Seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus in China

Studies on the seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus from the paddies and ditches in the Dong-ting Lake basin of China, were carried out with samples taken from June 2002 to May 2003. Prevalences were above 21% in all seasons sampled and with a distinct seasonal trend, which was highest (45.81%) in the spring and decreased by degrees. The mean intensity of infection was above 4.0 worms per fish. The maximum intensity of worms recovered from a single fish was 86 in the autumn of 2002. No significant seasonal differences were found in mean intensities, and differences in the mean abundance between winter and spring, winter and autumn were significant. Over-dispersed distributions of P. (N.) celatus in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of P. (N.) celatus showed males between 2.0 mm and 14.0 mm and females between 2.2 mm and 22.2 mm, with the main recruitment phase in the worm populations occurring in the summer and autumn, especially in the autumn, with the lowest recruitment occurring in the winter. The maturation and copulation of worms were mainly focused in the spring season. The sex ratio of female to male was both high in summer (1.09:1) and autumn (1.08:1). The higher proportion of females and the change in the worm sex ratio in summer can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.     

Seasonal population dynamics of Neoechinorhynchus qinghaiensis in the carp, Gymnocypris przewalskii przewalskii, from Qinghai Lake, China

Studies on the seasonal population dynamics of Neoechinorhynchus qinghaiensis (Acanthocephala: Neoechinorhynchidae) in its fish host Gymnocypris przewalskii przewalskii in the Qinghai Lake, China, were carried out with samples taken in May 1991, August 1992, November 1992 and February 1993. Prevalences were higher than 44% in all seasons. The mean intensity of infection was above 124 worms per fish. The maximum intensity of worms recovered from a single fish was 1402 in the autumn of 1992. Differences in the mean abundance, mean intensity and prevalence are not statistically significant relative to season and this is likely to be related to the stable temperatures recorded at the bottom of Qinghai Lake. Over-dispersed distributions of N. qinghaiensis in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of N. qinghaiensis showed males to be less than 3.5 mm and females between 0.5 and 4.25 mm, with the main recruitment phase in the worm populations occurring in the autumn, extending through winter and spring with the lowest recruitment occurring in the summer. The maturation and copulation of worms were mainly focused in the summer season. The sex ratio of female to male was both high in winter (1.51:1) and spring (1.48:1). The higher proportion of females and the change in the worm sex ratio in winter can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.     

The occurrence of Corynosoma strumosum in the grey seal,Halichoerus grypus,caught off the Atlantic coast of Ireland

The occurrence, location and sex ratio of Corynosoma strumosum (Acanthoceophala: Polymorphidae) from 26 juvenile grey seals, Halichoerus grypus, by-caught from around the Inishkea Islands, Co. Mayo, from March to June 1997 were recorded. The location of C. strumosum within the seal did not vary, with all worms being found in the small intestine. The prevalence of infection was 100%, with no other acanthocephalan species being recorded. The mean abundance was 416 (range 80-846) C. strumosum per seal. There was no significant change in abundance by month. The sex ratio of mature female to mature male parasites was 1.2:1. The lengths of female and male worms did not differ significantly.     

Temporal distribution and population structure of two congeneric species of Cucullanus (Nematoda: Cucullanidae) in Orthopristis ruber in Venezuela

The qualitative and quantitative parameters of temporal distribution of Cucullanus tripapillatus and Cucullanus chrysophrydes in the intestine of Orthopristis ruber in the Caribbean Sea on the north of Margarita Island, Venezuela were analysed. A total of 540 fish were collected at random from the catch of commercial trawlers during 1982-83 and 1992-93. Both species of Cucullanus were found throughout the year; prevalence and mean intensity of C. tripapillatus were higher than that of C. chrysophrydes. A significant difference was found in infection between the two years of sampling. Female worms were more abundant than male in both years. Both species exhibited pronounced prevalence and maturity in September and March of each year, indicating seasonality. The patterns of occurrence of the two species of Cucullanus in O. ruber did not change in the 10-year interval but the host size and number of parasites declined, which may be due to over-exploitation of definitive fish hosts.     

Infrapopulations of Procamallanus elatensis Fusco & Overstreet, 1979 (Nematoda: Camallanidae) in the rabbitfish Siganus rivulatus (Teleostei, Siganidae) from the Saudi coast of the Red Sea

Factors regulating gastrointestinal nematode infrapopulations are to a great extent density-dependent. Here, 23 natural infrapopulations (41-281 individuals) of the viviparous nematode Procamallanus elatensis (Camallanidae) from the fish Siganus rivulatus were found distributed in a well-defined fundamental niche (posterior 55% of the intestine). Immature worms were mostly found in the anterior third of this niche, while mature worms were found in aggregations posterior to them and followed by gravid females in the posterior 20% of the intestine. This distribution strongly suggests that worms migrate towards the posterior intestine while they mature, copulate and reproduce. In small infrapopulations, the sex ratios were distinctly female-biased and the number of gravid females was low. In large infrapopulations, the sex ratios were distinctly male-biased and the number of gravid females was high. However, the mean lengths of both immature males and females and mature females decreased dramatically as the infrapopulation size increased, while those of mature males increased significantly. These results strongly suggest intraspecific competition and density-dependent regulation of mean worm length, and the increase in the mean length of mature males strongly suggests intense sexual selection and competition between mature males. Production of larvae by female worms decreased significantly as the infrapopulation size increased, suggesting a density-dependent reduction in female worm fertility. The results are statistically significant and strongly suggest that infrapopulation self-regulation is through density-dependent mechanisms, in which development of immature worms, infrapopulation size, sex ratio, sexual selection and carrying capacity of the fundamental niche play essential roles in shaping and regulating the infrapopulations.     

A population study of the metastrongylid nematode Skrjabingylus nasicola in the weasel Mustela nivalis

Analyses of adult worms of Skrjabingylus nasicola occurring in the nasal sinuses of the weasel Mustela nivalis from three localities in the British Isles show that the intensity of infestation can be correlated with increasing severity of skull damage, which in turn increases as the weasel ages. It is suggested that, apart from hormonal differences, the smaller sized female skull is likely to be linked with lower levels of infestation in female compared with male weasels. Also a reduction in mean worm length in female skulls and in heavy infestations of S. nasicola is probably the result of a "crowding effect", previously described for other helminth infections in the definitive host. Crowding appears to have no effect on the sex ratio of worm populations, although there is a tendency for the ratio of female: male worms to increase in female weasels. Reasons for this are discussed.     

Reproductive traits of the acanthocephalan Neoechinorhynchus brentnickoli in the definitive host

The Acanthocephala constitute a group of helminth parasites that, as adults, infect all classes of vertebrates. Adults of Neoechinorhynchus brentnickoli are parasites of Dormitator latifrons, a commercially important fish species in Tres Palos Lagoon, Guerrero, Mexico. The aim of this study was to describe features of the reproductive biology of this acanthocephalan. Fish were collected from Laguna de Tres Palos during February 2012 to February 2013. The number of fish that were examined (n=688) ranged from 35 (June) to 70 (August) in each collection. The prevalence of infection was more than 90% during this period and mean abundance varied significantly from 32.3 worms per fish (July 2012) to 89.3 worms per fish (March 2012). Acanthocephalans were reproductively active during the whole year. The stomach was the region of the digestive tract with the smallest percentage of helminths, and females were more abundant than males in all sections of the intestine. Larger male and female worms were always located in the more posterior sections of the digestive tract. The mean length at which 50% of individuals reached sexual maturity was 2.9 mm for females and 2.3 mm for males. Relative fecundity increased with length in females.     

The reproductive biology of Scyliorhinus canicula in the Bristol Channel, U.K.

Among 972 Scyliorhinus canicula , the overall sex ratio (males:females) was 1:1·23. Males matured between 490 and 540 mm L _T with 50% maturity at 520 mm. Females matured between 520 and 640 mm L _T with 50% maturity at 550 mm. Female gonadosomatic index peaked in May. Fecundity increased with fish length. The egg laying season lasted 10 months with a peak in June and July. The importance of erect, sessile invertebrates such as bryozoans, poriferans and hydroids as egg-case deposition sites has been established. Recently hatched fish were born in an equal sex ratio and at a mean length of 100·5 mm and mean weight of 3·07 g. One intersexual fish is described.     

Nematode lungworms of two species of anuran amphibians: evidence for co-adaptation

Genetic studies have indicated that some parasite species formerly thought to be generalists are complexes of morphologically similar species, each appearing to specialize on different host species. Studies on such species are needed to obtain ecological and parasitological data to address whether there are fitness costs in parasitizing atypical host species. We examined whether lungworms from two anuran host species, Lithobates sylvaticus and Lithobates pipiens, differed in measures of infection success in L. pipiens recipient hosts. We also determined if the worms from the two host species were sources of genetically resolvable species of morphologically similar nematodes. Sequences of internal transcribed spacer and lsrDNA regions of adult lungworms from each host species indicated that worms from L. sylvaticus matched Rhabdias bakeri, whereas worms from L. pipiens matched Rhabdias ranae. Our work suggested that these morphologically similar species are distant non-sibling taxa. We infected male and female metamorphs experimentally with lungworm larvae of the two species. We observed higher penetration, higher prevalence and higher mean abundance of adult worms in lungs of male and female metamorphs exposed to R. ranae larvae than in lungs of metamorphs exposed to R. bakeri larvae. Furthermore, metamorphs exposed to R. ranae larvae carried larger adult female worms in their lungs. Some variation in infection measures depended on host sex, but only for one parasite species considered. Overall, the differential establishment and reproductive potential of R. ranae and R. bakeri in L. pipiens suggests co-adaptation.     

长江黄州江段长须黄颡鱼肠道内寄生棘头虫的生态研究

解剖检查了 133尾捕自长江黄州江段的长须黄颡鱼 ,发现寄主感染长江丽棘虫的感染率为 4 8.9% ,感染强度为 5 .4 (虫 /尾 ) ,平均密度为 2 .6 (虫 /尾 ) ,感染鲇异棘虫的感染率为 2 1.8% ,感染强度为 5 .5 (虫 /尾 ) ,平均密度为1.2 (虫 /尾 ) ,两种棘头虫在长须黄颡鱼种群中均为聚集分布 ;当两种棘头虫共同寄生在宿主肠道内时 ,其感染强度和单独感染时相比没有显著差异 ,但是 ,各自的生态位宽度均变小 ;两种棘头虫的正关联关系显著。     

Relationship between helminth parasites and demographic attributes of a population of the subterranean rodent Ctenomys talarum (Rodentla: Octodontidae)

The helminth parasite fauna of a natural population of the octodontid, Ctenomys talarum, was studied. Parasites that were found included the nematodes Heligmostrongylus sp. and Trichuris sp. Total prevalence of parasitism was 92.3%, mean intensity of infection was 22.7 worms, and mean abundance was 21 worms. Prevalence and mean abundance of infection with Heligmostrongylus sp. were higher in C. talarum males relative to females. Ecological and physiological causes, as well as the mating system of the host species, influence the likelihood of sex differences in parasite infection. The low parasite burden and diversity of C. talarum are associated with restrictions imposed by the subterranean habitat and with life-history traits of these rodents. Whether these findings apply to other Ctenomys spp. is unknown.     

The life cycle and seasonal changes in the occurrence of Pomphorhynchus laevis (Palaeacanthocephala, Pomphorhynchidae) in a small isolated lake

In a small isolated lake in Slovakia, the fish acanthocephalan Pomphorhynchus laevis using Gammarus balcanicus and the minnow Phoxinus phoxinus, respectively, as its intermediate and final hosts, represented a dominant helminth species. Its prevalence and intensity of infection in fish showed no significant variation during a year fluctuating above the mean values of 89% and 6.6 worms per fish. The mean prevalence of P. laevis larvae in Gammarus was 41.4% with a maximum in the late summer and autumn; individual crustaceans were infected by 1-9 larvae. There was one generation of P. laevis per year. Following up an annual cycle, an occurrence of new infections of Gammarus culminated in October and in the next May for Phoxinus. The sex ratios of both the adults and larvae of acanthocephalans were near unity but favoured slightly males in spring and autumn. The distribution of P. laevis in minnows and crustaceans was highly aggregated and fitted with the negative binomial model. The spatial distribution analysis of parasites along the fish alimentary tract showed a clear preference of P. laevis for its proximal half, with the maximum numbers in the site of the first intestinal loop. Immature worms of both sexes predominated in the proximal region and moved slightly down the alimentary tract during their growth and maturation.     

Geographical distribution of Metagonimus yokogawai and M. miyatai in Shizuoka Prefecture, Japan, and their site preferences in the sweetfish, Plecoglossus altivelis, and hamsters

Sweetfish, Plecoglossus altivelis, obtained from 18 rivers in Shizuoka Prefecture were examined for metacercarial infection of 2 flukes, Metagonimus yokogawai and Metagonimus miyatai. The infection rate and density of metacercariae in the fish were higher in eastern and western regions than in central region of the prefecture. After infection of hamsters with metacercariae derived from the scale, 98.7% of the adult worms obtained from the intestine was found to be M. miyatai. Conversely, from infection with metacercariae from the flesh, 90.0% of the worms was M. yokogawai. Since the worms had no exclusivity in the tissues, we conclude that the flukes have location preference with the former primarily preferring the scale, and the latter the flesh. Fish from two rivers located in adjacent areas in the western region had relatively a higher ratio of M. yokogawai in the scale relative to other rivers, suggesting an intraspecific genetic variation due to geographical isolation. On examination of adult worms in the hamster's intestine, M. yokogawai was mainly located towards the anterior part of the intestine, unlike M. miyatai, suggesting that in mammalian host too, the parasites have site preference.     

Chronic calorie restriction increases susceptibility of laboratory mice (Mus musculus) to a primary intestinal parasite infection

Long-term calorie restriction (CR) has numerous benefits; however, effects of CR on susceptibility to intact pathogens are not well understood. Because CR enhances immune function of laboratory mice ( Mus musculus ), it was hypothesized that mice subjected to CR would be less susceptible to experimental infections of the intestinal parasite Heligmosomoides bakeri . Furthermore, because H. bakeri must combat a greater host immune response by CR mice compared to fully fed mice, it also was also hypothesized that (i) worms living in CR hosts would have lower reproduction than worms from ad libitum -fed mice, and (ii) CR mice would have a more female-biased sex ratio as male worms may be more vulnerable to host immune response than female worms. Mice were subjected to CR for 6.7 months and were then infected with H. bakeri for one additional month. As expected, CR mice had equal or enhanced immune response (eosinophils and immunoglobin G1 production) to H. bakeri infection compared to ad libitum -fed mice, and CR mice harbored a more female-biased sex ratio than ad libitum -fed mice. Contrary to predictions, CR mice had more worms than ad libitum -fed mice and the worms from CR mice produced more eggs than worms from ad libitum -fed mice. These data indicate that, despite the evidence that long-term CR enhances traditional measures of immune function, CR may actually increase susceptibility to intact parasite infection. Furthermore, changes in worm reproduction and differential survival of male vs. female worms may influence host–parasite transmission dynamics during long-term host CR.     

中国南部池养幼鲩寄生鱊头槽绦虫的种群动态

本项目研究池塘养殖的鲩 (草 )鱼体内寄生的头槽绦虫 (B .acheilognathi)的种群动态。于 1 986、1 9 87和 1 998三年内分别观察 0、Ⅰ龄幼鲩及Ⅱ龄商品鲩感染的情况。 0龄及Ⅰ龄越冬鲩的绦虫种群由初染至收敛周期为 1年 ,Ⅱ龄鲩不感染 ,冬季高感染率导致早春水温在 2 0 4℃的感染高峰 ,感染强度持续数月 ,6月达到 2 4 3虫 /鱼。未感染的 0及Ⅰ龄幼鲩在 2、 3月分别引进放养感染了的越冬Ⅰ龄鲩的池塘。1个月后 ,感染率达到 93 1 %～ 96 9% ,8至 9月感染率迅速下降 ,1 0月又稍升高。 1 986和 1 987年的 4～8月 ,绦虫的分布 (S2 / X) >1 ,为聚集分布 ,体长 <1cm的幼虫在种群结构中占优势 ,为 97 2 %～98 2 % ,1 1月幼虫数目下降 ,大孕节绦虫随之出现 ,1 2月大孕节绦虫仅少数存留或全部消失。试验结果为消灭鲩鱼绦虫病提供了可靠依据。     

Population and infection dynamics of Daubaylia potomaca (Nematoda: Rhabditida) in Helisoma anceps

Daubaylia potomaca is an unusual parasite for several reasons. Specifically, it has a direct life cycle in which it uses a planorbid snail, Helisoma anceps , as the definitive host. In addition, adult females have been shown to be both the infective stage and the only stage documented to be shed from a live, infected host. Finally, adults, juveniles, and eggs have been observed in all tissues and blood spaces of the host, suggesting the parasite consumes and actively migrates through host tissue. The present study examined the population and infection dynamics of D. potomaca in Mallard Lake, a 4.9-ha public access pond in the Piedmont region of North Carolina. In particular, the study examined the role of seasonality on the prevalence and mean intensity of infection of D. potomaca in the snail host. Data collected from August 2008 to October 2009 suggest that prevalence and mean intensity were inversely related in the spring and fall. Prevalence in fall 2008 was 10.3% but increased to 47.3% in spring 2009. Conversely, intensity was high in fall 2008 at 52.4 ± 8.9 worms/infected host but dropped to 3.1 ± 0.3 worms/infected host in spring 2009. During the same time, the parasites within the snails went from highly aggregated populations in the fall to a less aggregated distribution in the spring. It is hypothesized that D. potomaca induces mortality of the snail hosts during the winter, followed by a rapid recruitment event of the nematodes by the snail population after torpor.     

Prevalence and intensity ofCapillaria catostomi (Nematoda: Trichuroidea) in white sucker (Catostomus commersoni) in southern Lake Huron,Canada

Synopsis A total of 314 white suckers (Catostomus commersoni) taken monthly during May to December 1975 and in April and May 1976 from southern Lake Huron, Ontario, Canada, were examined forCapillaria catostomi.Prevalence determined from fresh white suckers (66%) was significantly lower than from frozen white suckers (81%). However, there was no significant difference in prevalence ofC. catostomi in samples taken at monthly intervals; in male and female white suckers; or in the age categories.Mean intensity of infection was not significantly different in fresh (9.6 [± 13.41]) or frozen (10.4 [± 13.11]) white suckers. There was no significant difference in intensities between monthly samples in male and female white suckers or in the age categories. Suckers were infected with 1–172 worms. The percentage of male, female and immature worms did not change with sex or age of host or by month. The frequency distribution showed the parasites were overdispersed.A possible life cycle forC. catostomi involving an oligochaete intermediate host is discussed and an attempt made to explain the almost constant levels of prevalence and intensity.     

Toxocara cati infections in stray cats in northern Iran

A cross-sectional survey was undertaken to study the prevalence and intensity of infection with Toxocara cati in 100 stray cats, from April to October 2004 in urban areas of Sari, northern Iran. A total of 44 cats (44%) were found to be infected with T. cati. There was a significant difference in the prevalence of infection relative to host age and weight (P = 0.000). There was also a significant difference in the intensity of infection relative to body weight and urban sites (P < 0.05). No significant difference was found between the prevalence of infection relative to host gender, urban sites and season (P>0.05), nor in the intensity of infection between host gender, age and season (P>0.05). The intensity of infection ranged from 1 to 32 worms per cat, with a mean of 7.30 +/- 6.82.     

Occurrence and maturation of Rhabdochona gnedini (Nematoda: Rhabdochonidae) in the barbels of the Sousa River, Portugal

Data on the seasonal occurrence and maturation of Rhabdochona gnedini Skrjabin, 1946 in its definitive host, the barbel Barbus bocagei, from the Sousa River, in northern Portugal, are presented. Monthly samples were taken from November, 1998 to October, 1999. A total of 178 fish specimens were inspected. R. gnedini occurred with high prevalences during whole year, attaining the highest values of intensity in summer (overall prevalence and mean intensity 85% and 31, respectively). A clear annual cycle of maturation was observed; females with mature eggs occurred in spring and summer. Unidentified Rhabdochona larvae were recorded from the trichopteran larvae Hydropsyche sp. (prevalence and intensity 29% and one to 34, respectively). These larvae are presumptive intermediate host for R. gnedini.