Sarcocystis dubeyi (Huong and Uggla, 1999) infection in water buffaloes (Bubalus bubalis) from Egypt

Water buffaloes (Bubalus bubalis) are intermediate hosts for 4 species of Sarcocystis , i.e., Sarcocystis fusiformis and Sarcocystis buffalonis with cats as definitive hosts; Sarcocystis levinei with dogs as definitive hosts; and Sarcocystis dubeyi with an unknown definitive host but thought to be zoonotic. Currently, the latter species has been identified with certainty only from Vietnam. In the present study, sarcocysts of S. dubeyi are reported in 11 (30%) of 35 Egyptian water buffaloes from which the esophageal muscles were examined histologically. Sarcocysts were microscopic, measuring 180-250 × 70-110 μm in size. Ultrastructurally, the sarcocyst wall was 3.5-6.5 μm thick and had palisade-like villar protrusions which give it a striated appearance. The villar protrusions contained microtubules that were distributed along the whole villus. This is the first report of S. dubeyi from water buffaloes in Egypt.     

Phylogenetic analysis of Alloglossidium Simer, 1929 (Digenea: Plagiorchiiformes: Macroderoididae) with discussion of the origin of truncated life cycle patterns in the genus.

Alloglossidium comprises 9 species of North American plagiorchiiform digeneans using ictalurid catfish, freshwater crustacea, and hirudinid leeches as definitive hosts. Two hypotheses about the evolution of this array of definitive hosts were examined using phylogenetic systematic analysis. Two most parsimonious trees, based on 15 homologous series derived from morphological data, each indicated the 2 species utilizing ictalurid catfish definitive hosts are basal members of the group, whereas the 2 species using freshwater crayfish definitive hosts and the 5 utilizing leech definitive hosts each comprise relatively derived monophyletic sister groups. The results suggest that species using crustaceans as definitive hosts are derived by life cycle truncation, whereas those using leeches as definitive hosts appear to be derived through a switch from crustaceans to leeches.     

Distance decay of similarity among parasite communities of three marine invertebrate hosts

The similarity in species composition between two communities generally decays as a function of increasing distance between them. Parasite communities in vertebrate definitive hosts follow this pattern but the respective relationship in intermediate invertebrate hosts of parasites with complex life cycles is unknown. In intermediate hosts, parasite communities are affected not only by the varying vagility of their definitive hosts (dispersing infective propagules) but also by the necessary coincidence of all their hosts in environmentally suitable localities. As intermediate hosts often hardly move they do not contribute to parasite dispersal. Hence, their parasite assemblages may decrease faster in similarity with increasing distance than those in highly mobile vertebrate definitive hosts. We use published field survey data to investigate distance decay of similarity in trematode communities from three prominent coastal molluscs of the Eastern North-Atlantic: the gastropods Littorina littorea and Hydrobia ulvae, and the bivalve Cerastoderma edule. We found that the similarity of trematode communities in all three hosts decayed with distance, independently of local sampling effort, and whether or not the parasites used the mollusc as first or second intermediate host in their life cycle. In H. ulvae, the halving distance (i.e. the distance that halves the similarity from its initial similarity at 1 km distance) for the trematode species using birds as definitive hosts was approximately two to three times larger than for species using fish. The initial similarities (estimated at 1 km distance) among trematode communities were relatively higher, whereas mean halving distances were lower, compared to published values for parasite communities in vertebrate hosts. We conclude that the vagility of definitive hosts accounts for a high similarity at the local scale, while the strong decay of similarity across regions is a consequence of the low probability that all necessary hosts and suitable environmental conditions coincide on a large scale.     

Can helminth community patterns be amplified when transferred by predation from intermediate to definitive hosts?

Helminth communities in definitive hosts are formed by the acquisition of packets of larvae arriving each time an intermediate host is consumed. It is thus possible that associations between parasite species or other aspects of community structure get transferred from intermediate to definitive hosts. Earlier computer simulations showed that associations between 2 parasite species, in particular positive associations, could be transferred up the food chain. Here, we alter some of the assumptions of previous models and generate new simulations of several ways in which source infracommunities in intermediate hosts can be transferred to target infracommunities in definitive hosts. In particular, we introduced nonrandom selection of intermediate hosts by predatory definitive hosts, to mimic the phenomenon of host manipulation by parasites; this consisted in biasing predation toward intermediate hosts harboring a certain parasite species. Overall, our results show that positive covariances between 2 parasite species can not only be transferred but can also be amplified during transmission to definitive hosts; significant covariance between parasite species can even appear in the definitive hosts when none existed in the intermediate hosts. Negative covariance was not as readily transferred to definitive hosts and amplified, in part because of properties of the presence-absence covariance index. Amplification of covariance results from intermediate host manipulation as well as from other processes taking place during transmission. These results suggest that the patterns of association between helminth species in definitive hosts cannot be taken to reflect the processes acting inside those hosts: they may simply be inherited, with amplification, from intermediate hosts.     

Preliminary report of histopathology associated with infection with tongue worms in Australian dogs and cattle

Tongue worms utilise herbivorous mammals as intermediate hosts and reside in the nasopharynx of carnivores as their definitive hosts. A recent study in south eastern Australia showed an unexpectedly high infection (67%) of wild dogs with these parasites. The present study aimed at determining the pathogenicity of the parasite in both definitive (dog) and intermediate (cattle) hosts by histopathology. The definitive host showed multifocal haemorrhage of the interstitium of the nasal mucosa, multifocal mucosal erosion, congestion and haemorrhage, with haemosiderin laden macrophages present in those foci and distortion and destruction of the nasal mucosa. Histopathologic examination of lymph nodes from an infected cow showed diffuse eosinophilic granulomatous necrotising lymphadenitis and perinodal panniculitis with intralesional parasitic remnants and comparatively large numbers of eosinophils. A large, ~300–500?μm diameter, area of necrosis was also observed in one lymph node. This is the first time a study has been undertaken in Australia to determine the pathogenicity of tongue worms in both their definitive and intermediate hosts. This is a preliminary study and to properly estimate the health impact of infection with this pathogenic parasites on Australian production and companion animals more studies are necessary.     

The palearctic oystercatcher Haematopus ostralegus, a natural definitive host for Gymnophalloides seoi

In order to verify the role of migrating birds as natural definitive hosts for Gymnophalloides seoi (Gymnophallidae), Palearctic oystercatchers, Haematopus ostralegus, were caught from several western coastal areas in the Republic of Korea and examined for intestinal flukes. Five (71.4%) of 7 oystercatchers were infected with 302-1,660 (mean 892) adult G. seoi. In intestinal sections of the host, worms were found in the intervillous space of the mucosal layer. We conclude that the oystercatcher is a natural definitive host for G. seoi.     

Focal Philophthalmus gralli infection possibly persists in Melanoides tuberculata over two years following the definitive hosts' removal

Philophthalmosis is a zoonotic disease associated largely with the spread of the invasive freshwater snail Melanoides tuberculata, serving as an intermediate host. Here we examined Philophthalmus gralli focal fenced infection site reported recently as being associated with Tinamus major and M. tuberculata in Alajuela, Costa Rica. Removal of the definitive hosts allowed us to address also the long-term survival strategy of the parasite. Initially, the snail intermediate hosts displayed high prevalence of P. gralli infection across all its age cohorts. Two years following the removal of definitive hosts, the infection rate decreased by one order of magnitude, while the snails aging less than one year displayed zero infection prevalence. Additionally, phylogenetic analysis of mitochondrial (ND1) and nuclear (ITS1, ITS2) DNA loci revealed negligible intrasite DNA variability of the specimens obtained at the study site in Costa Rica (but not of those obtained earlier in Peru or New Zealand), supporting strongly the hypothesis on focal origin of the infection. The observed dynamics of infection suggests the explanation for the high variability in P. gralli prevalence in intermediate hosts experienced worldwide. We noticed that the reports claiming > 20% prevalence of M. tuberculata infection by P. gralli originated exclusively from foci with known eye infection of the definitive hosts, while the P. gralli infection penetrance < 2% is typically associated with sites, where the infection of definitive hosts was not observed, suggesting that the infected definitive hosts were present onsite only in the past, or were present only at a site upstream or downstream of the respective sampling site. Thus, this is the first evidence on the possible persistence of eye-trematode infection site for over two years following the last confirmed outbreak in its adult hosts.     

Morphological variation of Moniliformis moniliformis (Bremser 1811) Travassos 1915 and Moniliformis clarki (Ward 1917) Chandler 1921.

A two-way fixed model analysis of variance was used to test Moniliformis moniliformis and M. clarki for inter- and intraspecific differences with respect to 7 morphological characters used to distinguish species of the genus. M. clarki was sexually dimorphic in more characters than was M. moniliformis when specimens from their usual definitive hosts, Spermophilus tridecemlineatus and Rattus norvegicus, respectively, were compared. More characters were sexually dimorphic in both species reared in hamsters, Mesocricetus auratus, than in their usual definitive hosts or M. clarki from rats. Moniliformis clarki and M. moniliformis (n = 25 each sex, each species) from their usual hosts were significantly different at the 1% level in 6 of 7 characters studied. Further M. clarki of either sex from ground squirrels did not differ significantly in any of the 7 characters from those of the same sex from rats. When reared in hamsters, the range in number of longitudinal rows of proboscis hooks of female M. moniliformis included that of M. clarki, but the 2 species were distinct in each of the other features which distinguished them in rats and ground squirrels.     

Species-specific prevalence of mermithid parasites in populations of six congeneric host caddisflies of Ecnomus McLachlan, 1864 (Trichoptera: Ecnomidae)

Mermithid nematodes are entomophagous parasites and, despite being present in diverse aquatic insects, studies of caddisflies acting as definitive hosts are few and the ecological impacts on host populations are largely unknown. During a four-year study in a stream in southeastern Australia, parasitic mermithid worms were commonly found inside adult caddisflies, but only species of the genus Ecnomus McLachlan, 1864 (Ecnomidae). Ecnomus were the definitive host and parasite prevalence ranged from <1% to nearly 50% across six species. Species-specific prevalence varied little between years and was typically higher in males than in females. Parasite intensity ranged from 1 to 6 (median = 1), but did not vary between species or sexes. Infected hosts could fly, but were castrated and died when worms emerged. High prevalence and virulence (reproductive failure and death of the host) suggests that these parasites could potentially play a role in the population dynamics of some Ecnomus spp.     

Evolution of complex life cycles in trophically transmitted helminths. I. Host incorporation and trophic ascent

Links between parasites and food webs are evolutionarily ancient but dynamic: life history theory provides insights into helminth complex life cycle origins. Most adult helminths benefit by sexual reproduction in vertebrates, often high up food chains, but direct infection is commonly constrained by a trophic vacuum between free‐living propagules and definitive hosts. Intermediate hosts fill this vacuum, facilitating transmission to definitive hosts. The central question concerns why sexual reproduction, and sometimes even larval growth, is suppressed in intermediate hosts, favouring growth arrest at larval maturity in intermediate hosts and reproductive suppression until transmission to definitive hosts? Increased longevity and higher growth in definitive hosts can generate selection for larger parasite body size and higher fecundity at sexual maturity. Life cycle length is increased by two evolutionary mechanisms, upward and downward incorporation, allowing simple (one‐host) cycles to become complex (multihost). In downward incorporation, an intermediate host is added below the definitive host: models suggest that downward incorporation probably evolves only after ecological or evolutionary perturbations create a trophic vacuum. In upward incorporation, a new definitive host is added above the original definitive host, which subsequently becomes an intermediate host, again maintained by the trophic vacuum: theory suggests that this is plausible even under constant ecological/evolutionary conditions. The final cycle is similar irrespective of its origin (upward or downward). Insights about host incorporation are best gained by linking comparative phylogenetic analyses (describing evolutionary history) with evolutionary models (examining selective forces). Ascent of host trophic levels and evolution of optimal host taxa ranges are discussed.     

Ingestion of Neospora caninum tissue cysts by Mustela species

Dogs are a definitive host of Neospora caninum, a protozoal parasite that causes abortion in cattle. Mustelids were tested to determine if they could also be definitive hosts. The procedures used were the same as those previously used to test dogs. Ermine (Mustela erminea), weasels (Mustela frenata) and ferrets (Mustela putorius) were fed N. caninum-infected mice. Neospora caninum oocysts were not observed. Mustelid faeces were fed to mice. The mice did not seroconvert and N. caninum was not detected in murine brains using tissue culture and PCR. The hypothesis that Mustela spp. are definitive hosts of N. caninum is not supported.     

More than meets the eye: detecting cryptic microgeographic population structure in a parasite with a complex life cycle

Nonrandom recruitment of parasites among hosts can lead to genetic differentiation among hosts and mating dynamics that promote inbreeding. It has been hypothesized that strictly aquatic parasites with intermediate hosts will behave as panmictic populations among hosts because ample opportunity exists for random mixing of unrelated individuals during transmission to the definitive host. A previous allozyme study on the marine trematode Lecithochirium fusiforme did not support this hypothesis; in that, there was genetic differentiation among, and significant heterozygote deficiencies within, definitive hosts. We revisit this system and use microsatellites to obtain multilocus genotypes. Our goal was to determine whether cryptic subgroups and/or the presence of clones could account for the apparent deviation from 'panmixia'. We find strong evidence for cryptic subdivision (three genetic clusters) that causes the Wahlund effect and differentiation among definitive hosts. After accounting for these cryptic groups, we see panmictic genetic structure among definitive hosts that is consistent with the 'high mixing in aquatic habitats' hypothesis. We see evidence for cotransmission of clones in all three clusters, but this level of clonal structure did not have a major impact in causing deviations from Hardy-Weinberg equilibrium, and only affected genetic differentiation among hosts in one cluster. A cursory examination of the data may have led to incorrect conclusions about nonrandom transmission. However, it is obvious in this system that there is more than meets the eye in relation to the actual make-up of parasite populations. In general, the methods we employ will be useful for elucidating hidden patterns in other organisms where cryptic structure may be common (e.g. those with limited morphology or complex life histories).     

Do hemoglobin and hemocyanin impair schistosoma killing by no?

Nitric oxide (NO) possesses antiparasitic effects on both Protozoa and Metazoa in definitive and intermediate hosts as well as in vectors. Here, we postulate that hemoglobin and hemocyanin may impair Schistosoma killing by NO in the definitive and intermediate hosts. Interestingly, hemoglobin, myoglobin, and neuroglobin may protect Plasmodium and Trypanosoma from the antiparasitic effects of NO.     

The pig as a host for Schistosoma mekongi in Laos.

A survey of helminths in domestic pigs was conducted in Khong District, Laos, to elucidate if these domestic animals could act as definitive hosts for Schistosoma mekongi and to obtain a general overview of their helminthological infection status. Fecal samples were collected from 98 pigs. Twelve pigs (12.2%) were found to excrete S. mekongi eggs. Infection was confirmed by detection of S. mekongi eggs in tissues of liver, rectum, and cecum of 2 pigs. A total of 75.8% of the pigs was infected with 1 or more helminth species. This study showed that pigs may act as a definitive host for S. mekongi.     

Temporal variation in prevalence and abundance of metacercariae in the pulmonate snail Lymnaea stagnalis in Chany Lake, West Siberia, Russia: long-term patterns and environmental covariates

Infrapopulations of trematode metacercariae were monitored in the snail Lymnaea stagnalis over 17 yr (1982-1999) at Chany Lake, Novosibirskaya Oblast', Russia. Eighteen trematode species were recorded. Patterns of occurrence varied from 4 species (Echinoparyphium aconiatum, Echinoparyphium recurvatum, Moliniella anceps, and Cotylurus cornutus) that persisted at relatively high prevalence (> 60% of samples) across sites, seasons, and years, to species that were very rare and sporadic in occurrence. The stability of the 4 common species was probably because of their occurrence either in a wide range of definitive hosts or in a host adapted to the extreme abiotic changes that occurred from year to year in these wetlands. The prevalence and mean abundance of C. cornutus were negatively correlated with water level in the wetlands; its prevalence was also correlated with water temperature. The mean abundance of M. anceps was positively correlated with water level. The most probable explanation for the cyclic dynamics of infections of the common species is change in population sizes and densities of definitive and intermediate hosts, which mediated cyclic alterations in water levels.     

Phylogenetic analysis of the class Sporozoea (phylum Apicomplexa Levine, 1970): evidence for the independent evolution of heteroxenous life cycles

A phylogenetic analysis of representative genera in the class Sporozoea was undertaken using biological and morphological features to infer evolutionary relationships among the widely recognized groups in the class. Gregarines were used as a functional outgroup to the remaining sporozoa (adeleids, eimeriorins, haemosporinids, and piroplasms). The piroplasms were shown to be closely related to the adeleid parasites. Species of Babesia and Theileria were shown not to form a sister group to the haemosporinids as has been frequently suggested. The data indicate that the biologically diverse family Haemogregarinidae should be divided into at least 3 families (Haemogregarinidae Neveu-Lemaire, 1901, containing the genera Haemogregarina and Cyrilia; Karyolysidae Wenyon, 1926, containing the genus Karyolysus; Hepatozoidae Wenyon, 1926, containing the genus Hepatozoon) because the 4 genera currently within the family do not form a monophyletic group. Correlation between parasite phylogeny and taxonomic affinities of their definitive hosts suggests that the definitive hosts of heteroxenous sporozoa are their ancestral hosts. Heteroxenous sporozoan life cycles apparently have evolved independently to adapt to changes in the feeding behaviors of their definitive hosts.     

Of mice and worms: are co-infections with unrelated parasite strains more damaging to definitive hosts?

Intraspecific competition between co-infecting parasites can influence the amount of virulence, or damage, they do to their host. Kin selection theory dictates that infections with related parasite individuals should have lower virulence than infections with unrelated individuals, because they benefit from inclusive fitness and increased host longevity. These predictions have been tested in a variety of microparasite systems, and in larval stage macroparasites within intermediate hosts, but the influence of adult macroparasite relatedness on virulence has not been investigated in definitive hosts. This study used the human parasite Schistosoma mansoni to determine whether definitive hosts infected with related parasites experience lower virulence than hosts infected with unrelated parasites, and to compare the results from intermediate host studies in this system. The presence of unrelated parasites in an infection decreased parasite infectivity, the ability of a parasite to infect a definitive host, and total worm establishment in hosts, impacting the less virulent parasite strain more severely. Unrelated parasite co-infections had similar virulence to the more virulent of the two parasite strains. We combine these findings with complementary studies of the intermediate snail host and describe trade-offs in virulence and selection within the life cycle. Damage to the host by the dominant strain was muted by the presence of a competitor in the intermediate host, but was largely unaffected in the definitive host. Our results in this host–parasite system suggest that unrelated infections may select for higher virulence in definitive hosts while selecting for lower virulence in intermediate hosts.     

Parasite-induced trophic facilitation exploited by a non-host predator: a manipulator's nightmare

Parasites with complex life cycles, relying on trophic transmission to a definitive host, very often induce changes in the behaviour or appearance of their intermediate hosts. Because this usually makes the intermediate host vulnerable to predation by the definitive host, it is generally assumed that the parasite's transmission rate is increased, and that the modification of the host is, therefore, of great adaptive significance to the parasite. However, in the ecological "real world" other predators unsuitable as hosts may just as well take advantage of the facilitation process and significantly erode the benefit of host manipulation. Here we show that the intertidal New Zealand cockle (Austrovenus stutchburyi), manipulated by its echinostome trematode (Curtuteria australis) to rest on the sediment surface fully exposed to predation from the avian definitive host, is also subject to sublethal predation from a benthic feeding fish (Notolabrus celidotus, Labridae). The fish is targeting only the cockle-foot, in which the parasite preferentially encysts, reducing the infection intensity of manipulated cockles to levels comparable with those in non-manipulated, buried cockles. Based on the frequency and intensity of the foot cropping and predation rates on surfaced cockles by avian hosts, it is estimated that 2.5% of the parasite population in manipulated cockles is transmitted successfully whereas 17.1% is lost to fish. We argue that the adaptive significance of manipulation in the present system depends critically on the feeding behaviour of the definitive host. If cockles constitute the majority of prey items, there will be selection against manipulation. If manipulated cockles are taken as an easily accessible supplement to a diet composed mostly of other prey organisms, behavioural manipulation of the cockle host appears a high risk, high profit transmission strategy. Both these feeding behaviours of birds are known to occur in the field.     

Spatial heterogeneity in recruitment of larval trematodes to snail intermediate hosts

Spatial variation in parasitism is commonly observed in intermediate host populations. However, the factors that determine the causes of this variation remain unclear. Increasing evidence has suggested that spatial heterogeneity in parasitism among intermediate hosts may result from variation in recruitment processes initiated by definitive hosts. I studied the perching and habitat use patterns of wading birds, the definitive hosts in this system, and its consequences for the recruitment of parasites in snail intermediate hosts. Populations of the mangrove snail, Cerithidea scalariformis, collected from mangrove swamps on the east coast of central Florida are parasitized by a diverse community of trematode parasites. These parasites are transmitted from wading birds, which frequently perch on dead mangrove trees. I tested the hypothesis that mangrove perches act as transmission foci for trematode infections of C. scalariformis and that the spatial variation of parasitism frequently observed in this system is likely to emanate from the distribution of wading birds. On this fine spatial scale, definitive host behaviors, responding to a habitat variable, influenced the distribution, abundance and species composition of parasite recruitment to snails. This causal chain of events is supported by regressions between perch density, bird abundance, bird dropping density and ultimately parasite prevalence in snails. Variation between prevalence of parasites in free-ranging snails versus caged snails shows that while avian definitive hosts initiate spatial patterns of parasitism in snails through their perching behaviors, these patterns may be modified by the movement of snail hosts. Snail movement could disperse their associated parasite populations within the marsh, which may potentially homogenize or further increase parasite patchiness initiated by definitive hosts.