The life cycle of the nematode Angiostrongylus cantonensis involves rats as the definitive host and slugs and snails as intermediate hosts. Humans can become infected upon ingestion of intermediate or paratenic (passive carrier) hosts containing stage L3 A. cantonensis larvae. Here, we report a quantitative PCR (qPCR) assay that provides a reliable, relative measure of parasite load in intermediate hosts. Quantification of the levels of infection of intermediate hosts is critical for determining A. cantonensis intensity on the Island of Hawaii. The identification of high intensity infection ‘hotspots’ will allow for more effective targeted rat and slug control measures. qPCR appears more efficient and sensitive than microscopy and provides a new tool for quantification of larvae from intermediate hosts, and potentially from other sources as well.

The nematode Angiostrongylus cantonensis is a rat lungworm, a zoonotic pathogen which causes a global, emerging infectious disease known as rat lungworm disease (RLWD). RLWD has been reported in 30 countries, and Hawaii is the epicenter for RLWD in the United States. We conducted a study in wild Hawaiian rats (Rattus rattus) to determine the efficacy of a vaccine developed against a related species (A. costaricensis). Twenty-eight wild adult rats were captured from Waiakea Forest Reserve on the Island of Hawaii. Rats were mated and 41 F1 offspring were vaccinated with two doses of PP2A vaccine, a serine/threonine phosphatase 2A recombinant peptide (4 µg vaccine and 4 µg adjuvant/25 g body weight) at >3 mos. of age. Rats were gavaged with 50 L3 stage larvae at four weeks post-vaccination. Rats were euthanized and necropsies conducted at 51-53 days PI. Spleen weight, spleen length, and lung weight were recorded and number of worms in heart and lungs counted. Adult worms were found in all F1 rats. An average of 20.88 worms/rat reached adulthood with an infective dose of 50 L3 stage larvae. We found no significant differences between vaccinated rats (n=21) and unvaccinated rats (n=20) in spleen weight (p=0.963), spleen length (p=0.830), lung weight (p=0.830) or number of worms collected from the heart and lungs (p=0.882), suggesting the vaccine does not provide adequate protective immunity to guard against infection by A. cantonensis in wild Hawaiian rats.