 24, and 36 hr postinoculation) studied. Infection was also transferable with blood and with splenic homogenates but not consistently. Transfers made within a short time of the inoculation of donors were more successful in producing patent infections in the recipients. In all transfers the prepatent period was normal for the species. These findings suggest that sporozoites enter the mucosa very shortly after inoculation, and some of them pass to the liver and spleen and then leave these tissues at a somewhat slower rate, possibly to reenter the mucosa. Sporozoites in the lamina propria of the gut were found within host mononuclear cells in all 4 species studied. Most of the cells harbouring E. maxima and some of those with E. praecox were identified as intraepithelial lymphocytes while all others could only be identified as agranular mononuclear cells that were not character- istically macrophages. Seven species of Eimeria parasitize the chick- en and, although their life cycles in the intestines of this host are fundamentally similar, there are some differences, for example, in the location of the early developmental stages. In the case of all 7 species, the sporozoites penetrate enterocytes of the villi (or the surface epithelium of the large intestine), but only E. brunetti and E. praecox begin their growth there. The first-generation schizonts of the other 5 species are formed in the enterocytes of the crypts. The sporozoites of E. tenella (Lawn and Rose, 1982) and E. necatrix

M. A. Fernando

Papers

Factors contributing to the retardation of development of Obeliscoides cuniculi in rabbits

Invasion of chicken caecal and intestinal lamina propria by crypt epithelial cells infected with coccidia.

Experimental infections of the domestic fowl with a variant of Eimeria praecox from the Ceylon jungle fowl.

Preparation of second generation merozoites of Eimeria necatrix free of host tissue.

Sporozoites intra- and extra-enterically