Differential sources of host species heterogeneity influence the transmission and control of multihost parasites

Controlling parasites that infect multiple host species often requires targeting single species that dominate transmission. Yet, it is rarely recognised that such ‘key hosts’ can arise through disparate mechanisms, potentially requiring different approaches for control. We identify three distinct, but not mutually exclusive, processes that underlie host species heterogeneity: infection prevalence, population abundance and infectiousness. We construct a theoretical framework to isolate the role of each process from ecological data and to explore the outcome of different control approaches. Applying this framework to data on 11 gastrointestinal parasites in small mammal communities across the eastern United States reveals variation not only in the magnitude of transmission asymmetries among host species but also in the processes driving heterogeneity. These differences influence the efficiency by which different control strategies reduce transmission. Identifying and tailoring interventions to a specific type of key host may therefore enable more effective management of multihost parasites.     

Systematics of the Eimerian Parasites from North American Snakes of the Family Colubridae,and their Prevalence in the Colubrids of Iowa*

A survey of 117 Iowa snakes, representing 18 species within 12 genera, revealed the presence of 6 species of Eimeria, 5 of which are described as new and 1 of which (E. zamenis) is redescribed. Those species found, the average length-width dimensions of their oocysts ( in micrometers ), and the respective hosts from which they were isolated were as follows: E. attenuata sp. n., 22.2 × 12.6, from 1 of 25 red-sided garter snakes [Thamnophis sirtalis parietalis (Say)] and 1 of 14 northern water snakes [Natrix sipedon sipedon (Linnaeus)]; E. iowaensis sp. n., 17.8 × 14.5, from 1 of 25 redsided garter snakes; E. hydrophis sp. n., 15.4 × 10.9, from 5 of 14 northern water snakes and 1 of 1 diamond-backed water snake [N. rhombifera rhombifera (Hallowell)]; E. helmisophis sp. n., 13.8 × 10.6, from 1 of 5 western worm snakes [Carphophis amoenus vermis (Kennicott)]; E. collanuli sp. n., 33.1 × 18.3, from 1 of 14 prairie ring-neck snakes (Diadophis punctatus arnyi Kennicott), and E. zamenis, 31.0 × 17.0, from 1 of 6 eastern yellow-bellied racers (Coluber constrictor flaviventris Say) and 1 of 1 eastern milk snake [Lampropeltis triangulum triangulum (Lacépède)]. The overall infection rate for the 117 snakes examined was 9.2%; these data are tabulated. In addition, the possible synonymy of E. lampropeltis with E. zamenis is considered, and the probable status of E. attenuata, E. hydrophis, E. zamenis, and E. annea, as parasites of multiple host species, is reviewed with regard to the phylogenetic relationships of the respective hosts from which they have been reported.     

Neospora caninum: infection induced IL-10 overexpression in rat astrocytes in vitro

The effect of Neospora caninum, a parasite that causes abortion and neuromuscular changes, has been investigated on a major population of neural cells, the astrocytes. Highly enriched astroglial primary cultures obtained from neonatal rats were infected after 21 days of culture. Astroglial reactivity, IL-10 and IFN-gamma expression, and cell viability (lactate dehydrogenase activity, metabolization of tetrazolium salt, and trypan blue exclusion assay) have been investigated after 24 and 72 h of infection. Astroglial hypertrophy, gliofilament reorganization, metabolic changes suggesting hypoxia and a strong IL-10 release have been observed in the infected cells. These results show that neural cells are targets for the parasite and that astrocytes may contribute to the CNS immune response to the parasite.     

Genetic Manipulation in Δku80 Strains for Functional Genomic Analysis of Toxoplasma gondii

Targeted genetic manipulation using homologous recombination is the method of choice for functional genomic analysis to obtain a detailed view of gene function and phenotype(s). The development of mutant strains with targeted gene deletions, targeted mutations, complemented gene function, and/or tagged genes provides powerful strategies to address gene function, particularly if these genetic manipulations can be efficiently targeted to the gene locus of interest using integration mediated by double cross over homologous recombination.Due to very high rates of nonhomologous recombination, functional genomic analysis of Toxoplasma gondii has been previously limited by the absence of efficient methods for targeting gene deletions and gene replacements to specific genetic loci. Recently, we abolished the major pathway of nonhomologous recombination in type I and type II strains of T. gondii by deleting the gene encoding the KU80 protein^1,2. The Δku80 strains behave normally during tachyzoite (acute) and bradyzoite (chronic) stages in vitro and in vivo and exhibit essentially a 100% frequency of homologous recombination. The Δku80 strains make functional genomic studies feasible on the single gene as well as on the genome scale^1-4.Here, we report methods for using type I and type II Δku80Δhxgprt strains to advance gene targeting approaches in T. gondii. We outline efficient methods for generating gene deletions, gene replacements, and tagged genes by targeted insertion or deletion of the hypoxanthine-xanthine-guanine phosphoribosyltransferase (HXGPRT) selectable marker. The described gene targeting protocol can be used in a variety of ways in Δku80 strains to advance functional analysis of the parasite genome and to develop single strains that carry multiple targeted genetic manipulations. The application of this genetic method and subsequent phenotypic assays will reveal fundamental and unique aspects of the biology of T. gondii and related significant human pathogens that cause malaria (Plasmodium sp.) and cryptosporidiosis (Cryptosporidium).     

A simple and reliable method of producing in vitro infections of cryptosporidium parvum (apicomplexa)

Abstract A variety of techniques have been used to infect cell monolayers in culture with the protozoan, Cryptosporidium parvum . However, most of these methods rely on the use of trypsin and/or bile salts to excyst sporozoites in vitro, followed by washing sporozoites free of excystation solution prior to their addition to subconfluent monolayers. This method not only increases the amount of time required to establish infections in vitro, but also results in prolonged exposure of free sporozoites to environmental conditions. Here we report a simple, fast, and efficient method of obtaining consistent infections of C. parvum in cell monolayers. This technique relies on the ability of the parasite to excyst at 37°C but not at room temperature following pretreatment with sodium hypochlorite. By adding surface-sterilized oocysts directly to monolayers, sporozoites have access to host cells immediately upon excystation.     

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.     

Isospora Normanlevinei N. Sp. and Isospora Coluzzii N. Sp. (Apicomplexa: Eimeriidae) In Emberiza Cirlus (Cirl Bunting) (Passeriformes-Emberizidae)

ABSTRACT. The morphological characteristics of two new species of Isospora observed in Emberiza cirlus (Cirl Bunting) from Italy are reported. the oocysts of Isospora normanlevinei n. sp. are spherical or sub-spherical, with a smooth double-layered wall, and measure 24.2 times 23.7 (21.0-26.5 times 21.5-25.5) μm; each oocyst contains 2 to 10 polar granules. No micropyle or residuum was observed. the piriform sporocysts measure 19.4 times 11.2 (17.0-21.0 times 10.0-12.5) μm and contain a dispersed residuum. the Stieda body is flat; the substiedal body, with scattered clear and dark granules, may be either symmetrical or asymmetrical. the oocysts of I. coluzzii n. sp. are asymmetrical and rounded shape and measure 28.6 times 24.2 (25.0-31.5 times 21.5-26.0) μm. the oocyst has a double-layered wall and 2 to 3 polar granules. Neither micropyle nor residuum is present. the sub-ellipsoidal sporocyst, measuring 18.2 times 10.0(16.5-20.0 times 9.0-11.0) μm, has a dispersed sporocyst residuum. the Stieda complex is symmetrical.     

Divalent Cation and ATP Dependent Motility of Toxoplasma gondii Tachyzoites After Mild Treatment with Trypsin

ABSTRACT. Large percentages of Toxoplasma gondii tachyzoites could be induced to display two types of movement associated with active invasive behavior by exposing them for 1 min to 0.002% trypsin in phosphate-buffered saline (PBS). The motile activity, consisting of clockwise rotation around the posterior end (about 20 revolutions per min) and twirling-gliding over a poly-L-lysine substrate (1.2 ± 0.2 μm/s standard deviation), was observed and recorded by video-enhanced contrast microscopy. The number of active tachyzoites reached a maximum 1 min after trypsinization; the motile response of the population lasted for about 5 min. Activation was prevented by soybean trypsin-inhibitor, and could not be induced again in previously treated specimens. Electron-microscopy of trypsinized tachyzoites fixed in the presence of ruthenium-red revealed discrete discontinuities of the plasma membrane, which sealed within 90 min after washing with PBS. Treated tachyzoites were able to invade cultured epithelial cells with a higher relative infectivity than that of untreated parasites. Perfusion of trypsinized tachyzoites with 1 mM of either CaCl₂ or MgCl₂ and 1 mM ATP increased the number of activated parasites to over 60%; on the other hand, all induced motility was inhibited or blocked by agents that chelate divalent cations. The present preparation, which provided the first serial illustrations of T. gondii movements induced by a defined chemical stimulus, may offer a useful experimental model for the study of motility in this parasite.     

Isospora thibetana N. Sp. (Apicomplexa, Eimeriidae), a Parasite of the Tibetan Siskin (Serinus thibetanus=Carduelis thibetanus) (Passeriformes, Fringillidae)

Tibetan siskins are birds native to the Himalayan region often imported into Italy for commercial purposes. Fecal examination of 45 imported subjects with clinical signs of diarrhoea revealed the presence of a large number of coccidian oocysls. After sporulation, accomplished by mixing feces with 2.5 % (w/v) acqueous K₂Cr₂O₇ at room temperature (22° C ± 1° C), exogenous stages of an Isospora species were revealed. The oocysts of this Isospora are spherical, have a bilayered colorless wall, and average 23.24 μm × 23.05 μm; oocyst residuum and micropyle are absent, while an oval polar granule is rarely present. The elliptical sporocysts average 18.44 μm × 10.97 μm and the Stieda body protrudes slightly from the end of the sporocyst. A spherical sporocyst residuum is present though it sometimes consists of scattered granules. The spindle-shaped sporozoites average 11.53 μm × 2.86 μm, and have two refractile bodies. The taxonomic position of the tibetan siskin is controversial. Some authors include this species in the genus Serinus , while others include it in the genus Carduelis. The coccidian species isolated from these tibetan siskins was, for this reason. compared with the Isospora species previously described both in the genus Carduelis and in the genus Serinus. As a result of this comparison a new species. Isospora thibetana , was named. In the intestine of dead subjects, oocysts were found only in the ileum where the mucosa was greatly thickened and presented a heavy leucocytic infiltration consisting mainly of lympho-monocytic cells. A similar infiltration was observed in liver and lungs as well.