Canine neural angiostrongylosis: a case-control study in Sydney dogs

Rat lungworm (Angiostrongylus cantonensis) active larval emergence from deceased bubble pond snails (Bullastra lessoni) into water

Angiostrongylus cantonensis (the rat lungworm) is a zoonotic parasite of non-permissive accidental (dogs, humans, horses, marsupials, birds) hosts. The 3rd stage larvae (L3s) in the intermediate host (molluscs) act as the source of infection for accidental hosts through ingestion. Larvae can spontaneously emerge from dead gastropods (slugs and snails) in water, which are experimentally infective to rats. We sought to identify the time when infective A. cantonensis larvae can autonomously leave dead experimentally infected Bullastra lessoni snails. The proportion of A. cantonensis larvae that emerge from crushed and submerged B. lessoni is higher in snails 62 days post-infection (DPI) (30.3%). The total larval burden of snails increases at 91 DPI, indicating that emerged larvae subsequently get recycled by the population. There appears to be a window of opportunity between 1 and 3 months for infective larvae to autonomously escape dead snails. From a human and veterinary medicine viewpoint, the mode of infection needs to be considered; whether that be through ingestion of an infected gastropod, or via drinking water contaminated with escaped larvae.

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.

Host transmission dynamics of first- and third-stage Angiostrongylus cantonensis larvae in Bullastra lessoni

Given the importance of angiostrongyliasis as an emerging infectious disease of humans, companion animals, and wildlife, the current study focused on the transmission dynamics of first- and third-stage larvae of the parasitic nematode, Angiostrongylus cantonensis. The migration of infective larvae and their subsequent distribution within the Lymnaeidae snail, Bullastra lessoni, were investigated over time using microscopic examination of histological sections and fresh tissue. Snails were divided into four anatomical regions: (i) anterior and (ii) posterior cephalopedal masses, (iii) mantle skirt and (iv) visceral mass. The viability of free-swimming third-stage larvae, after their release from snail tissues, was evaluated in vitro by propidium iodide staining and infectivity by in vivo infection of Wistar rats. Snails were sequentially dissected over time to assess the number and anatomical distribution of larvae within each snail and hence infer their migration pathway. Herein, ongoing larval migratory activity was detected over 28 days post-infection. A comparison of infection rates and the larval distribution within the four designated snail regions demonstrated a significant relationship between anatomical region and density of infective larvae, with larvae mostly distributed in the anterior cephalopedal mass (43.6 ± 10.8%) and the mantle skirt (33.0 ± 8.8%). Propidium iodide staining showed that free-swimming third-stage larvae retained viability for between 4 and 8 weeks when stored under laboratory conditions. In contrast to viability, larval infectivity in rats remained for up to 2 weeks only. Knowledge gained from the current work could provide information on the development of new approaches to controlling the transmission of this parasite.

Pathology of Angiostrongylus cantonensis infection in two model avian hosts

Angiostrongylus cantonensis causes severe neurological disorders in a wide range of warm-blooded animals, including several avian species. A laboratory isolate of A. cantonensis originating from French Polynesia, genotyped as clade 2, was used to assess the effect of experimental infection in chicken and Japanese quail. Low dose groups of birds were infected orally by 100 L3 larvae, high dose groups by 1500 L3 larvae and the birds in the third group were fed three infected snails, mimicking a natural infection. Clinical signs during the first week after infection, haematology, biochemistry, gross lesions and histology findings were used to assess the pathology of the infection. Some of the infected birds showed peripheral eosinophilia, while mild neurological signs were seen in others. No larvae were observed in serial sections of the central nervous system of infected birds 1 week after infection and no major gross lesions were observed during necropsy; histopathology did not reveal lesions directly attributable to A. cantonensis infection. Our results suggest that galliform birds are not highly susceptible to A. cantonensis infection and open a question of the importance of Galliformes in endemic areas as natural pest control, lowering the number of hosts carrying the infective larvae.

Further studies of neuroangiostrongyliasis (rat lungworm disease) in Australian dogs: 92 new cases (2010-2020) and results for a novel, highly sensitive qPCR assay

The principal aim of this study was to optimize the diagnosis of canine neuroangiostrongyliasis (NA). In total, 92 cases were seen between 2010 and 2020. Dogs were aged from 7 weeks to 14 years (median 5 months), with 73/90 (81%) less than 6 months and 1.7 times as many males as females. The disease became more common over the study period. Most cases (86%) were seen between March and July. Cerebrospinal fluid (CSF) was obtained from the cisterna magna in 77 dogs, the lumbar cistern in f5, and both sites in 3. Nucleated cell counts for 84 specimens ranged from 1 to 146 150 cells μL-1 (median 4500). Percentage eosinophils varied from 0 to 98% (median 83%). When both cisternal and lumbar CSF were collected, inflammation was more severe caudally. Seventy-three CSF specimens were subjected to enzyme-linked immunosorbent assay (ELISA) testing for antibodies against A. cantonensis; 61 (84%) tested positive, titres ranging from <100 to ⩾12 800 (median 1600). Sixty-one CSF specimens were subjected to real-time quantitative polymerase chain reaction (qPCR) testing using a new protocol targeting a bioinformatically-informed repetitive genetic target; 53/61 samples (87%) tested positive, CT values ranging from 23.4 to 39.5 (median 30.0). For 57 dogs, it was possible to compare CSF ELISA serology and qPCR. ELISA and qPCR were both positive in 40 dogs, in 5 dogs the ELISA was positive while the qPCR was negative, in 9 dogs the qPCR was positive but the ELISA was negative, while in 3 dogs both the ELISA and qPCR were negative. NA is an emerging infectious disease of dogs in Sydney, Australia.

Low diversity of Angiostrongylus cantonensis complete mitochondrial DNA sequences from Australia, Hawaii, French Polynesia and the Canary Islands revealed using whole genome next-generation sequencing

Background

Rats (Rattus spp.) invaded most of the world as stowaways including some that carried the rat lungworm, Angiostrongylus cantonensis, the cause of eosinophilic meningoencephalitis in humans and other warm-blooded animals. A high genetic diversity of A. cantonensis based on short mitochondrial DNA regions is reported from Southeast Asia. However, the identity of invasive A. cantonensis is known for only a minority of countries. The affordability of next-generation sequencing for characterisation of A. cantonensis genomes should enable new insights into rat lung worm invasion and parasite identification in experimental studies.

Methods

Genomic DNA from morphologically verified A. cantonensis (two laboratory-maintained strains and two field isolates) was sequenced using low coverage whole genome sequencing. The complete mitochondrial genome was assembled and compared to published A. cantonensis and Angiostrongylus malaysiensis sequences. To determine if the commonly sequenced partial cox1 can unequivocally identify A. cantonensis genetic lineages, the diversity of cox1 was re-evaluated in the context of the publicly available cox1 sequences and the entire mitochondrial genomes. Published experimental studies available in Web of Science were systematically reviewed to reveal published identities of A. cantonensis used in experimental studies.

Results

New A. cantonensis mitochondrial genomes from Sydney (Australia), Hawaii (USA), Canary Islands (Spain) and Fatu Hiva (French Polynesia), were assembled from next-generation sequencing data. Comparison of A. cantonensis mitochondrial genomes from outside of Southeast Asia showed low genetic diversity (0.02–1.03%) within a single lineage of A. cantonensis. Both cox1 and cox2 were considered the preferred markers for A. cantonensis haplotype identification. Systematic review revealed that unequivocal A. cantonensis identification of strains used in experimental studies is hindered by absence of their genetic and geographical identity.

Conclusions

Low coverage whole genome sequencing provides data enabling standardised identification of A. cantonensis laboratory strains and field isolates. The phenotype of invasive A. cantonensis, such as the capacity to establish in new territories, has a strong genetic component, as the A. cantonensis found outside of the original endemic area are genetically uniform. It is imperative that the genotype of A. cantonensis strains maintained in laboratories and used in experimental studies is unequivocally characterised.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3491-y) contains supplementary material, which is available to authorized users.

Comparative pathogenesis of eosinophilic meningitis caused by Angiostrongylus mackerrasae and Angiostrongylus cantonensis in murine and guinea pig models of human infection

This study investigated comparatively the pathogenicity of experimental infection of mice and guinea pigs, with Angiostrongylus mackerrasae and the closely related species A. cantonensis. Time course analyses showed that A. mackerrasae causes eosinophilic meningitis in these hosts, which suggests that the species has the potential to cause meningitis in humans and domestic animals. Both A. mackerrasae and the genetically similar A. cantonensis caused eosinophilic meningitis in mice at two time points of 14 and 21 days post infection (dpi). The brain lesions in mice infected with A. mackerrasae were more granulomatous in nature and the parasites were more likely to appear degenerate compared with lesions caused by A. cantonensis. This may indicate that the mouse immune system eliminates A. mackerrasae infection more effectively. The immunologic responses of mice infected with the two Angiostrongylus species was compared by assessing ex vivo stimulated spleen derived T cells and cytokines including interferon-gamma, interleukin 4 and interleukin 17 on 14 and 21 dpi. The results were similar for mice infected with A. cantonensis and A. mackerrasae. Serum from the infected animals with either A. cantonensis or A. mackerrasae recognized total soluble antigen of A. cantonensis female worms on Western blot.

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 mitochondrial genome of Angiostrongylus mackerrasae as a basis for molecular, epidemiological and population genetic studies

Background

Angiostrongylus mackerrasae is a metastrongyloid nematode endemic to Australia, where it infects the native bush rat, Rattus fuscipes. This lungworm has an identical life cycle to that of Angiostrongylus cantonensis, a leading cause of eosinophilic meningitis in humans. The ability of A. mackerrasae to infect non-rodent hosts, specifically the black flying fox, raises concerns as to its zoonotic potential. To date, data on the taxonomy, epidemiology and population genetics of A. mackerrasae are unknown. Here, we describe the mitochondrial (mt) genome of A. mackerrasae with the aim of starting to address these knowledge gaps.

Methods

The complete mitochondrial (mt) genome of A. mackerrasae was amplified from a single morphologically identified adult worm, by long-PCR in two overlapping amplicons (8 kb and 10 kb). The amplicons were sequenced using the MiSeq Illumina platform and annotated using an in-house pipeline. Amino acid sequences inferred from individual protein coding genes of the mt genomes were concatenated and then subjected to phylogenetic analysis using Bayesian inference.

Results

The mt genome of A. mackerrasae is 13,640 bp in size and contains 12 protein coding genes (cox1-3, nad1-6, nad4L, atp6 and cob), and two ribosomal RNA (rRNA) and 22 transfer RNA (tRNA) genes.

Conclusions

The mt genome of A. mackerrasae has similar characteristics to those of other Angiostrongylus species. Sequence comparisons reveal that A. mackerrasae is closely related to A. cantonensis and the two sibling species may have recently diverged compared with all other species in the genus with a highly specific host selection. This mt genome will provide a source of genetic markers for explorations of the epidemiology, biology and population genetics of A. mackerrasae.