The helminth parasites of the wild rabbit Oryctolagus cuniculus and their effect on host condition in Dunas de Mira, Portugal

The energetic costs of sub-lethal helminth parasites in mammals: a meta-analysis

Parasites, by definition, have a negative effect on their host. However, in wild mammal health and conservation research, sub-lethal infections are commonly assumed to have negligible health effects unless parasites are present in overwhelming numbers. Here, we propose a definition for host health in mammals that includes sub-lethal effects of parasites on the host's capacity to adapt to the environment and maintain homeostasis. We synthesized the growing number of studies on helminth parasites in mammals to assess evidence for the relative magnitude of sub-lethal effects of infection across mammal taxa based on this expanded definition. Specifically, we develop and apply a framework for organizing disparate metrics of parasite effects on host health and body condition according to their impact on an animal's energetic condition, defined as the energetic burden of pathogens on host physiological and behavioural functions that relate directly to fitness. Applying this framework within a global meta-analysis of helminth parasites in wild, laboratory and domestic mammal hosts produced 142 peer-reviewed studies documenting 599 infection-condition effects. Analysing these data within a multiple working hypotheses framework allowed us to evaluate the relative weighted contribution of methodological (study design, sampling protocol, parasite quantification methods) and biological (phylogenetic relationships and host/parasite life history) moderators to variation in the magnitude of health effects. We found consistently strong negative effects of infection on host energetic condition across taxonomic groups, with unusually low heterogeneity in effect sizes when compared with other ecological meta-analyses. Observed effect size was significantly lower within cross-sectional studies (i.e. observational studies that investigated a sub-set of a population at a single point in time), the most prevalent methodology. Furthermore, opportunistic sampling led to a weaker negative effect compared to proactive sampling. In the model of host taxonomic group, the effect of infection on energetic condition in carnivores was not significant. However, when sampling method was included, it explained substantial inter-study variance; proactive sampling showing a strongly significant negative effect while opportunistic sampling detected only a weak, non-significant effect. This may partly underlie previous assumptions that sub-lethal parasites do not have significant effects on host health. We recommend future studies adopt energetic condition as the framework for assessing parasite effects on wildlife health and provide guidelines for the selection of research protocols, health proxies, and relating infection to fitness.

Specifics of the morphological identification of the pathogen of passaluariasis of rabbits

Passalurus ambiguus (Nematoda, Oxyuroidae) is one of the most common parasites of digestive tract of domestic and wild rabbits and rodents. Passalurus spp. are cosmopolitan, and the mature nematodes are localized in the appendages and large intestine of animals. The passaluariasis infections remain quite relevant in modern rabbit breeding, because the disease is highly contagious, with the possibility of unlimited spread inducing significant economic losses. The aim of the study was to determine the identifying morphological species characteristics of P. ambiguus nematodes, which were isolated from the colon of domestic rabbits (Oryctolagus cuniculus domesticus). The identifying characters of Passalurus include morphological features, namely the presence of a spherical bulb in the esophagus, and the presence of three teeth in the oral capsule. Males of P. ambiguus have a characteristic structure of the tail end, namely the presence of papillary protrusions and a massive narrowed part with a spicule handle, and five papillae around the cloaca. Twenty-eight metric indicators are proposed that characterize the size of the body, oral capsule, esophagus in different parts of it, the tail end, spicules, the location of the cloaca. Two different morphotypes of mature females of P. ambiguus were revealed – short-tailed and long-tailed, which were larger by 19 indicators (by 3.2–43.6%). The morphotypes of P. ambiguus females are characterized; the length of the tail, body length and width in different areas, depth of the oral capsule, esophageal size and its structural elements, the location of the vulva and nerve ring, the width of the caudal process. At the same time, the parameters of esophageal bulb length and caudal process in short-tailed females were higher (by 13.9% and 11.9%, respectively) than in the long-tailed females. A total of 25 morphometric parameters were proposed for the identification of P. ambiguus females. The obtained data indicate the feasibility of further research on the causes of occurrence of such morphotypes in P. ambiguus females and the need to take into account the existence of such forms of females for their differential diagnosis taking into account their proposed morphometric parameters.

Exotic Species and Autochthonous Parasites: Trichostrongylus Retortaeformis in Eastern Cottontail

Introduction: A parasite community is usually well adapted and specific to the host species they co-evolved with. Although exotic pathogens infecting autochthonous species have been documented, the infection of an alien species with native parasites is rare in lagomorphs. Trichostrongylus retortaeformis is a nematode parasite infecting the small intestine of domestic and wild lagomorphs in Europe. Methods: Thirty-two Eastern cottontails from a naturalized population in Italy were processed to describe the gastrointestinal parasite community. Results and discussions: T. retortaeformis is reported for the first time in the Eastern cottontail Sylvilagus floridanus introduced to Europe. The Eastern cottontail is an invasive lagomorph, living in sympatry with the autochthonous European brown hare in certain areas of Italy. This study provides new insights into the dynamics of parasite communities of native and alien lagomorph species in sympatric areas.

Pathomorphological changes in the large intestine of rabbits parasitised by Passalurus ambiguus (Nematoda, Oxyuridae)

Passaluriasis is a common infestation of lagomorphs, which clinically manifests in intense itching around the anus, various disorders of digestion and loss of weight. We performed a study of infested rabbits of the seryi veleten breed, which were kept in individual farms in Poltava Oblast (Ukraine). During the autopsy, in the cavity of the large intestine, there were found small, spindle-like helminths of white colour. Out of 10 rabbits, 846 nematodes were extracted (369 males and 477 females, identified as Passalurus ambiguus (Rudolphi, 1819) Dujardin, 1845. It was determined that the extensity of infestation in female rabbits reached 56.4%, male rabbits – 43.6%. The results of metric parameters of the nematodes are as follows: mean body length of males equaled 4.6 ± 0.4, females – 9.7 ± 1.21 mm, and maximum width – 257.4 ± 17.8 and 546.2 ± 37.1 µm respectively. A common feature of mature nematodes of this species is the presence of a rounded extension (bulbus) at the end of the esophagus. During chronic course of passaluriasis in rabbits, pathomorphological changes developed in the large intestine. The upper epithelium of the large intestine was damaged in some places, certain epithelian cells were found in the lumen of the intestine. The intestinal glands are widened, filled with slimy content of mostly dark blue-violet colour, especially in the upper sections of the glands. In the deep sections of the glands, slime was almost transparent. In deep sections of the glands the slime was almost transparent. In the epithelium cells of the glands, slimy granules were also of basophilic colour. The muscularis mucosae of the mucous membrane, especially between the intestinal glands was swollen, had practically no colour, the collagen fibers were stretched, thinned-out. Edemas were also recorded in the tela submucosa. In some preparations, the muscularis mucosae was notably infiltrated by lymphoid cells and histiocytes. On large extensions, we found some signs of hypersecretion of slime in goblet cells of the intestinal glands as accumulations of granules of slime in the cytoplasm, which had poorly developed colouration. On the side of the muscular and serous membranes, no pathological changes were found. The information presented here indicates the relevance of passaluriasis infestation as an etiological factor of occurrence of chronic catarrhal colitis with lymphohistiocytosis.

Immuno-epidemiology of chronic bacterial and helminth co-infections: observations from the field and evidence from the laboratory

Co-infections can alter the host immune responses and modify the intensity and dynamics of concurrent parasitic species. The extent of this effect depends on the properties of the system and the mechanisms of host-parasite and parasite-parasite interactions. We examined the immuno-epidemiology of a chronic co-infection to reveal the immune mediated relationships between two parasites colonising independent organs, and the within-host molecular processes influencing the dynamics of infection at the host population level. The respiratory bacterium, Bordetella bronchiseptica, and the gastrointestinal helminth, Graphidium strigosum, were studied in the European rabbit (Oryctolagus cuniculus), using long-term field data and a laboratory experiment. We found that 65% of the rabbit population was co-infected with the two parasites; prevalence and intensity of co-infection increased with rabbit age and exhibited a strong seasonal pattern with the lowest values recorded during host breeding (from April to July) and the highest in the winter months. Laboratory infections showed no significant immune-mediated effects of the helminth on bacterial intensity in the lower respiratory tract but a higher abundance was observed in the nasal cavity during the chronic phase of the infection, compared with single bacterial infections. In contrast, B. bronchiseptica enhanced helminth intensity and this was consistent throughout the 4-month trial. These patterns were associated with changes in the immune profiles between singly and co-infected individuals for both parasites. This study confirmed the general observation that co-infections alter the host immune responses but also highlighted the often ignored role of bacterial infection in helminth dynamics. Additionally, we showed that G. strigosum had contrasting effects on B. bronchiseptica colonising different parts of the respiratory tract. At the host population level our findings suggest that B. bronchiseptica facilitates G. strigosum infection, and re-infection with G. strigosum assists in maintaining bacterial infection in the upper respiratory tract and thus long-term persistence.

Soboliphyme baturini infection does not affect the nutritional condition of American marten (Martes americana) in Alaska

Soboliphyme baturini, a stomach-dwelling nematode of American martens (Martes Americana), reaches high levels of infection; however, its effects on the nutritional condition of the host are unknown. To understand the effects of this parasite on American martens, we collected S. baturini and measured abdominal fat deposits from 155 marten carcasses on Prince of Wales Island, southeastern Alaska, in the winter 2006-2007. We analyzed how the dried mass of abdominal fat varied as a function of S. baturini intensity. Parasite intensity and nutritional condition were not correlated; these results suggest that American martens were able to withstand even very high levels of S. baturini infection (up to 178 parasites per host).