Experimental exposure of Helisoma trivolvis and Biomphalaria glabrata (Gastropoda) to Ribeiroia ondatrae (Trematoda)

Experimental infections provide an important foundation for understanding host responses to parasites. While infections with Ribeiroia ondatrae cause mortality and malformations in a wide range of amphibian second intermediate host species, little is known about how the parasite affects its snail first intermediate hosts or even what species can support infection. In this study, we experimentally exposed Helisoma trivolvis, a commonly reported host of R. ondatrae, and Biomphalaria glabrata, a confamilial snail known to host Ribeiroia marini, to increasing concentrations of embryonated eggs of R. ondatrae obtained from surrogate definitive hosts. Over the course of 8 wk, we examined the effect of parasite exposure on infection status, time-to-cercariae release, host size, and mortality of both snail species. Helisoma trivolvis was a highly competent host for R. ondatrae infection, with over 93% infection in all exposed snails, regardless of egg exposure level. However, no infections were detected among exposed B. glabrata, despite previous accounts of this snail hosting a congener parasite. Among exposed H. trivolvis, high parasite exposure reduced growth, decreased time-to-cercariae release, and caused marginally significant increases in mortality. Interestingly, while B. glabrata snails did not become infected with R. ondatrae, individuals exposed to 650 R. ondatrae eggs grew less rapidly than unexposed snails, suggesting a sub-lethal energetic cost associated with parasite exposure. Our results highlight the importance of using experimental infections to understand the effects of parasite exposure on host- and non-host species, each of which can be affected by exposure.     

Fascioloides magna (Bassi, 1875) in feral swine from southern Texas.

Between 1971 and 1975, Fascioloides magna was found in 46 of 67 (69%) feral swine (Sus scrofa) in southern Texas. Flukes were recovered from swine in areas where F. magna commonly has been recovered from white-tailed deer and cattle. One to 12 flukes were recovered from each infected animal. Their presence was indicated by black hematin pigment on the liver and various other internal organs. Eggs were not detected in the gallbladder or feces of infected animals although mature flukes and eggs were recovered in the livers suggesting that, like cattle, feral swine can be infected but are aberrant hosts for the parasite and do not disseminate eggs.     

Strength in numbers: high parasite burdens increase transmission of a protozoan parasite of monarch butterflies (<Emphasis Type="Italic">Danaus plexippus</Emphasis>)

Parasites often produce large numbers of offspring within their hosts. High parasite burdens are thought to be important for parasite transmission, but can also lower host fitness. We studied the protozoan Ophryocystis elektroscirrha, a common parasite of monarch butterflies (Danaus plexippus), to quantify the benefits of high parasite burdens for parasite transmission. This parasite is transmitted vertically when females scatter spores onto eggs and host plant leaves during oviposition; spores can also be transmitted between mating adults. Monarch larvae were experimentally infected and emerging adult females were mated and monitored in individual outdoor field cages. We provided females with fresh host plant material daily and quantified their lifespan and lifetime fecundity. Parasite transmission was measured by counting the numbers of parasite spores transferred to eggs and host plant leaves. We also quantified spores transferred from infected females to their mating partners. Infected monarchs had shorter lifespans and lower lifetime fecundity than uninfected monarchs. Among infected females, those with higher parasite loads transmitted more parasite spores to their eggs and to host plant leaves. There was also a trend for females with greater parasite loads to transmit more spores to their mating partners. These results demonstrate that high parasite loads on infected butterflies confer a strong fitness advantage to the parasite by increasing between-host transmission.     

Lung lesions in an opossum (Didelphis virginiana) associated with Capillaria didelphis

An opossum (Didelphis virginiana) live-trapped on Parramore Island, Virginia was infected with the lung parasite Capillaria didelphis. Lung lesions associated with this parasite were extensive and consisted of numerous areas with central necrosis deep within the parenchyma. Necrotic foci were present around airways and consisted of a mixture of inflammatory cells and cellular debris, adult nematodes and many bipolar eggs. This parasite causes severe verminous pneumonia in the opossum.     

The role of Callionymus lyra and C. reticulates in the life cycle of Lernaeocera lusci in Belgian coastal waters (Southern Bight of the North Sea)

A survey of the dragonet Callionymus lyra and the reticulated dragonet C. reticulatus from Belgian coastal waters (Southern Bight of the North Sea) in June 1991 revealed 34% of dragonets infected with 1–7 Lernaeocera lusci. This same parasite infected 9% of the reticulated dragonets (mean intensity =1). Parasite size is host-size-dependent. Of the parasites collected from C, lyra 64% were gravid adults (substage X), and a significant positive relationship between the number of eggs and axial length of the parasite was found. The parasites were overdispersed within the dragonet population ( s ²/ m =1.67)     

Plagiorchis elegans (Digenea: Plagiorchiidae) infections in Stagnicola elodes (Pulmonata: Lymnaeidae): host susceptibility, growth, reproduction, mortality, and cercarial production.

Eggs of Plagiorchis elegans were readily ingested by Stagnicola elodes of all ages, but were more infective to immature than mature snails. Infection enhanced the growth of the host in a dose-dependent manner. The number of cercariae released by immature snails increased with the age of the snail host; mature snails yielded fewer cercariae. Heavily infected snails tended to die prematurely, thereby reducing their total production of cercariae to levels below those of more lightly infected individuals. Even light infections castrated the snail host. Snails that acquired the infection as juveniles never produced eggs. Actively reproducing snails ceased egg laying within days of infection and never recovered. All parasite effects on the growth and reproduction of the snail host first manifested themselves during the early stages of infection, long before the development of daughter sporocysts and cercariae, and are therefore attributable to the effects of mother sporocysts. The study provides insight into how this natural enemy of mosquito larvae may be established in natural snail populations by means of strategically timed introductions of parasite eggs, with a goal of maximizing cercarial production for the biological control of sympatric mosquito larvae.     

Animal Models for Echinostoma malayanum Infection: Worm Recovery and Some Pathology

Echinostomes are intestinal trematodes that infect a wide range of vertebrate hosts, including humans, in their adult stage and also parasitize numerous invertebrate and cold-blooded vertebrate hosts in their larval stages. The purpose of this study was to compare Echinostoma malayanum parasite growth, including worm recovery, body size of adult worms, eggs per worm, eggs per gram of feces, and pathological changes in the small intestine of experimental animals. In this study, 6-8-week-old male hamsters, rats, mice, and gerbils were infected with echinostome metacercariae and then sacrificed at day 60 post-infection. The small intestine and feces of each infected animal were collected and then processed for analysis. The results showed that worm recovery, eggs per worm, and eggs per gram of feces from all infected hamsters were higher compared with infected rats and mice. However, in infected gerbils, no parasites were observed in the small intestine, and there were no parasite eggs in the feces. The volume of eggs per gram of feces and eggs per worm were related to parasite size. The results of histopathological changes in the small intestine of infected groups showed abnormal villi and goblet cells, as evidenced by short villi and an increase in the number and size of goblet cells compared with the normal control group.     

Spontaneous occurrence of Angiostrongylus costaricensis in marmosets (Saguinus mystax)

Two marmosets imported from Iquitos, Peru, were found to be infected with Angiostrongylus costaricensis. Both animals had large solitary granulomas involving the wall and adjacent mesentery of the small intestine. Histopathologic examination showed the adult nematodes in the lumina of the mesenteric arteries that coursed through these granulomas. The inflammatory reaction was associated with numerous degenerating eggs and larvae. This is the first report of this parasite in nonhuman primates and extends its geographic range to Peru. In addition, in one animal, Dipetalonema sp were seen free in the abdominal cavity, and pleroceroid larvae (spargana) were in the loose connective tissue of the left axilla. This animal also had microgranulomas associated with eggs and larvae of Angiostrongylus in the kidney, liver, lung, and heart.     

Fluke (Spirorchiidae) infections in sea turtles stranded on Taiwan: prevalence and pathology

The prevalence of spirorchiid fluke infections of marine turtles is high and may cause the death of the hosts throughout their ranges. Virtually nothing has been reported regarding the infective status of sea turtles stranded on Taiwan. Between 2007 and 2010, 30 green turtles (Chelonia mydas) and 2 loggerhead turtles ( Caretta caretta ), stranded and dead, were examined for spirorchiid flukes and their eggs. Twenty-four of the green turtles were juveniles, and the stranded loggerhead turtles were subadults. Adult spirorchiid flukes were found in 13 green turtles but not in the loggerheads. Four species of flukes were identified, namely, Leardius learedi , Hapalotrema postorchis , H. mehrai , and Carettacola hawaiiensis . The main infection sites were the major arteries and heart. Seventy percent of the green turtles harbored spirorchiid eggs, but no eggs were found in loggerheads. The largest eggs with bipolar spines, type I eggs, were found in every case. Although more than half of the stranded turtles were infected, parasite infections were not the main cause of death in the green turtles. Fishery by-catch is probably responsible for the mortality of these stranded turtles.     

Coprologic survey of parasites of spotted hyenas (Crocuta crocuta) in the Masai Mara National Reserve,Kenya

Seventy fecal samples from spotted hyenas (Crocuta crocuta) in the Masai Mara National Reserve, Kenya were examined for parasite eggs and oocysts using sugar flotation. A total of nine parasite genera were identified, and all samples were positive for at least one parasite species. Most individuals were infected with Ancylostoma sp. and Spirometra sp., and these species had the highest median intensity of infection. Other parasites identified include Isospora sp., Taeniidae, Spirurida, Toxocara sp., Mesocestoides sp., Dipylidium sp., and Trichuris sp.     

Reproductive Strategies of the Insidious Fish Ectoparasite,Neobenedenia sp. (Capsalidae: Monogenea)

Fish monogeneans are lethal parasites in aquaculture. We provide the first experimental evidence that a notorious fish monogenean, Neobenedenia sp., can produce viable eggs in isolation for three consecutive generations. We infected individual, isolated, farmed barramundi, Lates calcarifer (Bloch) with a single oncomiracidium (larva) of the hermaphroditic monogenean Neobenedenia sp. Isolated parasites reached sexual maturity at day 10 post-hatch (24°C, 35‰) and laid ∼3,300 embryonated eggs over 17 days. Egg production rapidly increased following sexually maturity on day 10 (58±15 eggs) and peaked on day 15 (496±68 eggs) before gradually decreasing. Neobenedenia sp. exhibited egg laying and egg hatching rhythms. Parasites laid eggs continuously, but egg production increased in periods of darkness (64.3%), while the majority of oncomiracidia (81%) emerged from eggs in the first three hours of light. Eggs laid by isolated ‘parent’ parasites hatched and individual emerging oncomiracidia were used to infect more individual, isolated fish, with three consecutive, isolated, parasite generations (F1, F2 and F3) raised in the laboratory. Infection success and egg hatching success did not differ between generations. Our data show that one parasite, in the absence of a mate, presents a severe threat to captive fish populations.     

The occurrence of gapeworm (Syngamus trachea) in willow grouse.

21.4% of the willow grouse (Lagopus lagopus) examined from a coastal locality in northern Norway were infected with Syngamus trachea. None of the willow grouse examined from an inland locality with colder and longer winters were infected with the parasite. It is suggested that the parasite may influence survival of the grouse population.     

Blood platelets and schistosome egg excretion

The eggs of helminths of the Schistosoma genus require to be extravasated in order to continue the life cycle of the parasite. The possible mode by which this takes place was investigated in a mouse model. Suppression of platelet activity in Schistosoma mansoni-infected mice by administering rabbit anti-mouse platelet serum or a selection of "antiplatelet drugs" resulted in a significant reduction of parasite egg excretion. This reduction was best achieved when antiplatelet agents were administered just before the onset of parasite egg excretion. The association between parasite eggs and platelets was illustrated in vivo and in vitro where platelet aggregates on egg surfaces were seen in both light and electron microscopy. In addition, eggs that had been isolated from infected mouse tissues induced platelet aggregation in whole mouse blood, and this was inhibited by preincubation with the beta-lactam antibiotic, ticarcillin. Isolated eggs were also capable of inducing ex vivo platelet aggregation in mice, which was dependent on presensitization with eggs. These data suggest a role for platelets in the extravasation and excretion of parasite eggs in schistosomiasis.     

Experimental heteroxenous cycle of Lagochilascaris minor Leiper, 1909 (Nematoda: Ascarididae) in white mice and in cats.

Reports of natural infections of sylvatic carnivores by adult worms of species similar to Lagochilascaris minor in the Neotropical region led to attempts to establish experimental cycles in laboratory mice and in cats. Also, larval development was seen in the skeletal muscle of an agouti (Dasyprocta leporina) infected per os with incubated eggs of the parasite obtained from a human case. In cats, adult worms develop and fertile eggs are expelled in the feces; in mice, larval stages of the parasite develop, and are encapsulate in the skeletal muscle, and in the adipose and subcutaneous connective tissue. From our observations, we conclude that the larva infective for the mouse is the early 3rd stage, while for the final host the infective form is the later 3rd stage. A single moult was seen in the mouse, giving rise to a small population of 4th stage larvae, long after the initial infection.     

Increased prevalence of larval Eustronglylides (Nematoda) in the mummichog, Fundulus heteroclitus (L.), from the discharge canal of a power plant in the Chesapeake Bay

The prevalence of larval Eustrongylides sp. in the mummichog, Fundulus heteroclitus , was compared for two populations, one in the vicinity of the intake and one in the discharge canal of a power plant at Chalk Point on the Patuxent River, Maryland. The parasite was four times as prevalent in female F. heteroclitus collected from the discharge canal as in those collected from the intake area. Almost all infected fish were 70 mm or greater in total length. The larvae occurred in capsules and free in the mesentery, or associated with the gut, liver, or gonad of the host; multiple infections were common. Infection by Eustrongylides resulted in pronounced negative effects on F. heteroclitus . The dry weight of somatic tissue was reduced 5% and ovary dry weight was reduced 50% in infected individuals, compared to uninfected individuals of the same length. The proportion of infected females carrying ripe eggs during the breeding season was less than half the value for uninfected females. It is hypothesized that the greater prevalence of the parasite in the discharge canal results from increased abundances of oligochaetes (suspected first intermediate hosts of the parasite), presumably as a consequence of elevated temperatures and organic enrichment from the power plant.     

Alternative development in Polystoma gallieni (Platyhelminthes,Monogenea) and life cycle evolution

Considering the addition of intermediate transmission steps during life cycle evolution, developmental plasticity, canalization forces and inherited parental effect must be invoked to explain new host colonization. Unfortunately, there is a lack of experimental procedures and relevant models to explore the adaptive value of alternative developmental phenotypes during life cycle evolution. However, within the monogeneans that are characterized by a direct life cycle, an extension of the transmission strategy of amphibian parasites has been reported within species of Polystoma and Metapolystoma (Polyopisthocotylea; Polystomatidae). In this study, we tested whether the infection success of Polystoma gallieni within tadpoles of its specific host, the Stripeless Tree Frog Hyla meridionalis, differs depending on the parental origin of the oncomiracidium. An increase in the infection success of the parasitic larvae when exposed to the same experimental conditions as their parents was expected as an adaptive pattern of non-genetic inherited information. Twice as many parasites were actually recorded from tadpoles infected with oncomiracidia hatching from eggs of the bladder parental phenotype (1.63 ± 0.82 parasites per host) than from tadpoles infected with oncomiracidia hatching from eggs of the branchial parental phenotype (0.83 ± 0.64 parasites per host). Because in natural environments the alternation of the two phenotypes is likely to occur due to the ecology of its host, the differential infection success within young tadpoles could have an adaptive value that favors the parasite transmission over time.     

Observations on myiasis by the calliphorid,Bufolucilia silvarum,in the eastern American toad (Bufo americanus americanus) from southeastern Wisconsin

Larvae of certain species of blowflies (Calliphoridae) cause myiasis in amphibians which may result in significant mortality, yet there are few reports from North America. In this study, we observed primary myiasis in a population of juvenile eastern American toads (Bufo americanus americanus) collected during May-July 1998 from southeastern Wisconsin (USA). Nine (6%) of 140 toads were infected by the green blow fly (Bufolucilia silvarum) with a mean intensity of 10.5 +/- 7.2 (range = 1-24). Weekly parasite prevalence and mean intensity remained low, ranging from 0-20% and 2 +/- 1.4 to 14 +/- 6, respectively. We found: 1) flies lay eggs on healthy toads, 2) eggs hatch with first instar maggots penetrating under the skin, 3) maggots develop to mature third instars within 5-7 days, 4) maggots leave the host and form pupa within 8-11 days of hatching, and 5) maggots pupate within 7-9 days at room temperature. All infected toads died within 1-2 wk as a result of the infection. The low prevalence observed in this study and other reports of this species from mammalian and bird carcasses indicated that B. silvarum is probably a facultative parasite of toads and other amphibians in the United States. This is the first report of B. silvarum causing myiasis in Wisconsin amphibians and the first report in eastern American toads in the United States.     

Helminth parasites of unisexual and bisexual whiptail lizards (Teiidae) in North America. V. Mesocestoides sp. tetrathyridia (Cestoidea: Cyclophyllidea) from four species of Cnemidophorus

Two hundred and one whiptail lizards, Cnemidophorus spp., from Texas and Colorado (USA), were examined for Mesocestoides sp. tetrathyridia. Eleven (5%) were infected, including three of 58 (5%) C. dixoni, six of 70 (9%) C. gularis septemvittatus, one of 35 (3%) C. marmoratus, and one of 34 (3%) C. tesselatus; four C. inornatus heptagrammus were not infected. In addition, 41 non-cnemidophorine lizards from the same study area were not infected. Free tetrathyridia were found in the body cavity of lizards and encapsulated tetrathyridia were observed in the heart, liver, stomach, mesenteries, ovaries, intestines, and lungs. None of the Mesocestoides sp. exhibited any evidence of asexual proliferation such as multiple scoleces or buds. This note, the fifth in a series of reports on helminths of Cnemidophorus spp., represents the first time Mesocestoides sp. has been reported from these four taxa, and Colorado is a new geographic locality record for this parasite.     

The importance of the opossum (Didelphis albiventris) as a reservoir for Trypanosoma cruzi in Bambuí, Minas Gerais State.

In a survey realized on the sylvatic and peridomestic environments at Bambuí county, Minas Gerais State, 44 (37.9%) out of 116 opossums (Didelphis albiventris) captured were found to be naturally infected with Trypanosoma cruzi. One hundred and forty three parasite samples were obtained from 43 infected opossums using simultaneously hemoculture, xenodiagnosis (Triatoma infestans, Panstrongylus megistus and Rhodnius neglectus) and examination of anal glands contents. The parasite samples were characterized according to six isoenzyme patterns. All samples, independently of the method of isolation, presented an isoenzyme pattern similar to the standard T. cruzi Z1, showing that either xenodiagnosis or hemoculture can used without selecting parasite subpopulation from naturally infected opossums. Previous isoenzyme patterns reported for human T. cruzi isolates from the same region were completely different. This isoenzyme dissimilarity between sylvatic and domiciliar environments suggests the existence of two independent T. cruzi transmission cycles in Bambuí. The epidemiological implications of these results are discussed.     

Modification of the pathogenicity of Schistosoma mattheei for sheep by passage of the parasite in hamsters

Border Leicester X Suffolk sheep infected with a strain of S. mattheei maintained in hamsters do not develop the same pathological changes as Romney Marsh sheep infected with the same strain of parasite before hamster passage. To determine the cause of this reduced pathogenicity, five Romney Marsh sheep were each infected with 10 000 cercariae of the hamster-passaged parasite and five with 10 000 cercariae of a S. mattheei strain from Onderstepoort, South Africa, passaged exclusively through sheep. Striking pathological and parasitological differences were found between the two strains. Infection with the "sheep" strain was lethal, whereas infection with the "hamster" strain produced little evidence of clinical disease. By 13 weeks post-infection the mean body weight of the sheep infected with the sheep strain had declined by 15% compared with both the uninfected controls and the sheep infected with the hamster strain, and the mean PCV was lowered to 20% in the sheep strain infected animals. Egg production began at seven weeks with the sheep strain, faecal counts rising to more than 300 e.p.g., whereas only two of the sheep infected with the hamster strain passed eggs in the faeces (at nine weeks) and the maximum egg count was 50 e.p.g. Twice as many adult worms of the sheep strain were recovered, and, although the number of eggs found in the tissues "per worm pair" was not significantly different, overall egg production was higher for the sheep strain; also more of the sheep strain eggs were deposited in the intestines. Similar parasite differences were seen in a supplementary study in mice and it seemed that "attenuation" of the parasite had occurred, presumably due to its maintenance in hamsters. Histopathological observations and faecal egg counts both indicated an inability of hamster strain eggs to penetrate the intestinal lumen; this was probably important in reducing the pathogenicity of the hamster strain.