Two cases of neuroangiostrongyliasis: A rare disease because rarely considered or rarely diagnosed?

AIM: The rat lungworm, Angiostrongylus cantonensis, is well established in eastern Australia, where it is the almost exclusive cause of human eosinophilic meningoencephalitis (EME). While neuroangiostrongyliasis can result in severe morbidity or death, its diagnosis requires a high index of clinical suspicion among medical practitioners. Prevention requires a high level of public awareness. METHODS: We report two cases of EME in children from Queensland and summarise all reported Australian cases from the literature. We discuss the pathogenesis of neuroangiostrongyliasis, with particular reference to the timing of prophylaxis and treatment. RESULTS: A 5-year-old girl developed severe headache, eosinophilic meningitis and abnormal neuroimaging following a holiday to Bali. A 10-year-old boy with Rubinstein-Taybi syndrome, marked developmental delay and pica developed EME following ingestion of a snail, resulting in long-term morbidity. From 1971 to 2018, 28 Australian cases have been reported, with acquisition restricted to Southeast Queensland and New South Wales. Ages ranged from 10 months to 45 years; most were male and most likely acquired infection from consuming unwashed lettuce or vegetables. The mortality rate was 18%; most fatalities occurred in children <1 year old. Long-term neurological deficit was reported in 14% of cases and a full recovery in 57% of cases. CONCLUSIONS: Heightened medical and public awareness of the parasite is required to prevent infection and subsequent disease. A better understanding of the efficacy of prophylactic anthelmintic following ingestion or handling of molluscs and further studies of epidemiology of this parasite will inform and facilitate public health recommendations.

Neuroangiostrongyliasis: The "Subarachnoid Phase" and Its Implications for Anthelminthic Therapy.

Infection with the Rat Lungworm Angiostrongylus cantonensis is the leading cause of human eosinophilic meningoencephalitis worldwide. From its origins in southeastern Asia, the parasite was spread extensively throughout the twentieth century and is now established in many of the world's warmer regions. Its clinical effects range from mild and transient symptoms, usually headache with peripheral nerve dysfunction, to severe and permanent central nervous system (CNS) damage, occasionally fatal. The severity and prognosis of disease are determined by the larval dose, acquired by ingesting infected intermediate hosts (slugs and snails) or, less often, paratenic hosts, such as crabs, shrimps, frogs, and monitor lizards. Early diagnosis is critical for treatment and depends on clinical suspicion, for laboratory confirmation from blood and cerebrospinal fluid can be delayed and unreliable. Treatment is fraught with difficulty, compounded by conflicting published results. Corticosteroids play a useful role in suppressing early CNS inflammation, but their duration for maintenance becomes problematic in severe infections. Because most of the pathogenesis results from host immuno-inflammatory responses to migrating and dead larvae in the CNS, anthelminthic therapy remains controversial: if effective, it kills viable larvae, arresting them in the CNS and so exacerbating the pathology. In human infections, it is now clear that many larvae do leave the CNS and reach the pulmonary arteries, sometimes with clinical consequences. Pioneering life-cycle studies in rats demonstrated a "subarachnoid phase" in larval development and migration; recent autopsy findings, outlined here, show it also occurs in humans and has some bearing on treatment. One new and four previously reported cases of human infection are analyzed here, with findings indicating that anthelminthic treatment is effective only when given early and should not be commenced beyond 3 weeks after exposure to infection. In endemic areas, treatment should start as soon as this infection is suspected, even without a clear history of exposure, given the unacceptable risks of waiting for diagnostic laboratory confirmation.

Intestinal parasites of children and adults in a remote Aboriginal community of the Northern Territory, Australia, 1994-1996.

INTRODUCTION: Parasitic infections can adversely impact health, nutritional status and educational attainment. This study investigated hookworm and other intestinal parasites in an Aboriginal community in Australia from 1994 to 1996. METHODS: Seven surveys for intestinal parasites were conducted by a quantitative formol-ether method on faecal samples. Serological testing was conducted for Strongyloides stercoralis and Toxocara canis IgG by enzyme-linked immunosorbent assays. RESULTS: Of the 314 participants, infections were as follows: Trichuris trichiura (86%); hookworm, predominantly Ancylostoma duodenale (36%); Entamoeba spp. (E. histolytica complex [E. histolytica, E. dispar and E. moskovski], E. coli and E. hartmanni) (25%); S. stercoralis (19%); Rodentolepis nana (16%); and Giardia duodenalis (10%). Serological diagnosis for 29 individuals showed that 28% were positive for S. stercoralis and 21% for T. canis. There was a decrease in the proportion positive for hookworm over the two-year period but not for the other parasite species. The presence of hookworm, T. trichiura and Entamoeba spp. was significantly greater in 5-14 year olds (n = 87) than in 0-4 year olds (n = 41), while the presence of S. stercoralis, R. nana, G. duodenalis and Entamoeba spp. in 5-14 year olds was significantly greater than 15-69 year olds (n = 91). DISCUSSION: Faecal testing indicated a very high prevalence of intestinal parasites, especially in schoolchildren. The decrease in percentage positive for hookworm over the two years was likely due to the albendazole deworming programme, and recent evidence indicates that the prevalence of hookworm is now low. However there was no sustained decrease in percentage positive for the other parasite species.

Experimental human infection with the dog hookworm, Ancylostoma caninum.

OBJECTIVE: To investigate possible routes for human infection by the dog hookworm (Ancylostoma caninum). DESIGN, SETTING AND PARTICIPANT: Relatively small numbers of infective larvae were administered orally and percutaneously to an informed healthy volunteer (J K L) under medical supervision, at intervals between May 1998 and May 1999. MAIN OUTCOME MEASURES: Symptoms; weekly blood eosinophil counts; faecal microscopy. RESULTS: A marked blood eosinophilia followed a single oral exposure to 100 infective larvae, while faecal examination remained negative. Eosinophil counts then declined gradually, although a rapid, spontaneous rise several months later, at the beginning of spring, possibly indicated reactivation of dormant larvae. Blood eosinophil numbers did not rise significantly after percutaneous infection with 200 larvae. A subsequent, smaller, oral inoculum of 20 larvae provoked an eosinophil response similar to that of the first experiment. CONCLUSIONS: Our findings suggest that, following ingestion, some infective larvae of A. caninum develop directly into adult worms in the human gut (as they do in dogs). While the percutaneous route might be the most common means of human exposure to canine hookworm larvae, leading generally to subclinical infection, oral infection may be more likely to provoke symptomatic eosinophilic enteritis.

Hookworm aspartic protease, Na-APR-2, cleaves human hemoglobin and serum proteins in a host-specific fashion.

Hookworms are voracious blood-feeders. The cloning and functional expression of an aspartic protease, Na-APR-2, from the human hookworm Necator americanus are described here. Na-APR-2 is more similar to a family of nematode-specific, aspartic proteases than it is to cathepsin D or pepsin, and the term "nemepsins" for members of this family of nematode-specific hydrolases is proposed. Na-apr-2 mRNA was detected in blood-feeding, developmental stages only of N. americanus, and the protease was expressed in the intestinal lumen, amphids, and excretory glands. Recombinant Na-APR-2 cleaved human hemoglobin (Hb) and serum proteins almost twice as efficiently as the orthologous substrates from the nonpermissive dog host. Moreover, only 25% of the Na-APR-2 cleavage sites within human Hb were shared with those generated by the related N. americanus cathepsin D, Na-APR-1. Antiserum against Na-APR-2 inhibited migration of 50% of third-stage N. americanus larvae through skin, which suggests that aspartic proteases might be effective vaccines against human hookworm disease.

Cleavage of hemoglobin by hookworm cathepsin D aspartic proteases and its potential contribution to host specificity.

Hookworms routinely reach the gut of nonpermissive hosts but fail to successfully feed, develop, and reproduce. To investigate the effects of host-parasite coevolution on the ability of hookworms to feed in nonpermissive hosts, we cloned and expressed aspartic proteases from canine and human hookworms. We show here that a cathepsin D-like protease from the canine hookworm Ancylosotoma caninum (Ac-APR-1) and the orthologous protease from the human hookworm Necator americanus (Na-APR-1) are expressed in the gut and probably exert their proteolytic activity extracellularly. Both proteases were detected immunologically and enzymatically in somatic extracts of adult worms. The two proteases were expressed in baculovirus, and both cleaved human and dog hemoglobin (Hb) in vitro. Each protease digested Hb from its permissive host between twofold (whole molecule) and sixfold (synthetic peptides) more efficiently than Hb from the nonpermissive host, despite the two proteases' having identical residues lining their active site clefts. Furthermore, both proteases cleaved Hb at numerous distinct sites and showed different substrate preferences. The findings suggest that the paradigm of matching the molecular structure of the food source within a host to the molecular structure of the catabolic proteases of the parasite is an important contributing factor for host-parasite compatibility and host species range.