Parasite life-cycle studies: a plea to resurrect an old parasitological tradition

Abstract

Many helminth taxa have complex life cycles, involving different life stages infecting different host species in a particular order to complete a single generation. Although the broad outlines of these cycles are known for any higher taxon, the details (morphology and biology of juvenile stages, specific identity of intermediate hosts) are generally unknown for particular species. In this review, we first provide quantitative evidence that although new helminth species are described annually at an increasing rate, the parallel effort to elucidate life cycles has become disproportionately smaller over time. We then review the use of morphological matching, experimental infections and genetic matching as approaches to elucidate helminth life cycles. Next we discuss the various research areas or disciplines that could benefit from a solid knowledge of particular life cycles, including integrative taxonomy, the study of parasite evolution, food-web ecology, and the management and control of parasitic diseases. Finally, we end by proposing changes to the requirements for new species descriptions and further large-scale attempts to genetically match adult and juvenile helminth stages in regional faunas, as part of a plea to parasitologists to bring parasite lifecycle studies back into mainstream research.

A molecular phylogenetic appraisal of the acanthostominesAcanthostomumandTimoniellaand their position within Cryptogonimidae (Trematoda: Opisthorchioidea)

“…Studies of cryptogonimids (and trematodes in general) are negatively impacted by the lack of taxonomical records of helminth parasites of freshwater and marine fishes of different regions ( Scholz & Choudhury, 2014 ; Cribb et al, 2016 ; Vidal-Martínez, Torres-Irineo & Aguirre-Macedo, 2016 ), as well as the lack of knowledge concerning intermediate and definitive host life cycles ( Cribb & Bray, 2011 ; Blasco-Acosta & Poulin, 2017 ). This has led to a reduction in postulated evolutionary hypotheses on the diversification patterns of parasites.…”

Circulation Pathways of Trematodes of Freshwater Gastropod Mollusks in Forest Biocenoses of the Ukrainian Polissia

“…Like other parasitic organisms, they negatively aff ect organisms, populations, animal groups and food chains in general (Kuris et al, 2008). Trematodes are internal parasites with a complex life cycle which includes a number of stages with parthenogenetic and amphimictic (mostly hermaphroditic) generations, as well as alternating hosts, invertebrates and vertebrates (Blasco-Costa, Poulin, 2017;Zhytova, Kornyushin, 2017). Th e fi rst intermediate host in that life cycle is almost always a molluscs (Serbina, 2014;Zhytova, Zhytov, 2016;Faltynkova, 2016;Gordy et al, 2016;Chontananarth, 2017), in which parthenogenetic generations of trematodes develop.…”

Genomics of host-pathogen interactions: challenges and opportunities across ecological and spatiotemporal scales

“…The most obvious illustration of this is variation in virulence associated with host switches: Mycoplasma infection in house finches as compared to other song birds (Ley et al, 2016), Ebola virus in humans as compared to bats (Leroy et al, 2005), or the morbillivirus Phocine Distemper Virus (PDV) in harbor seals as compared to other Arctic pinniped species (Härkönen et al, 2006) are all cases where virulence dramatically increased after switching to a new host. Second, another level of complexity presents itself in the cases of complex pathogen life cycles, where pathogens may require multiple host species for different developmental stages in order to complete their life cycle (Parker et al, 2003; Blasco-Costa & Poulin, 2017). In cases such as these, it is often difficult to differentiate between pathogen species and different pathogen life stages morphologically.…”