Distribution Patterns Of Parasites Research Articles

Molecular Survey and Microscopic Examination of Haemoparasites Infecting Lizards from Morocco.

Understanding the factors influencing parasite diversification, their distribution and infection patterns among hosts provides valuable information on the impact of parasitism on natural populations and the dynamics and evolution of disease outbreaks. In this study, we investigated prevalence and intensity of infection by blood parasites, the diversity, distribution, host specificity and infection patterns of apicomplexan parasites in lizards of Morocco. Samples from lizard specimens were collected between 2019 and 2021 from different prospected localities in Morocco. In total, 1500 lizards were collected, and their blood and tail tips were screened for blood parasites. Using a PCR approach, we detected two distinct apicomplexan parasite groups (haemogregarines and haemococcidians) and also Stramenopiles (Proteromonas). A significant difference was identified between hosts families, with no agamids or skinks infected and with particularly high infection rates in lacertids. Twenty-four samples were sequenced and included in a phylogenetic assessment. Two samples of Atlantolacerta andreanskyi were infected with unidentified species of Proteromonas. Three samples were infected with haemococcidians, including two samples with Schellackia and another sample with Lankesterella, more closely related to others isolated from bird hosts. These are the first reports of Lankesterella and Proteromonas in these lizards from Morocco. Nineteen different isolates of the complex of Hepatozoon/Karyolysus were identical or very similar to previously sequenced parasites from North Africa and Iberian Peninsula and included new host species. Our results highlight the need for future research on the vectors involved in transmission that may influence the ecology and distribution patterns of these parasites. Given that Morocco is a hot spot of endemicity and reptile richness, our results are relevant not only in the context of their taxonomy, but can also have implications for conservation.

Effect of predation risk on parasite transmission from first to second intermediate trematode hosts.

Predators can affect parasite-host interactions when directly preying on hosts or their parasites. However, predators may also have non-consumptive indirect effects on parasite-host interactions when hosts adjust their behaviour or physiology in response to predator presence. In this study, we examined how chemical cues from a predatory marine crab affect the transmission of a parasitic trematode from its first (periwinkle) to its second (mussel) intermediate host. Laboratory experiments revealed that chemical cues from crabs lead to a threefold increase in the release of trematode cercariae from periwinkles as a result of increased periwinkle activity. This positive effect on transmission was contrasted by a 10-fold reduction in cercarial infection rates in the second intermediate host when we experimentally exposed mussels to cercariae and predator cues. The low infection rates were caused by a substantial reduction in mussel filtration activity in the presence of predator cues, preventing cercariae from entering the mussels. To assess the combined net effect of both processes, we conducted a transmission experiment between infected periwinkles and uninfected mussels. Infection levels of mussels in the treatments with crab cues were sevenfold lower than in mussels without crab chemical cues. This suggests that predation risk effects on mussel susceptibility can counteract the elevated parasite release from first intermediate hosts, with negative net effects on parasite transmission. These experiments highlight that predation risk effects on parasite transmission can have opposing directions at different stages of the parasite's life cycle. Such complex non-consumptive predation risk effects on parasite transmission may constitute an important indirect mechanism affecting prevalence and distribution patterns of parasites in different hosts across their life cycle.

Usutu virus: a Flavivirus on the rise amid COVID-19 and monkeypox

Usutu virus: a Flavivirus on the rise amid COVID-19 and monkeypox

Emerging parasites and vectors in a rapidly changing world: from ecology to management

Global changes have influenced our societies in several ways with both positive (e.g., technology, transportation, and food security), and negative impacts (e.g., mental health problems, spread of diseases, and pandemics). Overall, these changes have affected the distribution patterns of parasites and arthropod vectors with the introduction and spreading of alien species in new geographical areas, eventually posing new challenges in public health. In this framework, the Acta Tropica Special Issue “Emerging parasites and vectors in a rapidly changing world: from ecology to management” provides a focus on the biology, ecology and management of emerging parasites and vectors of human and veterinary importance. Herein we review and discuss novel studies dealing with interactions of parasites and vectors with animals in changing environmental settings. In our opinion, a special focus on the implementation of management strategies of parasitic diseases to face anthropogenic environmental changes still represent a priority for public health. In the final section, key research challenges in this rapidly changing scenario are outlined.

Aggregation of Nematode, Hysterothylacium aduncum in whiting, Merlangius merlangus

Although aggregation of macroparasites characterized by unequal distribution of parasites on the host is a known axiom in marine fishes, aggregation of nematode, Hysterothylacium aduncum was not previously studied in whiting, Merlangius merlangus. Here, we investigated the host-related (fish condition factor) and parasite-related factors (parasite load) as well as the distribution pattern of H. aduncum in whiting to determine whether aggregation existed or not. The distribution of H. aduncum (third larval stage) in whiting has been shown to be aggregated. Aggregation of H. aduncum was assessed by Weibull distribution. The aggregation degree of nematode, H. aduncum in whiting was changed by the individual fish. The observed pattern of parasite distribution by the individual fish enabled the recognition of aggregation for the first time in whiting. The prediction of the intensity of H. aduncum in whiting improved the understanding of the host-parasite system, particularly for the dynamics of the parasite.

Distribution of host-specific parasites in hybrids of phylogenetically related fish: the effects of genotype frequency and maternal ancestry?

BackgroundHost specificity is one of the outputs of the coevolution between parasites and their associated hosts. Several scenarios have been proposed to explain the pattern of parasite distribution in parental and hybrid genotypes ranging from hybrid resistance to hybrid susceptibility. We hypothesized that host-parasite co-adaptation limits the infection of host-specific parasites in hybrid genotypes even under the condition of the high frequency of hybrids. The experimental monogenean infection in pure breeds of Blicca bjoerkna and Abramis brama and cross-breeds (the F1 generation of hybrids) under the condition of similar frequencies of pure and hybrid genotypes was investigated. We also examined the potential effect of the maternal origin of hybrids (potential co-adaptation at the level of mitochondrial genes) on monogenean abundance.MethodsPure breeds of two cyprinids and two cross-breeds (one with B. bjoerkna, the next with A. brama in the maternal positions) were exposed to infection by monogeneans naturally occurring in B. bjoerkna and A. brama. The experiment was run under similar frequencies of the four breed lines.ResultsWe showed similar levels of monogenean infection in B. bjoerkna and A. brama. However, each species harboured specific monogenean fauna. Hybrids harboured all monogenean species specifically infecting one or the other species. Monogenean infection levels, especially those of Dactylogyrus specific to A. brama, were lower in hybrids. For the majority of host-specific parasites, there was no effect of the maternal origin of hybrids on monogenean abundance. Asymmetry was found in the distribution of specific parasites in favour of specialists of B. bjoerkna in the monogenean communities of hybrids.ConclusionsOur results indicate that the maternal mtDNA of hybrids is not an important predictor of host-specific monogenean infection, which may suggest that mitochondrial genes are not strongly involved in the coadaptation between monogeneans and their associated hosts. The asymmetry of species-specific parasites suggests similarity between the molecular components of the immune mechanisms in hybrids and B. bjoerkna. Our results revealed a difference between the degree of host-parasite coadaptation in specific parasites of A. brama and the degree of host-parasite coadaptation in specific parasites of B. bjoerkna and their associated hosts.

How do seasonality and host traits influence the distribution patterns of parasites on juveniles and adults of Columba livia?

Parasites may influence host fitness and consequently exert a selective pressure on distinct phenotypes of the host population. This pressure can result in an evolutionary response, maintaining only individuals with certain traits in the population. The present study was aimed at identifying the morphological characteristics of juveniles and adults of Columba livia that may influence the distribution patterns of lice, Pseudolynchia canariensis and Haemoproteus columbae and how the populations of these parasites vary throughout the seasons of the year. Between July 2012 and July 2014, 377 specimens of C. livia were captured. We observed a significant increase in the mean intensities of infestation by pigeon flies and lice, as well as in species richness of ectoparasites during the warmest seasons, suggesting a reproductive synchrony between ectoparasites and host species. Bill length, body mass, and body length did not affect the infestation levels of ectoparasites on adults and juveniles of C. livia with three distinct plumage colors. In juveniles, plumage color affected only the mean intensity of infestation by lice, with Spread individuals as the most infested. This indicates that melanin in feathers was not an effective barrier against ectoparasites.

Patterns of parasite distribution in the hybrids of non-congeneric cyprinid fish species: is asymmetry in parasite infection the result of limited coadaptation?

Hybrids and their parasite diversity represent interesting models for evolutionary ecology. The modified immune response, shifted ecology, inheritance, and maternal ancestry of hybrid host fish are supposed to affect the diversity of their parasite communities. The pattern of metazoan parasite distribution in non-congeneric cyprinids – common bream (Abramis brama) and roach (Rutilus rutilus) (species with different morphology and ecology, and harbouring different specific parasites) – and their hybrids was analysed. Four static alternative scenarios based on parasite infection levels in hybrids and parental taxa are known. The hybrid resistance scenario predicts that hybrids are more resistant than parental taxa, resulting in low parasite infection in hybrids. This scenario is principally consistent with hybrid heterosis advantage. In accordance with this prediction, metazoan parasite abundance and prevalence were higher in parental species when compared with their hybrids. Alternatively, the dynamic Red Queen scenario of infection in hybridising systems predicts parasite adaptation to common hosts. Temporal (six sampling events) and spatial (two sampling sites) aspects as possible factors influencing parasite distribution were analysed. We found no support for this hypothesis, i.e. no changes in the frequency of hybrids or their parental species and no changes in parasite infection in parental species or hybrids were found in the different time periods. The effect of maternal ancestry on infection level was evident; hybrids exhibiting common bream mtDNA were more strongly parasitized by digeneans and crustaceans than hybrids exhibiting roach mtDNA. Hybrids harboured a majority of the specific parasites of both parental species; however, the level of infection of common bream-specific parasites (especially monogeneans) in hybrids was low. Such an asymmetrical distribution of parental species-specific parasites in hybrids may suggest the limited inheritance of protective immunological mechanisms from one parental species and reveal stronger coadaptation between common bream and its specific parasites.

Sex differences in flea infections among rodent hosts: is there a male bias?

Recognizing patterns of parasite distribution among wildlife hosts is of major importance due to growing risk of transmission of zoonotic diseases to humans. Thus, sex-dependent parasite distribution in higher vertebrates is extensively studied, and males are often found more parasitized than females. Male-biased parasitism may be the result of weaker immunocompetence of male hosts owing to the immunosuppressive effect of androgens. Moreover, larger hosts (males) may demonstrate higher parasite infestation levels than smaller individuals (females), as they constitute a better nutritional resource for parasites and provide them with a greater variety of niches. In the present work, we investigated sex-dependent patterns of flea distribution among three common rodent species (Apodemus agrarius, Apodemus flavicollis, and Myodes glareolus). We hypothesized that males have a higher flea infestation than females. We confirm male-biased parasitism in A. agrarius and M. glareolus, but not in A. flavicollis. Additionally, flea infestation increased with body mass in A. agrarius, but not in A. flavicollis and M. glareolus. The detected differences in parasite distribution among sexes are probably the result of immunosuppressive effects of androgens and spatial behavior of males.

Parasite co-infection and interaction as drivers of host heterogeneity

We examined the hypothesis that the interaction between concomitant infecting parasites modifies host susceptibility, parasite intensity and the pattern of parasite distribution within the host population. We used a 26 year time series of three common parasites in a natural population of rabbits: two gastrointestinal nematodes (Trichostrongylus retortaeformis and Graphidium strigosum) and the immunosuppressive myxoma virus. The frequency distribution of nematodes in the host population and the relationship between host age and nematode intensity were explored in rabbits with either single or dual nematode infections and rabbits infected with the nematodes and myxoma virus. The aggregation of T. retortaeformis and G. strigosum among the rabbits varied with the nature of the co-infection both in male and female hosts. The two nematodes exhibited different age–intensity profiles: G. strigosum intensity increased exponentially with host age while T. retortaeformis intensity exhibited a convex shape. The presence of a secondary infection did not change the age–intensity profile for G. strigosum but for T. retortaeformis co-infection (either both nematodes or myxoma-nematodes) resulted in significantly greater intensities in adult hosts. Results suggest that multi-species infections contributed to aggregation of parasites in the host population and to seasonal variation in intensity, but also enhanced differences in parasitism between sexes. This effect was apparent for T. retortaeformis, which appears to elicit a strong acquired immune response but not for G. strigosum which does not produce any evident immune reaction. We concluded that concomitant infections mediated by host immunity are important in modifying host susceptibility and influencing heterogeneity amongst individual hosts.

Ultimate mechanisms of age-biased flea parasitism

Mechanisms that cause nonrandom patterns of parasite distribution among host individuals may influence the population and evolutionary dynamics of both parasites and hosts, but are still poorly understood. We studied whether survival, reproduction, and behavioral responses of fleas (Xenopsylla conformis) changed with the age of their rodent hosts (Meriones crassus), experimentally disentangling two possible mechanisms: (a) differential survival and/or fitness reward of parasites due to host age, and (b) active parasite choice of a host of a particular age. To explore the first mechanism, we raised fleas on rodents of two age groups and assessed flea survival as well as the quantity and quality of their offspring. To explore the second mechanism, three groups of fleas that differed in their previous feeding experience (no experience, experience on juvenile or experience on adult rodents) were given an opportunity to choose between juvenile and adult rodents in a Y-maze. Fleas raised on juvenile rodents had higher survival and had more offspring that emerged earlier than fleas raised on adults. However, fleas did not show any innate preference for juvenile rodents, nor were they able to learn to choose them. In contrast to our predictions, based on a single previous exposure, fleas learned to choose adult rodents. The results suggest that two mechanisms-differential survival and fitness reward of fleas, and associative learning by them-affect patterns of flea distribution between juvenile and adult rodents. The former increases whereas the latter reduces flea densities on juvenile rodents. The ability of fleas to learn to choose adult but not juvenile hosts may be due to: (a) a stronger stimulus from adults, (b) a higher profitability of adults in terms of predictability and abundance, or (c) the evolutionary importance of recognizing adult but not juvenile hosts as representatives of the species.

Parasites as biological tags for stock discrimination in marine fish from South American Atlantic waters

The use of parasites as biological tags in population studies of marine fish in the south-western Atlantic has proved to be a successful tool for discriminating stocks for all species to which it has been applied, namely: Scomber japonicus, Engraulis anchoita, Merluccius hubbsi and Cynoscion guatucupa, the latter studied on a broader geographic scale, including samples from Uruguayan and Brazilian waters. The distribution patterns of marine parasites are determined mainly by temperature-salinity profiles and by their association with specific masses of water. Analyses of distribution patterns of some parasite species in relation to gradients in environmental (oceanographic) conditions showed that latitudinal gradients in parasite distribution are common in the study area, and are probably directly related to water temperature. Indeed, temperature, which is a good predictor of latitudinal gradients of richness and diversity of species, shows a latitudinal pattern in south-western Atlantic coasts, decreasing southwards, due to the influence of subtropical and subantarctic marine currents flowing along the edge of the continental slope. This pattern also determines the distribution of zooplankton, with a characteristic specific composition in different water masses. The gradient in the distribution of parasites determines differential compositions of their communities at different latitudes, which makes possible the identification of different stocks of their fish hosts. Other features of the host-parasite systems contributing to the success of the parasitological method are: (1) parasites identified as good biological tags (i.e. anisakids) are widely distributed in the local fauna; (2) many of these species show low specificity and use paratenic hosts; and (3) the structure of parasite communities are, to a certain degree, predictable in time and space.

BIONOMICS OF LARVAE OF PARELAPHOSTRONGYLUS ODOCOILEI (NEMATODA: PROTOSTRONGYLIDAE) IN EXPERIMENTALLY INFECTED GASTROPOD INTERMEDIATE HOSTS

Parelaphostrongylus odocoilei is a protostrongylid parasite that has recently been recognized at several locations in sub-Arctic, but not Arctic, North America. We investigated factors that may determine the distribution of P. odocoilei, including suitable gastropod intermediate hosts, temperature requirements for larval development in gastropods, and larval emergence facilitating overwinter transmission. We collected and experimentally infected gastropods from a site in the sub-Arctic where P. odocoilei is at the northern limit of its distribution. Deroceras laeve, Catinella sp., and Euconulus cf fulvus, but not members of the Pupillidae, were suitable intermediate hosts. We describe bionomics of larvae of P. odocoilei in D. laeve and Catinella sp. Infective larvae emerged from all slugs (D. laeve) and 60% of Catinella sp. snails, and emergence from D. laeve was intensity dependent. Emerged infective larvae survived up to 6 mo under conditions approximating that of the subnivean environment. In D. laeve, there was a direct relationship between temperature and development rate of larvae of P. odocoilei. Larvae of P. odocoilei did not develop to infective stage below the theoretical threshold (8.5 C), and required a minimum of 163 degree days to complete development. These developmental parameters can be incorporated into a model to predict larval development in the field. Knowledge of the factors influencing larval bionomics provides the foundation for predicting temporal and spatial patterns of parasite distribution, abundance, and transmission.

Frequency distribution of parasites in host populations: review

A review on investigations of parasite frequency distribution in host population is presented. An application of theoretical distribution models for approximation of empirical data, the causes predetermining pattern of parasite distribution, the connection among distribution parameters, as well as the connection between distribution patterns and mechanisms of population regulation are analysed.

The Spatial Demography of Mistletoe Parasitism on a Yemeni Acacia

The frequency of parasitism of a mistletoe, Plicosephalus curviflorus, on Acacia tortilis as a function of host density and host size was investigated. The influence of host size and parasite frequency on flowering success of the parasite was also investigated. Parasitism was contagiously distributed but occurred most intensely in low-density Acacia stands. The distribution of Acacia size classes showed spatial autocorrelation, with smaller, more shrublike trees occurring in high-density clusters. Parasitism frequency and intensity were highest on larger trees, indicating that the spatial patterns of parasite distribution could be explained in part by the spatial patterns of the host size classes. Flowering success of mistletoes was not influenced by tree size but was negatively correlated with the number of mistletoes on the host. The late onset of parasitic attack with respect to the age or size of the host and the negative conspecific density effects on flowering success by the parasite could reduce adverse fitness effects on the host and thereby increase the probability of stable coexistence of A. tortilis and P curviflorus. The size structure of the host population, by influencing the distribution of parasites among the hosts, may influence the population dynamics of the parasite and the stability of the host-parasite association.

Revision of Haliotrema species (Monogenea: Ancyrocephalidae) from Atlantic boxfishes (Tetraodontiformes: Ostraciinae): morphology, morphometrics, and distribution

Six species of Haliotrema, H. lactophrys, H. guadeloupensis, H. glandulosum, H. torridum, H. minutum, and H. kritskyi, found on the gills of seven species of Atlantic boxfishes (Ostraciinae) of the genera Acanthostracion and Lactophrys are redescribed. These species are found to be more similar to Haliotrema species on perciform hosts (i.e., Chaetodontidae, Labridae, and Mullidae) from the Caribbean than to congeners on other tetraodontiform hosts. In addition to clear morphological distinction, the results of a canonical discriminant analysis on 30 morphometric variables indicated that these variables also contribute, as a correlated group, to species distinction (p = 0.0001). The synergistic relation among the variables was identified as a shape component associated most strongly with the dorsal and ventral hamuli. The distributions of these parasite species indicated that none is specific to any one host species; specificity was more pronounced at the host genus level. Patterns of parasite distribution on host populations indicated a complicated distribution history.

Population dynamics of helminth parasites in wild and laboratory rodents

AbstractThis paper reviews the host‐helminth interactions that are of importance in regulating both the abundance of helminth parasites of rodents and the host population abundance. Parasite density has an effect on the ability of individual parasites to grow, reproduce and survive within the definitive host, and it also influences the ability of the infected host to survive and reproduce. The severity of the impact of such density‐dependent responses is related to the pattern of parasite distribution within the host population. The potential of helminth parasites to regulate the abundance of a small mammal population is illustrated using an experimental example. Areas identified for further research include (i) an investigation of the relative importance of parasite density‐dependent effects on parasite and host survival and reproduction for specific host‐helminth associations; (ii) more research into the impact of helminth density on host reproduction; and (iii) research into the impact of helminths on the population dynamics of small mammal populations using field and laboratory experiments designed to assess the relative importance of helminths in regulating the abundance of their host populations.SummaryIn this paper we have considered parasite density as an important determinant of parasite and host population dynamics. Because the relative impact of density on different population processes will differ for different helminths, researchers interested in accounting for temporal dynamics of a specific parasite will need to investigate the density‐dependent processes involved in the life cycle of that helminth.Although interactions between the population biology of both the host and helminth parasite are of fundamental importance to the population dynamics of the parasite, they also are important in determining the population dynamics of the infected host population. Because helminths, by definition, must have an impact on the ability of the host population to survive or reproduce they, therefore, also have the potential to regulate the abundance of the host population (Anderson & May, 1978; Anderson, 1979). More research is needed on the effect of parasite density on the rate of reproduction of infected hosts. Finally, given recent theoretical and experimental evidence that parasites can regulate mammal populations, much work is needed to determine conditions when this actually occurs in the field.

Distribution of two species of Kudoa (Myxozoa: Multivalvulida) in the offshore population of the Pacific hake, Merluccius productus (Ayres, 1855)

Samples of pacific hake (Merluccius productus), a total of 581 fish, were collected along its distribution range from California to Vancouver Island. The fish were examined for prevalence and intensity of infection with Kudoa thyrsitis and K. paniformis (Myxozoa). Fish age 4+ (and older) were more heavily infected than those age 3+, the most heavily infected part of the fish being the dorsal musculature directly behind the head. Although the prevalence of infection with K. thyrsitis increased in a northerly direction, its intensity was markedly lower than the intensity of infection with K. paniformis. Fish of comparable age and size were twice as heavily infected with K. paniformis off California as those taken off Vancouver Island. Fish infected with K. thyrsitis appeared to show a much stronger reaction to the presence of the parasite by producing relatively more black pseudocysts than those infected with K. paniformis. Reasons for this fact and for the observed pattern of parasite distribution are discussed.

Impact of Ecological Succession on the Parasite Fauna in Centrarchids from Oligotrophic and Eutrophic Ecosystems

Approximately 30 species of larval and adult parasites were collected from 549 centrarchid fish and 7718 gastropod molluscs from an oligotrophic and two eutrophic lakes in southwestern Michigan. The distribution pattern indicates that centrarchids from the oligotrophic lake harbor a wide range of species of adult parasites and a comparatively smaller number of larval forms, many of which complete their life cycles in predatory fish. On the other hand, bass and sunfish from the two eutrophic lakes harbor a proportionately larger number of larval parasites, most of which culminate their life cycles in fish-eating birds and mammals. A trophic hypothesis, based on the nature of predatorprey relationships in each of the two types of ecosystem, is proposed to explain the distribution patterns of parasites.