Dose-dependent impact of larval Ascaris suum on host body weight in the mouse model

Transient Ascaris suum larval migration induces intractable chronic pulmonary disease and anemia in mice

Ascariasis is one of the most common infections in the world and associated with significant global morbidity. Ascaris larval migration through the host’s lungs is essential for larval development but leads to an exaggerated type-2 host immune response manifesting clinically as acute allergic airway disease. However, whether Ascaris larval migration can subsequently lead to chronic lung diseases remains unknown. Here, we demonstrate that a single episode of Ascaris larval migration through the host lungs induces a chronic pulmonary syndrome of type-2 inflammatory pathology and emphysema accompanied by pulmonary hemorrhage and chronic anemia in a mouse model. Our results reveal that a single episode of Ascaris larval migration through the host lungs leads to permanent lung damage with systemic effects. Remote episodes of ascariasis may drive non-communicable lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and chronic anemia in parasite endemic regions.

Ascariasis is the most common helminth infection and leads to significant global morbidity. Transient Ascaris larval migration through the host’s lungs is essential for larval development but leads to an exaggerated type-2 host immune response. Our work demonstrates that transient Ascaris spp. larval migration through the lungs has significant long-term consequences including changes in lung structure and function as well as vascular damage causing chronic lung disease and anemia. We propose that Ascaris spp. larval migration through the host lungs is a risk factor for the development of chronic lung disease and anemia in parasite-endemic regions globally.

The long and winding road of Ascaris larval migration: the role of mouse models

Ascaris lumbricoides and Ascaris suum are helminth parasites of humans and pigs, respectively. The life cycle of Ascaris sets it apart from the other soil-transmitted helminths because of its hepato-tracheal migration. Larval migration contributes to underestimated morbidity in humans and pigs. This migration, coupled with a lack of a murine model in which the Ascaris parasite might complete its life cycle, has undoubtedly contributed to the neglected status of the ascarid. Our knowledge of the epidemiology of adult worm infections had led us to an enhanced understanding of patterns of infection such as aggregation and predisposition; however, the mechanisms underlying these complex phenomena remain elusive. Carefully controlled experiments in defined inbred strains of mice – with enhanced recovery of larvae in tandem with measurements of cellular, histopathological and molecular processes – have greatly enhanced our knowledge of the early phase of infection, a phase crucial to the success or failure of adult worm establishment. Furthermore, the recent development of a mouse model of susceptibility and resistance, with highly consistent and diverging Ascaris larval burdens in the murine lungs, represents the extremes of the host phenotype displayed in the aggregated distribution of worms and provides an opportunity to explore the mechanistic basis that confers predisposition to light and heavy Ascaris infection. Certainly, detailed knowledge of the cellular hepatic and pulmonary responses at the molecular level can be accrued from murine models of infection and, once available, may enhance our ability to develop immunomodulatory therapies to elicit resistance to infection.

Whipworm and roundworm infections

Trichuriasis and ascariasis are neglected tropical diseases caused by the gastrointestinal dwelling nematodes Trichuris trichiura (a whipworm) and Ascaris lumbricoides (a roundworm), respectively. Both parasites are staggeringly prevalent, particularly in tropical and subtropical areas, and are associated with substantial morbidity. Infection is initiated by ingestion of infective eggs, which hatch in the intestine. Thereafter, T. trichiura larvae moult within intestinal epithelial cells, with adult worms embedded in a partially intracellular niche in the large intestine, whereas A. lumbricoides larvae penetrate the gut mucosa and migrate through the liver and lungs before returning to the lumen of the small intestine, where adult worms dwell. Both species elicit type 2 anti-parasite immunity. Diagnosis is typically based on clinical presentation (gastrointestinal symptoms and inflammation) and the detection of eggs or parasite DNA in the faeces. Prevention and treatment strategies rely on periodic mass drug administration (generally with albendazole or mebendazole) to at-risk populations and improvements in water, sanitation and hygiene. The effectiveness of drug treatment is very high for A. lumbricoides infections, whereas cure rates for T. trichiura infections are low. Novel anthelminthic drugs are needed, together with vaccine development and tools for diagnosis and assessment of parasite control in the field.

Community Rates of IgG4 Antibodies to Ascaris Haemoglobin Reflect Changes in Community Egg Loads Following Mass Drug Administration

Background

Conventional diagnostic methods for human ascariasis are based on the detection of Ascaris lumbricoides eggs in stool samples. However, studies of ascariasis in pigs have shown that the prevalence and the number of eggs detected in the stool do not correlate well with exposure of the herd to the parasite. On the other hand, an ELISA test measuring antibodies to Ascaris suum haemoglobin (AsHb) has been shown to be useful for estimating transmission intensity on pig farms. In this study, we further characterized the AsHb antigen and screened samples from a population-based study conducted in an area that is endemic for Ascaris lumbricoides in Indonesia to assess changes in AsHb antibody rates and levels in humans following mass drug administration (MDA).

Methodology/Principal findings

We developed and evaluated an ELISA to detect human IgG4 antibodies to AsHb. We tested 1066 plasma samples collected at different times from 599 subjects who lived in a village in rural Indonesia that was highly endemic for ascariasis. The community received 6 rounds of MDA for lymphatic filariasis with albendazole plus diethylcarbamazine between 2002 and 2007. While the AsHb antibody assay was not sensitive for detecting all individuals with Ascaris eggs in their stools, the percentage of seropositive individuals decreased rapidly following MDA. Reductions in antibody rates reflected decreased mean egg output per person both at the community level and in different age groups. Two years after the last round of MDA the community egg output and antibody prevalence rate were reduced by 81.6% and 78.9% respectively compared to baseline levels.

Conclusion/Significance

IgG4 antibody levels to AsHb appear to reflect recent exposure to Ascaris. The antibody prevalence rate may be a useful indicator for Ascaris transmission intensity in communities that can be used to assess the impact of control measures on the force of transmission.

Ascariasis is a neglected tropical disease caused by the intestinal nematode Ascaris lumbricoides that affects hundreds of millions of people in the developing world. Current methods for diagnosis of this infection are based on detecting eggs in the stool that are excreted by adult Ascaris worms. However, these methods have limited sensitivity for recent infections, and they do not detect infections with immature parasite stages that do not always result in the establishment of adult worms in the human intestine. We have previously shown that an assay for antibodies to Ascaris hemoglobin in pig serum is useful for assessing transmission of Ascaris infections on pig farms. In this study, we developed and evaluated a similar antibody assay that is based on the detection of human IgG4 antibodies to Ascaris haemoglobin (AsHb). Community antibody rates decreased rapidly following mass drug administration of the anthelmintic drug albendazole, and this decrease reflected reduced Ascaris egg excretion at the community level. This antibody test may be a useful tool for assessing the impact of control measures on the transmission of new Ascaris infections in endemic populations.

Comparative profiling of microRNAs in male and female adults of Ascaris suum

Ascaris nematodes, which cause ascariasis in humans and pigs, are among the most important nematodes from both health and economic perspectives. microRNA (miRNA) is now recognized as key regulator of gene expression at posttranscription level. The public availability of the genome and transcripts of Ascaris suum provides powerful resources for the research of miRNA profiles of the parasite. Therefore, we investigated and compared the miRNA profiles of male and female adult A. suum using Solexa deep sequencing combined with bioinformatic analysis and stem-loop reverse transcription polymerase chain reaction. Deep sequencing of small RNAs yielded 11.71 and 11.72 million raw reads from male and female adults of A. suum, respectively. Analysis showed that the noncoding RNA of the two genders, including tRNA, rRNA, snRNA, and snoRNA, were similar. By mapping to the A. suum genome, we obtained 494 and 505 miRNA candidates from the female and male parasite, respectively, and 87 and 82 of miRNA candidates were consistent with A. suum miRNAs deposited in the miRBase database. Among the miRNA candidates, 154 were shared by the two genders, and 340 and 351 were female and male specific with their target numbers ranged from one to thousands, respectively. Functional prediction revealed a set of elongation factors, heat shock proteins, and growth factors from the targets of gender-specific miRNAs, which were essential for the development of the parasite. Moreover, major sperm protein and nematode sperm cell motility protein were found in targets of the male-specific miRNAs. Ovarian message protein was found in targets of the female-specific miRNAs. Enrichment analysis revealed significant differences among Gene Ontology terms of miRNA targets of the two genders, such as electron carrier and biological adhesion process. The regulating functions of gender-specific miRNAs was therefore not only related to the fundamental functions of cells but also were essential to the germ development of the parasite. The present study provides a framework for further research of Ascaris miRNAs, and consequently leads to the development of potential nucleotide vaccines against Ascaris of human and animal health significance.

Ascaris and ascariasis

Ascaris lumbricoides and Ascaris suum are widespread parasitic nematodes of humans and pigs respectively. Recent prevalence data suggests that approximately 1.2 billion people are infected. Adult worms exhibit an overdispersed frequency distribution in their hosts and individuals harbouring heavy burdens display associated morbidity. In this review, we describe the parasite, its distribution and measures undertaken to control infection.