The conceptual basis for a new classification of the coccidia

At the joint meeting of the 8th International Coccidiosis Conference and the Annual Scientific Meeting of the Australian Society for Parasitology in Palm Cove, Australia, in July 2001, a Controversial Roundtable was held on 'New classification of coccidia'. The aim of this Roundtable was to stimulate and encourage discussion and debate on current classification schemes for the group of parasitic protozoa known as the eimeriid coccidia. In the past, such classifications have been based only on phenotypic characters such as morphology, ultrastructure, life cycles, and host specificity. However, over the past 10-15 years, molecular phylogenetic studies on taxa of the eimeriid coccidia have revealed that several of the families, subfamilies, and genera that have been erected based on non-molecular characters are paraphyletic. Therefore, this Roundtable was an important forum for initial discussions on how a new and more comprehensive classification of the eimeriid coccidia, which takes into consideration both phenotypic and molecular characters, can be devised. The stimulus came from invited speakers who gave introductions into selected areas of taxonomy and classification. Following these introductions, a more general discussion with the audience addressed potential steps that may be taken in future work. This review is the immediate outcome of the Roundtable. It describes advantages and disadvantages of the use of phenotypic or molecular characters as the base for taxonomic schemes for eimeriid coccidia. It gives specific examples for drawbacks of current classifications based only on phenotypic characters as well as potential pitfalls associated with the use of only molecular phylogenies. It addresses current controversies as well as rules of taxonomy and nomenclature relevant for the eimeriid coccidia. Finally, it recommends the establishment of an international group of scientists to meet on a regular basis, stimulate further discussions, and give direction on how the final goal, i.e. a proposal for a revised, and widely accepted, classification of the eimeriid coccidia, may be achieved.     

Cryptosporidium molnari n. sp. (Apicomplexa: Cryptosporidiidae) infecting two marine fish species,Sparus aurata L. and Dicentrarchus labrax L

Cryptosporidium molnari n. sp. is described from two teleost fish, the gilthead sea bream (Sparus aurata L.) and the European sea bass (Dicentrarchus labrax L.). The parasite was found mainly in the stomach epithelium and seldom in the intestine. Oocysts were almost spherical, with four naked sporozoites and a prominent residuum, and measured 3.23-5.45 x 3.02-5.04 (mean 4.72 x 4.47) microm in the type host, gilthead sea bream (shape index 1-1.17, mean 1.05). Sporulation was endogenous, as fully sporulated oocysts were found within the fish, both in the stomach epithelium and lumen, and in faeces. Oocysts and other stages of C. molnari fit most of the diagnostic features of the genus Cryptosporidium, but differ from hitherto described species, including piscine ones. All stages were located within a host contributed parasitophorous vacuole lined by a double host microvillar membrane. Merogonial and gamogonial stages appeared in the typical extracytoplasmic position, whereas oogonial and sporogonial stages were located deeply within the epithelium. Ultrastructural features, including the characteristic contact zone of the parasite with the host epithelial surface, were mostly coincident with those of other Cryptosporidium spp. Mitochondria were found in dividing meronts, merozoites, microgamonts and sporozoites. Pathological effects were more evident in gilthead sea bream, which also exhibited a clearly higher prevalence (24.4 versus 4.64% in sea bass). External clinical signs, consisting of whitish faeces, abdominal swelling and ascites, were rarely observed, in contrast with important histopathological damage. The wide zones of epithelium invaded by oogonial and sporogonial stages appeared necrotic, with abundant cell debris, and sloughing of epithelial cells, which detached to the lumen. No inflammation reaction was observed and the cellular reaction was limited to the cells involved in the engulfing of intraepithelial stages and debris, probably macrophages.     

Multiple oral inoculations with Cryptosporidium parvum as a means of immunization for production of monoclonal antibodies

Abstract Oral immunization of suckling mice with Cryptosporidium parvum results in a humoral response to a limited set of antigens. Six-day-old BALB/c mice were each inoculated orally with 1 × 10⁶ viable oocysts and subsequently administered oral inoculations of 2 × 10⁶ viable oocysts at 30 and 60 days following the primary infection. After 45 days, mice were boosted with 1 × 10⁶ oocysts orally, plus soluble extracts equivalent to 2 × 10⁶ and 1 × 10⁶ oocysts given intravenously and intraperitoneally, respectively. Four days later, splenic lymphocytes were fused to Ag8 myeloma cells. Using this method, we have been able to select for monoclonal antibodies that predominately recognize sporozoite surface and apical complex antigens.     

Ultrastructure des stades végétatifs d'Aggregata eberthi Labbé: le trophozoïte et le schizonte

Summary The growing stages of Aggregata eberthi, in the cuttlefish on the one hand (sexual generation), and in the crab on the other hand (asexual generation), are investigated.The fine structure of the two stages is comparable. The cytoplasmic inclusions are those of all Sporozoa: mitochondria with short inner tubuli, dictyosomes in relationship with ergastoplasm, paraglycogen granules, lipoid vacuoles. The big nucleus contains a voluminous nucleolus. The wall consists in three unit-membranes, holed by micropores. Under the wall occurs an ergastoplasmic formation of a peculiar type.The most striking difference between the trophozoïte and the schizont is the morphological aspect: the first one shows deep invaginations and there are protuberances on the second one.

Ce travail a pu être effectué grâce à la collaboration technique de Madame C. Breda et Mademoiselle R. Coulombez, que nous remercions vivement.     

Biology and pathogenicity of Eimeria neodebliecki Vetterling, 1965 in experimentally infected pigs

The endogenous development and pathogenicity of Eimeria neodebliecki Vetterling, 1965 are described in weaned pigs inoculated with 250 000 oocysts. The endogenous stages developed within the apical cytoplasm of the enterocytes of the middle and posterior jejunum. The asexual development comprised two generations of meronts. Immature and mature meronts were found in groups up to five per host cell. The first fully developed macrogametes and mature microgamonts were seen at 9 days post-infection (DPI). The prepatent period was 10 days, and the patent period lasted 6–8 days. Sporulation of oocysts was completed within 12 days at 25°C, and 16 days at 20°C. E. neodebliecki infection produced clinical signs of coccidiosis in weaned pigs which developed frothy or mucoid diarrhea from 9 to 12 DPI. Pathological changes were situated in the second half of the small intestine, with the predilection for the posterior jejunum. At 9 and 10 DPI, macroscopically, ranged from catarrhal to focal, pseudomembranous inflammatory lesions. Histopathological and SEM examinations revealed moderate villous atrophy with focal epithelial erosions and fibrinonecrotic material at the villous tips. E. neodebliecki is pathogenic for pigs and can be associated with clinical manifestation of diarrhea, stunted growth and poor condition in pigs.     

Switch,disperse, repeat: host specificity is highly flexible in rodent-associated Eimeria

Interplay between conserved host specificity and occasional host switches is an important process determining the evolution of host-parasite systems. Here, we address the dynamics of host switches at the population level in rodent-associated Eimeria. Focusing mainly on two ecologically similar host groups, Murinae and Arvicolinae, we show that the Eimeria infecting those hosts form a complex system of many genetic lineages with different host specificities. The broad geographic distribution of lineages indicates that they are well-established genetic forms which retained their host specificities while spreading across large geographic areas. We also demonstrate that genetic structure is only partially reflected by morphological traits.     

A Note on Sporozoa of Undetermined Taxonomic Position in an Armadillo and a Heifer Calf

A sporozoan parasite of undetermined taxonomic position is described in the nine-banded armadillo, Dasypus novemcinctus, from British Honduras, Central America. Schizonts, giving rise to approximately 60 merozoites, are produced in the parenchyma cells of the liver and in the endothelial cells of the brain capillaries: rupture of the schizonts stimulates conspicuous foci of inflammatory response. No sexual stages were observed. A similar parasite is recorded in the lung and liver of a heifer calf, Bos taurus, from England. The possible relationship of these parasites within the Sporozoa is discussed.