Geographical distribution and incidence of Angiostrongylus lungworms (Nematoda: Angiostrongylidae) and their rodent hosts in Thailand.

The rat lungworm Angiostrongylus cantonensis, a zoonotic parasite, is known to be responsible for eosinophilic meningitis and meningoencephalitis in humans in many countries worldwide. Another congener A. malaysiensis is a potential pathogen. Rodents as natural definitive host of the parasites are abundant and globally widespread. In this study, the prevalence of Angiostrongylus infection in wild rats was investigated in twenty-four provinces of Thailand during the period December 2011 to June 2014. Of the 669 wild rats sampled, 46 (6.88%) were infected with Angiostrongylus lungworms. The rodents harbouring A. cantonensis worms included Bandicota indica, Bandicota savilei, Rattus exulans, Rattus norvegicus, Rattus rattus complex and Rattus tiomanicus, and those harbouring A. malaysiensis were B. savilei, Rattus losea, R. norvegicus and R. rattus complex. No parasite was recovered from Maxomys surifer (n=11), Mus musculus (n=1), Niviventer fulvescens (n=2), Rattus argentiventer (n=4), Rattus nitidus (n=3) and Sundamys muelleri (n=3). In positive rats, the incidence of infection with Angiostrongylus lungworms was variable among host species and provinces. There were also considerable variation in the proportion of male and female worms among rodent hosts and localities. Two hundred and thirty-five of the collected worms were male and 282 were female. The mean worm burden in the positive rats was 11.24 and ranged from 1 to 61. 81.82% (423/517) of the adult worms were morphologically identified as A. cantonensis, and 18.18% (94/517) were A malaysiensis. One R. rattus from Prachuap Khiri Khan had mixed infection of A. cantonensis and A. malaysiensis (10 worms of each species). The overall number of male (202) and female (221) A. cantonensis worms was not significantly different (χ2 = 0.86, 0.50 > P > 0.30). However, the overall number of male (33) and female (61) A. malaysiensis worms was significantly different (χ2 = 8.34, P < 0.01). The present study added one new definitive host (R. tiomanicus) for A. cantonensis and two new definitive hosts (B. savilei and R. losea) for A. malaysiensis in Thailand. Our data update and contribute significantly to existing knowledge of the geographical distribution of A. cantonensis in wild rats in Thailand and confirm the occurrence of A. malaysiensis throughout the country.