Co-occurrence of Angiostrongylus malaysiensis and Angiostrongylus cantonensis DNA in cerebrospinal fluid: Evidence from human eosinophilic meningitis after ingestion of raw snail dish in Thailand

Severe angiostrongyliasis with neuropsychiatric symptoms in vulnerable adults: Early diagnosis via next-generation sequencing and successful treatment

Angiostrongylus cantonensis (AC) is a parasite that occasionally infects humans, causing eosinophilic meningitis (EM). In this study, we identified two adult males with severe angiostrongyliasis being treated at the ICU. Both presented with mental and behavioral abnormalities and were initially treated for psychiatric disorders before showing symptoms like cough, fever, and altered consciousness. Patient 1, a homeless individual, presented with elevated eosinophil levels and typical meningitis symptoms, prompting an early diagnosis of EM that was later confirmed via next-generation sequencing (NGS) of the cerebrospinal fluid. Patient 2, who had schizophrenia as a pre-existing condition, did not exhibit the typical signs of meningitis but was nonetheless detected via NGS. Both patients responded well to corticosteroids and anthelmintics. A review of case reports underscores heightened infection risks among children with pica and vulnerable adults, including those with mental disorders or homelessness. The use of NGS is effective for the early diagnosis and treatment of severe angiostrongyliasis, especially in those with atypical symptoms.

Evaluation of Enrichment Approaches for the Study of the Viromes in Mollusk Species

Invasive alien species such as freshwater snails have significantly affected the food, environment, and the health of humans and animals, which have unfortunately received insufficient attention. To facilitate the study of viromes in snail species, we compared the enrichment effect of cesium chloride (CsCl) and sucrose density gradient ultracentrifugations in the recovery of diverse viruses in Pomacea canaliculata and Achatina fulica. First, we showed that CsCl-based ultracentrifugation enriched more virus contigs and reduced the nucleic acid background of the Pomacea canaliculata and was thus beneficial for virus recovery. Further studies comparing CsCl- and sucrose-based density gradient ultracentrifugations revealed that the former enriched more viral contigs and viral families of RNA viruses, while the latter yielded more DNA viruses from both Pomacea canaliculata and Achatina fulica. Certain RNA virus families, such as Rhabdoviridae, Arenaviridae, Hepeviridae, Astroviridae, and Alphatetraviridae, were exclusively enriched by CsCl-based ultracentrifugation. Conversely, several DNA virus families including Bacilladnaviridae, Nudiviridae, Malacoherpesviridae, and Adintoviridae were solely identified using the sucrose-based method. Therefore, the selection of viral enrichment technique (either CsCl or sucrose density gradient ultracentrifugation) should be carefully considered based on the specific virome (DNA or RNA viruses) being studied in mollusk species.

Insights into the genetic diversity of Angiostrongylus spp. causing human angiostrongyliasis and implications for molecular identification and diagnosis

Angiostrongylus cantonensis and Angiostrongylus costaricensis are known human pathogens responsible for eosinophilic angiostrongyliasis and abdominal angiostrongyliasis, respectively. Humans are accidental hosts, where infection occurs through the consumption of the infective larva stage 3 in intermediate or paratenic hosts. The proven method for abdominal angiostrongyliasis diagnosis is the histological examination through tissue biopsy, while the diagnosis of eosinophilic angiostrongyliasis is the detection of larva in the cerebrospinal fluid. As there is molecular evidence of cryptic species within A. cantonensis and A. costaricensis lineages, along with morphological similarities within both lineages, accurate species identification and disease diagnosis may be challenging. Moreover, species within the lineages share similar intermediate and definitive hosts and geographic distribution. For example, both A. cantonensis and Angiostrongylus malaysiensis (a closely related species in A. cantonensis lineage) overlap in their geographic distribution in Southeast Asia. Additionally, variations in the molecular makeup of A. costaricensis and A. cantonensis lineages may impact the pathogenicity, infectivity, and disease severity of angiostrongyliasis. Understanding of the genetic diversity of both lineages is a cornerstone for improved diagnosis and disease intervention, especially in a changing global environment. To shed light and provide insights into the genetic diversity of the Angiostrongylus lineages causing human angiostrongyliasis, we aim to present an up-to-date review of the studies conducted and genetic markers used for A. costaricensis and A. cantonensis lineages. The implications for accurate molecular identification and diagnosis of human angiostrongyliasis are also discussed.

Paracapillaria (Ophidiocapillaria) siamensis sp. nov. (Nematoda: Trichuroidea): a new nematode in Naja kaouthia from Thailand

A comprehensive investigation, incorporating both morphological and molecular analyses, has unveiled the existence of a hitherto unknown nematode species, Paracapillaria (Ophidiocapillaria) siamensis sp. nov., residing in the intestine of the monocled cobra, Naja kaouthia, in the central region of Thailand. This study integrates morphological characteristics, morphometric examination, scanning electron microscopy and molecular phylogenetic analysis (COI, 18S rRNA and ITS1 genes). The findings place the newly described species within the subgenus Ophidiocapillaria, elucidating its distinctive characteristics, including a frame-like proximal spicule shape, approximate lengths of 19 000 and 22 500 μm with approximate widths of 90 and 130 μm for males and females, 39‒45 stichocytes, elevated lips without protrusion, a dorsal bacillary band stripe with an irregular pattern of bacillary cells and evidence of intestinal infection. These features serve to differentiate it from other species within the same subgenus, notably Paracapillaria (Ophidiocapillaria) najae De, , a species coexisting P. siamensis sp. nov. in the monocled cobra from the same locality. This study addresses the co-infection of the novel species and P. najae within the same snake host, marking the second documented instance of a paracapillariid species in the monocled cobra within the family Elapidae. The genetic characterization supports the formal recognition of P. siamensis sp. nov. as a distinct species, thereby underscoring its taxonomic differentiation within the Capillariidae family. This research identifies and characterizes the new nematode species, contributing valuable insights into the taxonomy of this nematode.

Molecular insights versus morphological traits: rethinking identification of the closely related Angiostrongylus cantonensis and Angiostrongylus malaysiensis

BACKGROUND

The closely related Angiostrongylus cantonensis and Angiostrongylus malaysiensis have been reported to coexist in Thailand and share similar hosts and life cycles. Recently, in an angiostrongyliasis outbreak in Thailand, both A. cantonensis and A. malaysiensis were found in the cerebrospinal fluid of affected patients. Morphological similarities, overlapping distribution, shared hosts and habitats, and the close genetics of the two Angiostrongylus species can complicate accurate species identification. Addressing these challenges, this study aims to evaluate whether a correlation between the morphological and genetic identities of A. cantonensis and A. malaysiensis can improve species identification accuracy.

METHODS

Angiostrongylus spp. specimens from five zoogeographical regions in Thailand were subjected to morphological and molecular identification using the mitochondrial cytochrome b gene and the nuclear internal transcribed spacer 2 region (ITS2). The morphological characters for males and females were then validated using the species identity obtained from the nuclear ITS2 region.

RESULTS

The results revealed that morphological misidentifications between these two closely related species are common due to overlapping morphological characters. Although certain male traits such as body length and width aided species differentiation, female traits were found to be less reliable. Furthermore, hybrid forms (8.2%) were revealed through the ITS2 results, which can further complicate morphological identification. Mito-nuclear discordance was also present in 1.9% of the Angiostrongylus specimens from Thailand, suggesting a complex historical interbreeding between the species.

CONCLUSIONS

Based on our findings, we suggest that nuclear ITS2 is a reliable marker for species identification of A. cantonensis and A. malaysiensis, especially in regions where both species coexist. Additionally, the scope and consequences of hybridization between the two closely related Angiostrongylus species should be further investigated in Thailand.

One-health approach on the future application of snails: a focus on snail-transmitted parasitic diseases

Snails are fascinating molluscs with unique morphological and physiological adaptive features to cope with various environments. They have traditionally been utilized as food and feed sources in many regions of the world. The future exploitation of alternative nutrient sources, like snails, is likely to increase further. Snails, however, also serve as an intermediate host for several zoonotic parasites. A category of parasitic infections, known as snail-transmitted parasitic diseases (STPDs), is harmful to humans and animals and is mainly driven by various trematodes, cestodes, and nematodes. The environment plays a crucial role in transmitting these parasites, as suitable habitats and conditions can facilitate their growth and proliferation in snails. In light of diverse environmental settings and biologically categorized snail species, this review evaluates the dynamics of significant STPDs of zoological importance. Additionally, possible diagnostic approaches for the prevention of STPDs are highlighted. One-health measures must be considered when employing snails as an alternative food or feed source to ensure the safety of snail-based products and prevent any adverse effects on humans, animals, and the environment.

A cross-sectional study of Angiostrongylus malaysiensis in rats and gastropod hosts from recreational parks in Kuala Lumpur, Malaysia: Detection, risk factors and pathology

Angiostrongylus malaysiensis is a potential zoonotic parasite, which reported to co-occur with A. cantonensis in human cerebrospinal fluid. It is a heteroxenous nematode that primarily develops through the early larval stages in gastropods and attains sexual maturity within rats. This study was conducted to determine the host species responsible for the reservoir of A. malaysiensis and investigate the risk factor for transmission among the hosts in Kuala Lumpur, Malaysia. Sampling was conducted in six recreational parks. The rats were trapped alive using steel wire traps with bait, while the gastropods were collected by active searching. The rats were euthanized and dissected to collect any adult worms observed. The molecular detection of A. malaysiensis was performed by PCR on gastropod tissue samples. Biotic and landscape factors were recorded for risk factor analysis. In total, 82 rats and 330 gastropods were collected throughout the study. Overall, 3.64% of gastropods and 32.9% of rats were infected with A. malaysiensis. Rattus tiomanicus (Malayan wood rat) and Parmarion martensi (Yellow-shelled semi-slug) were found as important hosts for A. malaysiensis. Host species, sampling site and macrohabitat type are risk factors associated with the prevalence of A. malaysiensis infection in rats. For gastropods, host species and sampling site are risk factors that correlate with the parasite detection. In total, 128 adult A. malaysiensis were recovered from the infected rats. The mean intensity of infection with adult A. malaysiensis was 4.65 for Rattus rattus complex and 4.90 for R. tiomanicus. Adult worms were found in the pulmonary artery or right ventricle, while eggs and first-stage larvae were found in capillaries of the caudal lung lobe. Infected lungs showed extravasated red blood cells in the alveolar spaces. The pulmonary arteries in the infected lung lobe were thickened. Kepong Metropolitan Park is the hotspot area for A. malaysiensis in Kuala Lumpur. These results provide essential information for public health officials to develop targeted interventions to reduce the transmission of A. malaysiensis in urban areas, particularly in recreational parks.

Identification and genetic characterization of Angiostrongylus cantonensis isolated from the human eye

Angiostrongylus cantonensis, or the rat lungworm, is the causative agent of human angiostrongyliasis associated with eosinophilic meningitis or meningoencephalitis. Additionally, this nematode can cause ocular angiostrongyliasis, though this is rare. The worm can cause permanent damage to the affected eye and sometimes even blindness. Genetic characterization of the worm from clinical samples is limited. In the present study, we investigated the genetics of A. cantonensis recovered from a patient's eye in Thailand. We sequenced two mitochondrial genes (cytochrome c oxidase subunit I, or COI, and cytochrome b, or cytb) and nuclear gene regions (66-kDa protein and internal transcribed spacer 2, or ITS2) from a fifth-stage larva of Angiostrongylus sample that was surgically removed from the human eye. All sequences of the selected nucleotide regions were highly similar (98-100%) to the sequences of A. cantonensis in the GenBank database. The maximum likelihood and neighbor-joining trees of the COI gene indicated that A. cantonensis was closely related to the AC4 haplotype, whereas the cytb and 66-kDa protein genes were closely clustered with the AC6 and Ac66-1 haplotypes, respectively. In addition, the phylogeny of the concatenated nucleotide datasets of the COI and cytb revealed that the worm was closely related to the Thai strain and strains from other countries. This study confirms the identification and genetic variation of the fifth-stage larvae of A. cantonensis recovered from a patient's eye in Thailand. Our findings are important for future research on the genetic variation of A. cantonensis that causes human angiostrongyliasis.

Comparative biology of parasitic nematodes in the genus Angiostrongylus and related genera

The rise to prominence of some Angiostrongylus species through associated emerging disease in humans and dogs has stimulated calls for a renewed focus on the biology of this genus and three related genera. Although significant research efforts have been made in recent years these have tended to focus on individual species and specific aspects such as diagnosis and treatment of disease or new records of occurrence and hosts. This comprehensive review takes a comparative approach, seeking commonalities and differences among species and asking such questions as: Which species belong to this and to closely related genera and how are they related? Why do only some species appear to be spreading geographically and what factors might underlie range expansion? Which animal species are involved in the life cycles as definitive, intermediate, paratenic and accidental hosts? How do parasite larvae find, infect and develop within these hosts? What are the consequences of infection for host health? How will climate change affect future spread and global health? Appreciating how species resemble and differ from each other shines a spotlight on knowledge gaps and provides provisional guidance on key species characteristics warranting detailed study. Similarities exist among species, including the basic life cycle and transmission processes, but important details such as host range, climatic requirements, migration patterns within hosts and disease mechanisms differ, with much more information available for A. cantonensis and A. vasorum than for other species. Nonetheless, comparison across Angiostrongylus reveals some common patterns. Historically narrow definitive host ranges are expanding with new knowledge, combining with very broad ranges of intermediate gastropod hosts and vertebrate and invertebrate paratenic and accidental hosts to provide the backdrop to complex interactions among climate, ecology and transmission that remain only partly understood, even for the species of dominant concern. Key outstanding questions concern larval dynamics and the potential for transmission outside trophic relations, relations between infection and disease severity in different hosts, and how global change is altering transmission beyond immediate impacts on development rate in gastropods. The concept of encounter and compatibility filters could help to explain differences in the relative importance of different gastropod species as intermediate hosts and determine the importance of host community composition and related environmental factors to transmission and range. Across the group, it remains unclear what, physiologically, immunologically or taxonomically, delimits definitive, accidental and paratenic hosts. Impacts of infection on definitive host fitness and consequences for population dynamics and transmission remain mostly unexplored across the genus. Continual updating and cross-referencing across species of Angiostrongylus and related genera is important to synthesise rapid advances in understanding of key traits and behaviours, especially in important Angiostrongylus species that are emerging causative agents of disease in humans and other animals.

An Overview of Angiostrongylus cantonensis (Nematoda: Angiostrongylidae), an Emerging Cause of Human Angiostrongylosis on the Indian Subcontinent

Human angiostrongylosis is an emerging zoonosis caused by the larvae of three species of metastrongyloid nematodes of the genus Angiostrongylus, with Angiostrongylus cantonensis (Chen, 1935) being dominant across the world. Its obligatory heteroxenous life cycle includes rats as definitive hosts, mollusks as intermediate hosts, and amphibians and reptiles as paratenic hosts. In humans, the infection manifests as Angiostrongylus eosinophilic meningitis (AEM) or ocular form. Since there is no comprehensive study on the disease in the Indian subcontinent, our study aims at the growing incidence of angiostrongylosis in humans, alongside its clinical course and possible causes. A systematic literature search revealed 28 reports of 45 human cases from 1966 to 2022; eosinophilic meningitis accounted for 33 cases (75.5%), 12 cases were reported as ocular, 1 case was combined, and 1 case was unspecified. The presumed source of infection was reported in 5 cases only. Importantly, 22 AEM patients reported a history of eating raw monitor lizard (Varanus spp.) tissues in the past. As apex predators, monitor lizards accumulate high numbers of L3 responsible for acute illness in humans. For ocular cases, the source was not identified. Most cases were diagnosed based on nematode findings and clinical pathology (primarily eosinophilia in the cerebrospinal fluid). Only two cases were confirmed to be A. cantonensis, one by immunoblot and the other by q-PCR. Cases of angiostrongylosis have been reported in Delhi, Karnataka, Kerala, Maharashtra, Madhya Pradesh, Puducherry, Telangana, and West Bengal. With a population of more than 1.4 billion, India is one of the least studied areas for A. cantonensis. It is likely that many cases remain undetected/unreported. Since most cases have been reported from the state of Kerala, further research may focus on this region. Gastropods, amphibians, and reptiles are commonly consumed in India; however, typical preparation methods involve cooking, which kills the nematode larvae. In addition to studying rodent and mollusk hosts, monitor lizards can be used as effective sentinels. Sequence data are urgently needed to answer the question of the identity of Angiostrongylus-like metastrongylid nematodes isolated from all types of hosts. DNA-based diagnostic methods such as q-PCR and LAMP should be included in clinical diagnosis of suspected cases and in studies of genetic diversity and species identity of nematodes tentatively identified as A. cantonensis.

The Global Spread Pattern of Rat Lungworm Based on Mitochondrial Genetics

Eosinophilic meningitis due to rat lungworm, Angiostrongylus cantonensis, is a global public health concern. Human cases and outbreaks have occurred in the new endemic areas, including South America and Spain. The growing genetic data of A. cantonensis provides a unique opportunity to explore the global spread pattern of the parasite. Eight more mitochondrial (mt) genomes were sequenced by the present study. The phylogeny of A. cantonensis by Bayesian inference showed six clades (I-VI) determined by network analysis. A total of 554 mt genomes or fragments, which represented 1472 specimens of rat lungworms globally, were used in the present study. We characterized the gene types by mapping a variety of mt gene fragments to the known complete mt genomes. Six more clades (I2, II2, III2, V2, VII and VIII) were determined by network analysis in the phylogenies of cox1 and cytb genes. The global distribution of gene types was visualized. It was found that the haplotype diversity of A. cantonensis in Southeast and East Asia was significantly higher than that in other regions. The majority (78/81) of samples beyond Southeast and East Asia belongs to Clade II. The new world showed a higher diversity of Clade II in contrast with the Pacific. We speculate that rat lungworm was introduced from Southeast Asia rather than the Pacific. Therefore, systematic research should be conducted on rat lungworm at a global level in order to reveal the scenarios of spread.

Genetic analysis of a 66-kDa protein-encoding gene of Angiostrongylus cantonensis and Angiostrongylus malaysiensis

The rat lungworm Angiostrongylus cantonensis is globally known to be the cause of oeosinophilic meningitis in humans. Another congener, Angiostrongylus malaysiensis, is closely related to A. cantonensis and has been described as a potential human pathogenic parasite. These 2 worms are similar in terms of life cycle, host range and morphological and genetic information. However, there are limited studies about their genetic diversity based on the 66-kDa protein-encoding gene. The objective of this study was to explore the 66-kDa protein sequence variation of A. cantonensis and A. malaysiensis collected from Thailand. Two adult and 53 third-stage larval specimens of Angiostrongylus from 4 geographic locations in Thailand were molecularly identified using the 66-kDa protein gene. The phylogenetic trees (Bayesian inference tree and maximum-likelihood tree) showed that Angiostrongylus formed a monophyletic clade with a clear separation between A. cantonensis and A. malaysiensis. The genetic distance between A. cantonensis and A. malaysiensis varies from 0.82 to 2.86%, with a total of 16 variable sites. The analysis of genetic diversity revealed 1 and 5 new haplotypes of A. cantonensis and A. malaysiensis, respectively, and showed genetic differences between the populations of A. cantonensis and A. malaysiensis. The haplotype networks of A. cantonensis and A. malaysiensis populations in Thailand are similar to those of populations in some countries, indicating the range expansion of genomic origin between populations in different areas. In conclusion, the 66-kDa protein gene was a good genetic marker for studying genetic diversity and discriminating between A. cantonensis and A. malaysiensis.

Paratenic hosts of Angiostrongylus cantonensis and their relation to human neuroangiostrongyliasis globally

The nematode parasite Angiostrongylus cantonensis (rat lungworm) has a complex life cycle involving rats (definitive hosts) and gastropods (intermediate hosts), as well as various paratenic hosts. Humans become infected and develop rat lungworm disease (neuroangiostrongyliasis) when they consume intermediate or paratenic hosts containing the infective parasite larvae. This study synthesizes knowledge of paratenic hosts of A. cantonensis and investigates their role in causing human neuroangiostrongyliasis worldwide. A literature review was conducted by searching PubMed, JSTOR and Scopus, pooling additional information from sources accumulated over many years by RHC, and snowball searching. The review identified 138 relevant articles published between 1962 and 2022. Freshwater prawns/shrimp, crayfish, crabs, flatworms, fish, sea snakes, frogs, toads, newts, lizards, centipedes, cattle, pigs and snails were reported to act as paratenic hosts in various regions including South and Southeast Asia, Pacific islands, the USA and the Caribbean, as well as experimentally. Human cases of neuroangiostrongyliasis have been reported from the 1960s onwards, linked, sometimes speculatively, to consumption of freshwater prawns/shrimp, crabs, flatworms, fish, frogs, toads, lizards and centipedes. The potential of paratenic hosts to cause neuroangiostrongyliasis depends on whether they are eaten, how frequently they are consumed, the preparation method, including whether eaten raw or undercooked, and whether they are consumed intentionally or accidentally. It also depends on infection prevalence in the host populations and probably on how high the parasite load is in the consumed hosts. To prevent human infections, it is crucial to interrupt the transmission of rat lungworm to humans, from both intermediate hosts and frequently consumed paratenic hosts, by adhering to safe food preparation protocols. Educating the general public and the medical community about this largely neglected tropical/subtropical disease is key.

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Neuroangiostrongyliasis, an emerging parasitic disease of humans and wildlife.

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Caused by the nematode Angiostrongylus cantonensis (rat lungworm).

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Infection primarily via ingestion of stage 3 larvae of the parasite.

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People eat raw intermediate or paratenic hosts infected with stage 3 larvae.

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Comprehensive review of paratenic hosts’ role in neuroangiostrongyliasis globally.

An annotated checklist of the eukaryotic parasites of humans, exclusive of fungi and algae

The classification of "parasites" in the medical field is a challenging notion, a group which historically has included all eukaryotes exclusive of fungi that invade and derive resources from the human host. Since antiquity, humans have been identifying and documenting parasitic infections, and this collective catalog of parasitic agents has expanded considerably with technology. As our understanding of species boundaries and the use of molecular tools has evolved, so has our concept of the taxonomy of human parasites. Consequently, new species have been recognized while others have been relegated to synonyms. On the other hand, the decline of expertise in classical parasitology and limited curricula have led to a loss of awareness of many rarely encountered species. Here, we provide a comprehensive checklist of all reported eukaryotic organisms (excluding fungi and allied taxa) parasitizing humans resulting in 274 genus-group taxa and 848 species-group taxa. For each species, or genus where indicated, a concise summary of geographic distribution, natural hosts, route of transmission and site within human host, and vectored pathogens are presented. Ubiquitous, human-adapted species as well as very rare, incidental zoonotic organisms are discussed in this annotated checklist. We also provide a list of 79 excluded genera and species that have been previously reported as human parasites but are not believed to be true human parasites or represent misidentifications or taxonomic changes.