Model parasite species, whose entire life cycle can be completed in the laboratory and maintained for multiple generations, have played a fundamental role in our understanding of host–parasite interactions. Yet, keeping parasites in laboratory conditions may expose them to unnatural evolutionary pressures, and using laboratory cultures for research is therefore not without limitations. Using 2 widely-used model helminth species, the cestode Hymenolepis diminuta and the nematode Heligmosomoides polygyrus, I illustrate the caution needed when interpreting experimental results on model species. I first review more than 1200 experimental studies published on these species in the past 4 decades, to determine which research areas they have contributed to. This is followed by an examination of the institutional laboratory cultures that have provided the parasites used in these studies. Some of these have persisted for decades and accounted for a substantial proportion of published studies, whereas others have been short-lived. Using information provided by the curators of active cultures, I summarize data on their origins and maintenance conditions. Finally, I discuss how laboratory cultures may have been subject to the influence of evolutionary genetic processes, such as founder effects, genetic drift and inbreeding. I also address the possibility that serial passage through laboratory hosts across multiple generations has exerted artificial selection on several parasite traits, resulting in genetic and phenotypic divergence among laboratory cultures, and between these cultures and natural parasite populations. I conclude with recommendations for the continued usage of laboratory helminth cultures aimed at maximizing their important contribution to parasitological research.

The factors that influence parasite associated bacterial microbial diversity and the geographic distributions of bacteria are not fully understood. In an effort to gain a deeper understanding of the relationship between the bacterial diversity of Ctenocephalides fleas and host species and the external environment, we conducted a metagenetic analysis of 107 flea samples collected from 8 distinct sampling sites in South Africa. Pooled DNA samples mostly comprising of 2 or 3 individuals sampled from the same host, and belonging to the same genetic cluster, were sequenced using the Ion PGM™ Hi-Q™ Kit and the Ion 316™ Chip v2. Differences were detected in the microbiome compositions between Ctenocephalides felis, Ctenocephalides canis and Ctenocephalides connatus. Although based on a small sample, C. connatus occurring on wildlife harboured a higher bacterial richness when compared to C. felis on domestic animals. Intraspecific differences in the microbial OTU diversity were detected within C. f. felis that occurred on domestic cats and dogs. Different genetic lineages of C. f. felis were similar in microbial compositions but some differences exist in the presence or absence of rare bacteria. Rickettsia and Bartonella OTU's identified in South African cat fleas differ from those identified in the USA and Australia. Intraspecific microbial compositions also differ across geographic sampling sites. Generalized dissimilarity modelling showed that temperature and humidity are potentially important environmental factors explaining the pattern obtained.

Atlantic salmon (Salmo salar) is repeatedly exposed to and infected with ectoparasitic salmon lice (Lepeophtheirus salmonis) both in farms and in nature. However, this is not reflected in laboratory experiments where fish typically are infected only once. To investigate if a previous lice infection affects host response to subsequent infections, fish received 4 different experimental treatments; including 2 groups of fish that had previously been infected either with adult or infective salmon lice larvae (copepodids). Thereafter, fish in all treatment groups were infected with either a double or a single dose of copepodids originating from the same cohort. Fish were sampled when lice had developed into the chalimus, the pre-adult and the adult stage, respectively. Both the specific growth rate and cortisol levels (i.e. a proxy for stress) of the fish differed between treatments. Lice success (i.e. ability to infect and survive on the host) was higher in naïve than in previously infected fish (pre-adult stage). The expression of immune and wound healing transcripts in the skin also differed between treatments, and most noticeable was a higher upregulation early in the infection in the group previously infected with copepodids. However, later in the infection, the least upregulation was observed in this group, suggesting that previous exposure to salmon lice affects the response of Atlantic salmon towards subsequent lice infections.

Individual hosts are often co-infected with multiple parasite species. Evidence from theoretical and empirical studies supports the idea that co-occurring parasites can impact each other and their hosts via synergistic or antagonistic interactions. The fundamental aim of understanding the consequences of co-infection to hosts and parasites requires an understanding of patterns of species co-occurrence within samples of hosts. We censused parasite assemblages in 755 adult, male fathead minnows collected from 7 lakes/ponds in southern Alberta, Canada between 2018 and 2020. Fifteen species of endoparasites infected fathead minnows, 98% of which were co-infected with between 2 and 9 parasite species (mean species richness: 4.4 ± 1.4). Non-random pairwise associations were detected within the overall parasite community. There were particularly strong, positive associations in the occurrences and intensities of the 2 congeneric larval trematodes Ornithodiplostomum sp. and Ornithodiplostomum ptychocheilus that comprised >96% of the 100 000+ parasites counted in the total sample of minnows. Furthermore, the occurrence of Ornithodiplostomum sp. was a strong predictor of the occurrence of O. ptychocheilus, and vice versa. Positive covariation in the intensities of these 2 dominants likely arises from their shared use of physid snails as first intermediate hosts in these waterbodies. These 2 species represent a predictable and non-random component within the complex assemblage of parasites of fathead minnows in this region.

In recent field studies, suspected gymnophallid metacercariae were histologically located in the mantle of mussels from the Norwegian Sea. Mussels from the sites in which that infection was detected also presented abnormally high pearl numbers. It has been previously described that gymnophallid metacercariae could cause pearl formation processes in mussels, as a host reaction to encapsulate these metacercariae. Given the pathological host reaction these parasites elicit, a study was performed to identify gymnophallid metacercariae found in mussels collected from Tromsø at morphological and molecular level and to assess, by the use of molecular tools, the relationship between the parasite and the biological material inside the pearls. As a result, Gymnophallus bursicola metacercariae infecting Norwegian Mytilus edulis were identified according to morphological characters, along with the first 18S rDNA and COI sequences for this trematode species. In addition, parasite DNA from the core of the pearls was extracted and amplified for the first time, confirming the parasitological origin of these pearls. This procedure could allow identifying different parasitic organisms responsible for the generation of pearls in bivalves.

Nematode spicules play a vital role in the reproductive activity of species that possess them. Our primary objective was to compare the lengths of spicules of the laboratory mouse (Mus musculus) – maintained isolate H. bakeri – with those of H. polygyrus from naturally infected wood mice (Apodemus sylvaticus). On a more limited scale, we also included H. glareoli from bank voles (Myodes glareolus), a species reputed to possess longer spicules than either of the 2 former species. In total, we measured 1264 spicules (H. bakeri, n = 614; H. polygyrus n = 582; and H. glareoli, n = 68). There was a highly significant difference between the spicule lengths of the Nottingham-maintained H. bakeri (mean = 0.518 mm) and H. polygyrus (0.598 mm) from 11 different localities across the British Isles. A comparison of the spicules of H. bakeri maintained in 4 different laboratories in 3 continents revealed a range in the mean values from 0.518 to 0.540 mm, while those of worms from Australian wild house mice were shorter (0.480 mm). Mean values for H. polygyrus from wood mice from the British Isles ranged from 0.564 to 0.635 mm, although isolates of this species from Norway had longer spicules (0.670 mm). In agreement with the literature, the spicules of H. glareoli were considerably longer (1.098 mm). Since spicules play a vital role in the reproduction of nematode species that possess them, the difference in spicule lengths between H. bakeri and H. polygyrus adds to the growing evidence that these 2 are quite distinct species and likely reproductively isolated.

Combining the biogeography and phylogenetic patterns of parasite-host associations allows a better understanding of the history of parasite–host interactions, which can be achieved via biogeographic regionalization incorporating phylogenetic information. Recently, the concepts of evoregions (regions where a majority of species evolved from one or several ancestors inhabiting these regions) and evolutionary transition zones (regions of high phylogenetic turnover) have been proposed, coupled with a classification approach for these concepts. We applied this approach to 206 flea species and 265 host species of the Palearctic and aimed to identify evoregions and evolutionary transition zones for both fleas and hosts and to understand whether these evoregions and transition zones match each other. We identified 5 evoregions with 3 transition zones for either fleas or hosts, but neither the positions and boundaries of the flea and host evoregions nor the transition zones coincided. Indications of multiple geographic centres of diversification of the same flea lineages suggested that (a) the common evolutionary history of fleas and hosts was characterized by multiple events other than codiversification and that (b) dispersal played an important role in flea and host assemblies. Barriers to dispersal could be represented by landscape features (deserts and mountain ranges) and/or climate differences.

The distribution of parasites is shaped by a variety of factors, among which are the migratory movements of their hosts. Israel has a unique position to migratory routes of several bird species leaving Europe to winter in Africa, however, detailed studies on the parasite fauna of birds from this area are scarce. Our study investigates occurrence and distribution of sibling species among Contracaecum rudolphii complex in Phalacrocorax carbo sinensis from Italy and Israel, to acquire further information on the geographical range of these species to gain deeper knowledge on the ecology of these parasites and their bird host. A total of 2383 Contracaecum were collected from the gastric mucosa of 28 great cormorants (18 from Israel and 10 from Italy). A subsample was processed for morphological analyses in light and scanning electron microscopy (SEM), and for molecular analyses through amplification and sequencing of the ITS rDNA and the cox2 mtDNA, and through PCR-RFLP. All the 683 Contracaecum subjected to molecular identification belonged to C. rudolphii s.l., (300 C. rudolphii A and 383 C. rudolphii B). SEM micrographs provided, for the first time, details of taxonomic structures in male specimens from both sibling species, and the first SEM characterization of C. rudolphii B. This work presents the first data on the occurrence of sibling species of C. rudolphii in Israel and provides additional information on the distribution of C. rudolphii A and B in Italy, confirming the high prevalence and intensity of infection observed in Ph. carbo sinensis from other Italian areas.

Effective supply chain management is a critical pillar of well-functioning health systems ensuring that medical commodities reach those in need. In Liberia, the national neglected tropical disease (NTD) programme supports health systems strengthening for case management of NTDs. Integration of NTD commodities into the national health system supply chain is central to the integrated approach; however, there is minimal evidence on enablers and barriers. Drawing on qualitative evaluation data, we illustrate that perceived benefits and strengths to integrating NTD commodities into the supply chain include leveraged storage and management capacities capitalized at lower system levels; the political will to integrate based on cost-saving and capacity strengthening potential and positive progress integrating paper-based reporting tools. Challenges remain, specifically the risk of reliance on donor funding; difficulty in accessing commodities due to bureaucratic bottlenecks; lack of inclusion of NTD commodities within electronic data tools and poor coordination leading to an inability to meet demand. Collectively, the negative consequences of ineffective integration of NTD commodities into the supply chain has a detrimental impact on health workers (including community health workers) unable to deliver the quality of care to patients. Trust between affected populations and the health system is compromised when treatments are unavailable.

Piroplasms, which include the agents of cattle fever and human and dog babesiosis, are a diverse group of blood parasites of significant veterinary and medical importance. The invasive Asian longhorned tick, Haemaphysalis longicornis, is a known vector of piroplasms in its native range in East Asia and invasive range in Australasia. In the USA, H. longicornis has been associated with Theileria orientalis Ikeda outbreaks that caused cattle mortality. To survey invasive populations of H. longicornis for a broad range of piroplasms, 667 questing H. longicornis collected in 2021 from 3 sites in New Jersey, USA, were tested with generalist piroplasm primers targeting the 18S small subunit rRNA (395–515 bp, depending on species) and the cytochrome b oxidase loci (1009 bp). Sequences matching Theileria cervi type F (1 adult, 5 nymphs), an unidentified Theileria species (in 1 nymph), an undescribed Babesia sensu stricto (‘true’ Babesia, 2 adults, 2 nymphs), a Babesia sp. Coco (also a ‘true Babesia’, 1 adult, 1 nymph), as well as Babesia microti S837 (1 adult, 4 nymphs) were recovered. Babesia microti S837 is closely related to the human pathogen B. microti US-type. Additionally, a 132 bp sequence matching the cytochrome b locus of deer, Odocoileus virginanus, was obtained from 2 partially engorged H. longicornis. The diverse assemblage of piroplasms now associated with H. longicornis in the USA spans 3 clades in the piroplasm phylogeny and raises concerns of transmission amplification of veterinary pathogens as well as spillover of pathogens from wildlife to humans.

Optical microscopy is the gold standard technique used to confirm the diagnosis of scabies. Multiple diagnostic features of the pathogen Sarcoptes scabiei var. hominis (S. scabiei) can be identified under a microscope and classified into 3 categories: mites, eggs and fecal pellets. However, mite and eggshell fragments can also be observed, which have been ignored in the 2020 International Alliance for the Control of Scabies (IACS) Criteria and by most researchers. In this study, we propose a novel morphological classification method that classifies multiple diagnostic features into 5 categories and 7 subcategories. Our results revealed that 65.2% (1893 of 2896) of the positive cases were confirmed through the identification of mites, eggs or fecal pellets, whereas up to 34.6% (1003 of 2896) of the positive cases were confirmed through the identification of mite or eggshell fragments. Therefore, the important diagnostic values of mite and eggshell fragments should be emphasized. Importantly, for the first time, mite and eggshell fragments were classified into 7 subcategories, some of which are easily ignored or confused with contaminating artefacts. We believe that this novel morphological classification method will be beneficial for operator training in interpreting slides and in improving the 2020 IACS Criteria.