Angiostrongylus cantonensis in Introduced Gastropods in Southern Florida

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.

Potential intermediate hosts of Angiostrongylus cantonensis in the European Mediterranean region (Mallorca, Spain)

Angiostrongylus cantonensis is the main etiological agent of eosinophilic meningitis, a disease that often leads to severe neurological manifestations in mammals and birds. In recent years, the prevalence of this zoonotic nematode has dramatically increased as it expands into new territories beyond its native range in Southeast Asia and the Pacific Basin.Its arrival to Europe, the last continent to be invaded, has raised many questions concerning the parasite's life cycle, particularly in the Mediterranean region, where it is now endemic. This study aims to collect evidence about intermediate hosts (snail and slug species) involved in the transmission of the A. cantonensis in Mallorca. We have conducted a systematic surveillance of gastropods within 2 km radius areas, surrounding the specific locations where infected hedgehogs were found. We employed a sequence-based detection approach that included a species-specific PCR amplification followed by DNA sequencing of the internal transcribed spacer I (ITS-1). This conservative approach was essential to avoid cross reactions with the numerous metastrongylid species known to be circulating in Mallorca. Overall, we collected and identified 398 gastropods belonging to 17 species, of which 11% tested positive for A. cantonensis. These gastropods were collected from touristic settlements to agricultural lands. Five gastropod species: Theba pisana, Cornu aspersum, Deroceras reticulatum, Milax gagates and Otala lactea, had been previously incriminated as A. cantonensis intermediate hosts, while 6 species: Papillifera papillaris, Cochlicella acuta, Eobania vermiculata, Ganula lanuginosa, Milax nigricans and Rumina decollata, are newly recorded hosts. The findings of this study have important epidemiological implications, and further measures are discussed to prevent neuroangiostrongylosis cases.

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.

Angiostrongylus cantonensis (rat lungworm) in Florida, USA: current status

Angiostrongylus cantonensis has been found in Florida, USA, from the panhandle in the north to Miami and surrounding areas in the southern parts of the state, in both definitive and intermediate hosts in a limited studies completed in 2015. Additional studies have identified this parasite in a variety of intermediate hosts, both native and non-native gastropod species, with new host species recorded. Many areas in Florida with higher A. cantonensis prevalence were those with a high human population density, which suggests it is a matter of time before human infections occur in Florida. Case reports in the state currently involve non-human primates and include a gibbon and orangutan in Miami. Here, we report the current status of A. cantonensis in the state, as well as the infection in a capuchin monkey and presumptive infection in a red ruffed lemur in Gainesville, Florida.

Parasites and Parasitology in this SARS-CoV-2, COVID-19 World: An American Society of Parasitologists Presidential Address

The novel coronavirus disease 2019 (COVID-19) is one of the worst global health crises of this generation. The core of this pandemic is the rapid transmissibility of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, its high morbidity and mortality, and the presence of infectious asymptomatic carriers. As a result, COVID-19 has dominated this year's headlines and commanded significant research attention. As we consider SARS-CoV-2 and the COVID-19 pandemic, it is essential that scientists, governments, the media, and the general population also come to grips with the everyday cost of parasitic diseases. Plasmodium (malaria), schistosomes, filarial worms, hookworms, Ascaris, whipworms, and other protozoan and metazoan parasites take a tremendous toll on local communities. Yet, because most of these diseases are no longer endemic to developed countries, their research and intervention are not funded at levels that are proportional to their global morbidity and mortality. The scientific and public health communities must indeed vigorously fight SARS-CoV-2 and COVID-19, but while doing so and beyond, it will be essential to demonstrate steadfast resolve toward understanding and combating the parasitic diseases that for centuries have haunted humankind.

AcanR3990 qPCR: a novel, highly sensitive, bioinformatically-informed assay to detect Angiostrongylus cantonensis infections

BACKGROUND

Angiostrongylus cantonensis (Ac), or the rat lungworm, is a major cause of eosinophilic meningitis. Humans are infected by ingesting the 3 rd stage larvae from primary hosts, snails and slugs, or paratenic hosts. The currently used molecular test is a qPCR assay targeting the ITS1 rDNA region (ITS1) of Ac.

METHODS

In silico design of a more sensitive qPCR assay was performed based on tandem repeats predicted to be the most abundant by the RepeatExplorer algorithm. Genomic DNA (gDNA) of Ac were used to determine the analytical sensitivity and specificity of the best primer/probe combination. This assay was then applied to clinical and environmental samples.

RESULTS

The limit of detection of the best performing assay, AcanR3990, was 1 fg (the DNA equivalent of 1/100,000 dilution of a single 3 rd stage larvae). Out of 127 CDC archived CSF samples from varied geographic locations, the AcanR3990 qPCR detected the presence of Ac in 49/49 ITS1 confirmed angiostrongyliasis patients along with 15/73 samples previously negative by ITS1 qPCR despite strong clinical suspicion for angiostrongyliasis. Intermediate hosts (gastropods) and an accidental host, a symptomatic horse, were also tested with similar improvement in detection observed. AcanR3990 qPCR did not cross-react in five CSF from patients with proven neurocysticercosis, toxocariasis, gnathostomiasis and baylisascariasis. AcanR3990 qPCR failed to amplify genomic DNA from the other related Angiostrongylus species tested except for A. mackerrasae (Am), a neurotropic species limited to Australia that would be expected to present with a clinical syndrome indistinguishable from Ac.

CONCLUSION

These results suggest AcanR3990 qPCR assay is highly sensitive and specific with potential wide applicability as a One Health detection method for Ac and Am.

Gastropods as intermediate hosts of Angiostrongylus spp. in the Americas: bioecological characteristics and geographical distribution

BACKGROUND

Intermediate hosts are key organisms in maintaining parasite life cycles, because they can act as amplifiers in the transmission from natural reservoirs to humans. One of the most important groups of intermediate hosts for zoonotic nematode infections are gastropods,slugs and snails. These are essential organisms in the larval development of Angiostrongylus species.

OBJECTIVES

The objective of this paper is to review reports of Angiostrongylus spp. in naturally infected gastropods from the Americas, taking into account the diagnostic methods used in their identification, to be able to provide more accurate list of their intermediate hosts. We also discuss the factors that aid the dispersion of Angiostrongylus spp. in the Americas.

METHODS

This study reviews scientific publications and book sections on Angiostrongylus spp. in the Americas, including original works assessing larvae of Angiostrongylus in intermediate hosts. The eligible reports were classified accordingly to their geographical location, year of first record, and the larvae identification methodologies used. Digital repositories were used for the search. The bioecological characteristics of the main intermediate hosts are summarised.

FINDINGS

A total of 29 gastropod species that are naturally infected with Angiostrongylus spp. have been reported as intermediate hosts, 16 of which are land snails, two are freshwater snails, and 11 land slugs.

MAIN CONCLUSIONS

This study highlights the importance of integrative studies, analysing both the etiological agent and its transmission dynamic in the environment, the biological and ecological characteristics of the hosts, and the impact on host populations. It is necessary to increase interdisciplinary studies to determine the potential epidemiological health risk of angiostrongyliasis in the Americas, and thus be able to establish prevention, monitoring and contingency strategies in the region.

Prevalence of Angiostrongylus cantonensis among different species of snails in the village of Bagong Sikat Muñoz, Nueva Ecija, Philippines and its associated risk factors for zoonotic transmission

Snails are good source of protein and one of the delicacies in majority of the areas in the Philippines. However, they may act as an intermediate host for several parasites such as Angiostrongylus cantonensis. This parasite is commonly found in South East Asia especially in agricultural countries like the Philippines. Hence, the present study aims to determine the prevalence of A. cantonensis in their intermediate host in Village Bagong Sikat, which is situated at the rice granary of the Philippines. A total of 947 snails were randomly collected within 50 m × 50 m transect line through handpicked method. The third larvae (L3) stage from the snails was recovered through artificial tissue digestion. Results showed that 173 out of 947 snails (18.27%) were found positive with A. cantonensis L3 larvae. Three species of snails were recovered having Melanoides tuberculata to have the highest prevalence of A. cantonensis (21.54%) followed by Pomacea canaliculata (17.75%) and Vivipara angularis (17.74%). Statistical analysis further showed that prevalence of A. cantonensis and the length of snails has no significant difference (p > 0.05). The species of snails collected and found infected in the present study are considered part of the delicacies of the locals in Nueva Ecija. Thus, these results highlight the need to raise awareness of the locals regarding the zoonotic potential of A. cantonensis, which are of public health importance.

Species Identity and Size are Associated with Rat Lungworm Infection in Gastropods

Angiostrongylus cantonensis, the rat lungworm, is an emerging zoonotic pathogen that cycles between definitive rat and intermediate gastropod hosts. Zoonotic infection occurs when humans intentionally or accidentally consume infectious larvae in a gastropod host, and may manifest as neuroangiostrongyliasis, characterized by eosinophilic meningitis, severe neurological impairment, and even death. Thus, the risk of A. cantonensis zoonoses may be related to the distribution of A. cantonensis larvae across gastropod hosts. We screened 16 gastropod species from 14 communities on the island of O'ahu, Hawai'i, USA, to characterize the distribution of A. cantonensis among species and across host size. Prevalence (proportion of the population infected) and infection intensity (density of worms in host tissue) varied among gastropod species. Prevalence also varied with gastropod host size, but this relationship differed among host species. Most host species showed a positive increase in the probability of infection with host size, suggesting that within species relatively larger hosts had higher prevalence. The density of worms in an infected snail was unrelated to host size. These results suggest that variation in A. cantonensis infection is associated with demographic structure and composition of gastropod communities, which could underlie heterogeneity in the risk of human angiostrongyliasis across landscapes.

Eosinophilic meningitis due to Angiostrongylus cantonensis in Europe

OBJECTIVES

To describe and analyse the epidemiological and clinical characteristics of imported human angiostrongyliasis in Europe.

METHODS

A systematic literature review of cases of human angiostrongyliasis in Europe was performed. Seven databases were searched. The epidemiological and clinical characteristics were extracted from included records and simple summary statistics were performed on extracted data.

RESULTS

Twenty-two cases reported between 1988 and 2019 were identified. They were mainly from French Polynesia, Southeast Asia, and the Caribbean Islands. The dominant suspected mode of transmission was ingestion of prawns, shrimp, or salad. For patients with data, 90% had a history of headache, often lasting, and half had paresthesia. Eighty-nine percent had eosinophilia, 93% had cerebrospinal fluid (CSF) eosinophilia, and 92% had elevated CSF protein. Central nervous system (CNS) imaging was normal in most cases. Two-thirds received albendazole or mebendazole treatment, although this is not currently recommended.

CONCLUSIONS

We have increased previous numbers to 22 reported cases in total since 1988. Angiostrongyliasis should generally be suspected in patients with a lasting headache who have returned from Southeast Asia, China, the Caribbean Islands, Australia, or French Polynesia, as well as parts of North America and Tenerife, Spain, although one autochthonous case from mainland Europe has also been reported. A dietary history should focus on prawns, shrimp, and salad, whilst also including slugs and snails and other paratenic hosts where relevant. The clinical diagnosis is supported by the presence of blood eosinophilia, CSF eosinophilia, and elevated CSF protein. A definitive laboratory diagnosis should be sought, and CNS imaging should be used to support, not to rule out the diagnosis. The most up-to-date evidence should always be consulted before initiating treatment. Current recommendations include analgesics, corticosteroids, and periodic removal of CSF for symptom relief, while antihelminthic treatment is debated.

Angiostrongylus cantonensis Eosinophilic Meningitis in an Infant, Tennessee, USA

Angiostrongylus cantonensis, the rat lungworm, is the most common infectious cause of eosinophilic meningoencephalitis worldwide. This parasite is endemic to Southeast Asia and the Pacific Islands, and its global distribution is increasing. We report A. cantonensis meningoencephalitis in a 12-month-old boy in Tennessee, USA, who had not traveled outside of southwestern Tennessee or northwestern Mississippi.

Geographic distribution of Angiostrongylus cantonensis in wild rats (Rattus rattus) and terrestrial snails in Florida, USA

The parasitic nematode Angiostrongylus cantonensis is a major cause of eosinophilic meningitis in humans, and has been documented in other incidental hosts such as birds, horses, dogs and non-human primates. It is endemic in Hawaii, and there have been sporadic reports in the southern continental United States. This parasite uses rats as definitive hosts and snails as intermediate hosts. In this study, we collected potential definitive and intermediate hosts throughout Florida to ascertain the geographic distribution in the state: Rats, environmental rat fecal samples, and snails were collected from 18 counties throughout the state. Classical diagnostics and morphological identification, along with molecular techniques were used to identify nematode species and confirm the presence of A. cantonensis.

Of the 171 Rattus rattus collected, 39 (22.8%) were positive for A. cantonensis, and 6 of the 37 (16.2%) environmental rat fecal samples collected in three of the surveyed counties were also positive for this parasite by real time PCR. We examined 1,437 gastropods, which represented 32 species; 27 (1.9%) were positive for A. cantonensis from multiple sites across Florida. Three non-native gastropod species, Bradybaena similaris, Zachrysia provisoria, and Paropeas achatinaceum, and three native gastropod species, Succinea floridana, Ventridens demissus, and Zonitoides arboreus, which are newly recorded intermediate hosts for the parasite, were positive for A. cantonensis. This study indicates that A. cantonensis is established in Florida through the finding of adult and larval stages in definitive and intermediate hosts, respectively, throughout the state. The ability for this historically subtropical nematode to thrive in a more temperate climate is alarming, however as the climate changes and average temperatures rise, gastropod distributions will probably expand, leading to the spread of this parasite in more temperate areas. Through greater awareness of host species and prevalence of A. cantonensis in the United States, potential accidental infections may be avoided.

Evolution and Extinction of Land Snails on Oceanic Islands

Nonmarine molluscs are the major animal group with the greatest number of recorded extinctions due to anthropogenic impacts, and that number is certainly a serious underestimate. Land snails, particularly endemic land snails of oceanic islands, are the group of molluscs that have sustained the most extinctions. Understanding their ecology and the evolutionary processes that have led to their extreme vulnerability is crucial if we are to be able to conserve these diverse and important species. Oceanic island snails tend to have low α-diversity and high β-diversity, and divergence of habitat use among related species is known to occur in some radiations of land snails on oceanic islands. Processes of speciation and ecological interaction are possible major drivers of these patterns. The ecological opportunities available at the initial stage of insular evolution and the scarcity of effective predators may have led to divergence of habitat use and high β-diversity in oceanic island snails. Fewer and less diverse predators on oceanic islands lead to the evolution of fewer and less diverse defense traits in oceanic island snails, which results in their high vulnerability to non-native predators. High β-diversity of oceanic island snails also results in great vulnerability to habitat loss. Accordingly, the high susceptibility of oceanic island snails to extinction reflects their evolutionary history.

Cloning and expression of a 16-kDa recombinant protein from Angiostrongylus cantonensis for use in immunoblot diagnosis of human angiostrongyliasis

Angistrongylus cantonensis is a zoonotic nematode parasite and causative agent of human angiostrongyliasis, which clinically presents as eosinophilic meningitis or meningoencephalitis. Diagnosis of the disease is problematic since parasitologic findings are infrequent, and infection determinations must be based on the clinical symptoms and serological tests with limited specificities and sensitivities. The aim of the present study was to identify and generate a novel recombinant protein from A. cantonensis and evaluate its efficacy in the diagnosis of human angiostrongyliasis when incorporated into a Western blot serodiagnostic system. A cDNA protein expression library from adult A. cantonensis was constructed, followed by immunoscreening with serum from confirmed infected patients to identify and isolate immunoreactive clones. One clone, designated fAC40, possessed a partial sequence encoding a LisH protein domain with a predicted molecular weight of 16 kDa and containing four predicted antigenic peptides. By incorporating recombinant fAC40 in Western immunoblot tests using a serum panel consisting of confirmed and clinically diagnosed cases of human angiostrongyliasis and other helminthic infections, fAC40 exhibited a sensitivity and specificity of 91.8 and 100 %, respectively, and a positive and negative predictive value of 100 and 97.19 %, respectively, in the diagnosis of angiostrongyliasis. Importantly, it was not reactive with antibodies from serum of patients infected with Gnathostoma spinigerum and Cysticercus cellulosae, infections that clinically present neurological symptoms similar to angiostrongyliasis. These data demonstrate that the 16-kDa recombinant protein from A. cantonensis possesses high potential as a candidate antigen for a more sensitive and specific serodiagnosis of human angiostrongyliasis.

Angiostrongylus cantonensis: a review of its distribution, molecular biology and clinical significance as a human pathogen

Angiostrongylus cantonensis is a metastrongyloid nematode found widely in the Asia-Pacific region, and the aetiological agent of angiostrongyliasis; a disease characterized by eosinophilic meningitis. Rattus rats are definitive hosts of A. cantonensis, while intermediate hosts include terrestrial and aquatic molluscs. Humans are dead-end hosts that usually become infected upon ingestion of infected molluscs. A presumptive diagnosis is often made based on clinical features, a history of mollusc consumption, eosinophilic pleocytosis in cerebral spinal fluid, and advanced imaging such as computed tomography. Serological tests are available for angiostrongyliasis, though many tests are still under development. While there is no treatment consensus, therapy often includes a combination of anthelmintics and corticosteroids. Angiostrongyliasis is relatively rare, but is often associated with morbidity and sometimes mortality. Recent reports suggest the parasites' range is increasing, leading to fatalities in regions previously considered Angiostrongylus-free, and sometimes, delayed diagnosis in newly invaded regions. Increased awareness of angiostrongyliasis would facilitate rapid diagnosis and improved clinical outcomes. This paper summarizes knowledge on the parasites' life cycle, clinical aspects and epidemiology. The molecular biology of Angiostrongylus spp. is also discussed. Attention is paid to the significance of angiostrongyliasis in Australia, given the recent severe cases reported from the Sydney region.

The Increase of Exotic Zoonotic Helminth Infections: The Impact of Urbanization, Climate Change and Globalization

Zoonotic parasitic diseases are increasingly impacting human populations due to the effects of globalization, urbanization and climate change. Here we review the recent literature on the most important helminth zoonoses, including reports of incidence and prevalence. We discuss those helminth diseases which are increasing in endemic areas and consider their geographical spread into new regions within the framework of globalization, urbanization and climate change to determine the effect these variables are having on disease incidence, transmission and the associated challenges presented for public health initiatives, including control and elimination.

Gastropod-Borne Helminths: A Look at the Snail-Parasite Interplay

More than 300 million people suffer from a range of diseases caused by gastropod-borne helminths, predominantly flatworms and roundworms, whose life cycles are characterized by a diversified ecology and epidemiology. Despite the plethora of data on these parasites, very little is known of the fundamental biology of their gastropod intermediate hosts, or of the interactions occurring at the snail-helminth interface. In this article, we focus on schistosomes and metastrongylids of human and animal significance, and review current knowledge of snail-parasite interplay. Future efforts aimed at elucidating key elements of the biology and ecology of the snail intermediate hosts, together with an improved understanding of snail-parasite interactions, will aid to identify, plan, and develop new strategies for disease control focused on gastropod intermediate hosts.