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As training in helminthology has declined in the medical microbiology curriculum, many rare species of zoonotic cestodes have fallen into obscurity. Even among specialist practitioners, knowledge of human intestinal cestode infections is often limited to three genera, Taenia , Hymenolepis and Dibothriocephalus . However, five genera of uncommonly encountered zoonotic Cyclophyllidea ( Bertiella , Dipylidium , Raillietina , Inermicapsifer and Mesocestoides ) may also cause patent intestinal infections in humans worldwide. Due to the limited availability of summarized and taxonomically accurate data, such cases may present a diagnostic dilemma to clinicians and laboratories alike. In this review, historical literature on these cestodes is synthesized and knowledge gaps are highlighted. Clinically relevant taxonomy, nomenclature, life cycles, morphology of human-infecting species are discussed and clarified, along with the clinical presentation, diagnostic features and molecular advances, where available. Due to the limited awareness of these agents and identifying features, it is difficult to assess the true incidence of these ‘forgotten’ cestodiases as clinical misidentifications are likely to occur. Also, the taxonomic status of many of the human-infecting species of these tapeworms is unclear, hampering accurate species identification. Further studies combining molecular data and morphological observations are necessary to resolve these long-standing taxonomic issues and to elucidate other unknown aspects of transmission and ecology.

Background The cestode Dipylidium caninum is known to infect dogs via the ingestion of an intermediate flea host, typically Ctenocephalides felis . Simparica Trio ® is an oral combination drug product for dogs effective in the treatment and prevention of fleas, including C. felis . Here, we report two laboratory studies evaluating the efficacy of a single administration of Simparica Trio at the minimum label dosage of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin, and 5 mg/kg pyrantel (as pamoate salt) in preventing D. caninum infection in dogs for 1 month through killing of C. felis . Methods A total of 20 dogs ( n  = 10 per group) proven to be suitable hosts for C. felis were used in each of the two studies. Treatment occurred on day 0, with each dog given either the placebo or Simparica Trio. On days 0 (after treatment), 7, 14, 21, and 30, dogs were infested using 200 (± 5) unfed D. caninum -infected C. felis . Live flea counts were conducted on day 33 (72 ± 2 h after day 30 infestation). All dogs were euthanized on day 58, and each dog was necropsied for the recovery of D. caninum scolexes from the gastrointestinal tract. Results Placebo-treated dogs had adequate flea infestations and cestode infections in both studies. Simparica-Trio-treated dogs were free of fleas on day 33 (100% efficacy) and had significantly lower mean flea counts compared with placebo-treated dogs ( P  ≤ 0.0007). Scolex counts in Simparica-Trio-treated dogs were also significantly decreased compared with placebo-treated dogs in both studies. The efficacy of Simparica Trio against D. caninum based on least squares mean scolex counts was 100% ( P  < 0.0001) in study 1 and 92.1% ( P  = 0.0033) in study 2. Conclusions The efficacy provided by Simparica Trio against C. felis at the minimum dosage of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin, and 5 mg/kg pyrantel (as pamoate salt) prevented D. caninum infection in dogs for 1 month. Graphical Abstract

Background Revolution ® Plus is a topical combination drug product containing selamectin and sarolaner that has been proven effective against the cat flea Ctenocephalides felis , the intermediate host of the cestode Dipylidium caninum . Here, we report two studies evaluating the efficacy of a single administration of Revolution Plus in preventing D. caninum infection in cats for 1 month through killing of the flea intermediate host. Methods Two studies (study 1 and 2) with the same design were conducted. In both studies, 2 treatment groups of ten cats each were enrolled. On Day 0, the cats in group 1 were treated with a placebo, and the cats in group 2 were treated with Revolution Plus at the minimum recommended dose of 6.0 mg/kg selamectin and 1.0 mg/kg sarolaner. After treatment on Day 0, as well as on Days 7, 14, 21, and 30, the cats in both treatment groups were infested with 100 (± 5) unfed, D. caninum -infected fleas. Live flea counts were conducted on Day 33 (72 ± 2 h after Day 30 infestation). All cats were euthanized on Day 58, and necropsies were performed to enumerate D. caninum scolices in the gastrointestinal tract. Results In both study 1 and 2, all placebo-treated cats were infested with two or more D. caninum scolices at necropsy. Significantly lower mean flea counts were recorded for the Revolution Plus-treated cats compared with placebo-treated cats ( P  ≤ 0.0001), and efficacy based on least squares mean flea counts on Day 33 was 100% (in study 1) and 94.3% (in study 2). Scolex counts were also significantly decreased in Revolution Plus-treated cats compared with placebo-treated cats, with a 97.1% efficacy in study 1 and a 99.3% efficacy in study 2. Conclusions One topical administration of Revolution Plus at the minimum dosage of 6.0 mg/kg selamectin and 1.0 mg/kg sarolaner provided high efficacy in the prevention of D. caninum infection through the killing of its vector, C. felis , for an entire month. Graphical Abstract

The members of genus Moniezia are the common parasites of livestock in tropical areas. The tapeworm, Moniezia expansa is commonly found in the gastrointestinal tract of the small and large ruminants. The present study focused on reporting the prevalence of M . expansa in small ruminants of southern Punjab: sheep and goats, in relation with epidemiological factors like age and gender. An overall prevalence of 27.2% was estimated for the small ruminants with higher infection rates in males (29.8%) and younger age group (<1 year; 32.9%). Moreover, the molecular characterization and phylogenetic analysis of the isolates based on partial cox1 gene indicated the placement of these sequences in the M . expansa cluster. Two distinct haplotypes, without any host tropism, were identified within the Pakistani isolates. A meta-analysis for M . expansa was run for all available global reports exhibiting an overall pooled prevalence of 21.3% (CI 95%: 13.5–29.0). Additionally, a global dataset encompassing 59 partial cox1 sequences submitted from different geographical locations was also assessed. Moderate haplotype diversity (0.760 ± 0.051) and significantly negative deviations from neutrality were estimated. The median joining haplotype network for these sequences revealed an interesting population structure indicating highly divergent sequences from China and Iraq compared to Pakistan, India, Vietnam, Senegal and Ethiopia. Given inconsistencies in genetic data there is a dire need to carry out molecular studies across the entire distributional range of M . expansa to delineate genetic diversity and population structure of the species. This will also be crucial in reevaluating the taxonomy of genus Moniezia .

Dipylidium caninum is a common tapeworm of dogs. Two cases of praziquantel resistance have been described in D. caninum in the United States. No further reports have been published to the authors’ knowledge. Here, the case of a dog imported to Switzerland from Spain with a history of chronic excretion of tapeworm proglottids and unresponsiveness to praziquantel treatments is reported. Clinical signs were mild (restlessness, tenesmus, anal pruritus, squashy feces) and flea infestation could be ruled out. Infection with D. caninum was confirmed through morphological and genetic parasite identification. Different subsequently applied anthelmintic compounds and protocols, including epsiprantel, did not confer the desired effects. Proglottid shedding only stopped after oral mebendazole administration of 86.2 mg kg−1 body weight for 5 consecutive days. Clinical signs resolved and the dog remained coproscopically negative during a follow-up period of 10 months after the last treatment. This case represents the first reported apparent praziquantel and epsiprantel resistance in D. caninum in Europe. Treatment was extremely challenging especially due to the limited availability of efficacious alternative compounds.

Background Only 14 crowned sifaka ( Propithecus coronatus ), a critically endangered lemur species, are currently held in zoological institutions. Hydatigera kamiyai is a newly described cryptic species within the Hydatigera taeniaeformis complex. Case presentation A 3-year-old crowned sifaka presented with acute right hemiparesis. Magnetic resonance imaging exam revealed a two-centimetre diameter left thalamic mass with severe oedema, suggestive of an abscess. Intravenous antimicrobial therapy was initiated with metronidazole and trimethoprim-sulfamethoxypyridazine and continued for one month, as blood culture results were inconclusive. Clinical follow-up included unremarkable complete blood work and repeated MRI exams. The latter revealed an 80% reduction in the size of the mass, associated with full clinical recovery within 60 days. Because some tapeworms, such as Taenia martis , can cause nodular lesions in various locations in humans and non-human primates, a deworming treatment was implemented. Simultaneous immunological testing for hydatidosis and cysticercosis was strongly positive (ELISA, serum immunoglobulin G: 1.741). Oral praziquantel at 25 mg/kg led to severe lethargy after a single dose. Abdominal ultrasound under volatile general anaesthesia revealed two three-centimetre diameter heterogeneous hepatic cavitary structures containing linear hyperechoic elements, with a 0.8-centimetre-thick wall. Oral deworming treatment was readjusted and consisted in 15 days of praziquantel, followed by one-month of albendazole. Four months following the appearance of the first clinical signs, the animal suddenly became comatose and died despite intensive care. Post-mortem exam revealed multiple 12-centimetre-long pseudosegmented larvae (strobilocerci) within hepatic lesions. Brain histology revealed a resolving chronic abscess inconsistent with a parasitic aetiology. The larvae isolated in the liver were identified as Hydatigera kamiyai through morphological and molecular approaches. This cryptic species, belonging to the Hydatigera genus, most likely uses rodents as intermediate hosts and domestic cats as definitive hosts to complete its life cycle. Conclusion Based on a thorough literature review, this report is the first description of an infection by this cestode in a non-human primate. Non-human primates may serve as aberrant intermediate hosts for Hydatigera kamiyai , which raises concerns regarding its potential zoonotic risk. This case also underscores the importance of parasitological surveillance in zoological institutions and the relevance of One Health considerations.

Taenia multiceps is a taeniid cestode that inhabits the small intestines of both wild and domestic carnivores. The larval stage, Coenurus cerebralis , is typically found in the central nervous system (CNS) of a wide range of livestock and, to a lesser extent, in the extra-cerebral tissues of sheep and goats. This review covers all aspects of the life cycle of T. multiceps and its epidemiology, molecular characterization, pathogenesis, diagnosis, therapy, control and zoonotic potential. Coenurosis caused by the larval stage of T. multiceps has a worldwide distribution and is often fatal in intermediate hosts, which can result in substantial economic losses in livestock farming. Molecular characterization using the mitochondrial genes cytochrome c oxidase subunit 1 and nicotinamide adenine dinucleotide dehydrogenase subunit 1 of different T. multiceps populations has revealed significant genetic variation and the presence of three major haplotypes. The disease mostly affects young sheep and is referred to as either acute or chronic coenurosis. Acute coenurosis occurs as a result of oncospheres migrating through the CNS, while chronic coenurosis occurs as a consequence of the coenurus maturing, which causes displacement and pressure atrophy of brain tissue. Non-cerebral coenurosis has been most commonly reported in goats. The best diagnostic method for cerebral coenurosis involves the interpretation of clinical signs with accurate localization of the cyst using diagnostic imaging techniques. A vaccine based on recombinant oncosphere antigens has proved to be an effective tool against T. multiceps infection in sheep. Additionally, use of anthelmintics during the parasite’s migration stages reduces the development of cysts in the sheep brain. Surgery is considered the most effective method for the treatment of cerebral coenurosis in small ruminants, but is often not carried out because of the limited finances of many sheep and goat breeders. However, coenurosis can also be controlled effectively through preventative measures, such as anthelmintic treatment of dogs and the proper disposal of intermediate host carcasses. The parasite is also zoonotic, and cases of coenurosis have been reported in humans with coenuri located in the brain, spinal cord and eyes. Graphical abstract

Background Marine mammals act as sentinel species, with top predators’ overall health reflecting their ecosystem, integrated across multiple trophic levels. Yet apparently healthy wild animals may have significant subclinical pathology that goes undetected due to unknown medical histories. Marine mammals, particularly phocid seals, often suffer from heavy parasite burdens. While there are documented cases of severe respiratory infections resulting in complications during sedation, there have been no reports of gastrointestinal parasites contributing to poor outcomes during examinations requiring sedation or anesthesia. This report describes two unique presentations of high intestinal parasite loads that purportedly predisposed Weddell seals ( Leptonychotes weddellii ) to complications under sedation, and characterizes underlying pathology. Case presentation Two adult female Weddell seals exhibited prolonged apnea and vomiting while under intravenous sedation, that led to aspiration and mortality despite resuscitation attempts. Post-mortem examination revealed a severe Diphyllobothrium tapeworm impaction in the duodenum, with the parasitic mass causing a partial or complete obstruction. In both cases, the stomach was remarkably distended, suggesting the parasitic mass slowed gastric emptying. Both animals’ stomachs contained a high parasite burden with roundworms embedded into the mucosa. Histological analysis identified underlying pathological conditions that were likely parasite related, including chronic pneumonia associated with lungworm infestations, reactive, depleted and fibrosed lymph nodes, granulomatous lymphadenitis and hepatitis. Further examination in one of the animals revealed severe gastritis and necrotizing duodenitis at the site of the cestode infection. Conclusions To our knowledge, this is the first description of a significant gastrointestinal parasitic impaction being linked to acute distress during sedation in a marine mammal. We provide an in-situ depiction of the severe cestode infection. It is noteworthy that both animals in this case study exhibited histopathology consistent with chronic inflammation across multiple organ systems. Whether animals were sufficiently immunocompromised that rapid parasite growth became unchecked, or whether the parasite infestation led to dysfunction in other organs remains unresolved. We discuss the potential for premedication with prokinetic agents that increase esophageal sphincter tone to mitigate complications in future late-summer Weddell seal handlings.

Host-parasite interactions are ubiquitous and are important drivers of host diversification and evolution. In particular, host immune systems are frequent targets of parasite-driven selection. The resulting rapid evolution of immune genes is usually framed as an ongoing 'arms race' between a co-evolving pair of host and parasite species. However, immune evolution may often be driven by the acquisition of a new and unfamiliar parasite. For instance, when marine populations of threespine stickleback ( ) colonized freshwater lakes approximately 12,000 years ago, they encountered the freshwater-restricted cestode and evolved resistance. We compared the transcriptomic responses of lab-reared sticklebacks from three populations of stickleback with varying cestode susceptibilities when exposed to several immune stimuli (alum, cestode protein, or a control injection). The resulting changes in expression reveal strong evidence of shared and population-specific responses during the evolution of defense against a new parasite. Our investigation highlights the roles of several key immunological processes in underlying a general physiological response to tissue damage (fibrosis) and the importance of regulating fibrosis as a necessary step for its co-option into defense against tapeworms. Furthermore, we highlighted changes in the expression of fibrosis-associated genes, which facilitate faster and more targeted deployment of this defense mechanism against parasites. Fish from the most fibrosis-prone population exhibited constitutively higher expression of fibrosis-associated genes and stronger downregulation of these genes after an initial stimulus from injected cestode proteins. Our results provide strong evidence that changes in gene regulation and increased negative feedback to mitigate immunopathology are essential steps in the evolutionary co-option of an existing pathway to defend against a new parasite infection.

In China, frogs play an understudied role in the spread of human sparganosis (caused by the larval form of Spirometra). However, our knowledge about the prevalence of sparganum infection in frogs remains fragmented, and the taxonomic identification of the parasite is still controversial. The prevalence of sparganum infection in wild frogs was surveyed at 145 geographical locations from 28 of the 34 provinces/autonomous regions/municipalities in China for six years. The collected sparganum isolates from the different locations were subjected to molecular identification by a multiplex PCR assay and then were analysed with clustering analysis. In the survey, sparganum infection was found in 8 out of 13 of the collected frog species, and the most frequently infected species was Pelophylax nigromaculatus (the infection rate was up to 14.07%). Infected frogs were found in 80 of the 145 surveyed locations. The sparganum infection rates in the wild frogs in several regions of China were still high (above 10%), especially in South and Southwest China. A total of 72 spargana were selected for molecular identification, and the clustering analysis showed that sequences from the Chinese isolates were very similar to those identified as from Spirometra erinaceieuropaei. However, the taxonomy of the genus remains confused and further analysis is required. Eating wild frogs is associated with considerable health risks in China. Several traditional Chinese folk remedies may increase the risk of infection. The sparganum isolates in China are most likely from S. erinaceieuropaei, but new studies, especially comprehensive morphological analyses, are needed in the future.