Occurrence of Cryptosporidium oocysts in commercial oysters in southern Thailand

Abstract

The enteric parasite Cryptosporidium is spread through the fecal-oral pathway, most commonly by the consumption of contaminated water but also through food. Because eating raw or barely cooked shellfish might put consumers at risk for cryptosporidiosis, identifying the parasite in oysters is important for public health. A total of 240 oysters, collected from two shellfish aquaculture sites in Thailand's Gulf coast, Nakhon Si Thammarat and Surat Thani, were tested for the presence of Cryptosporidium. Escherichia coli, enterococci, and thermotolerant coliform total levels were measured to assess seawater quality in the shellfish production regions. Oocysts of Cryptosporidium spp. were detected in 13.8% of the samples processed by immunofluorescence analyses. The detection of Cryptosporidium spp. oocysts in oysters obtained from Surat Thani (17.5%) was higher than in those obtained from Nakhon Si Thammarat (9.2%). The difference in detection of positive samples obtained from Nakhon Si Thammarat and those obtained from Surat Thani may be attributed to the effects of physical, ecological, and anthropogenic conditions, resulting in an increased level of marine water contamination by Cryptosporidium spp. oocysts. These findings demonstrate that native commercial oysters obtained from Thailand's southern Gulf coast contained Cryptosporidium spp. oocysts which might serve as a source of human infection. Consequently, these findings pose a serious public health concern and suggest that more quality control measures need to be implemented by the oyster aquaculture business to ensure the safety of seafood.

Keywords: Coastal gulf; Cryptosporidium; Detection; Oysters; Thailand.

Fig. 1

Map of selected sampling areas along the Gulf coast of southern Thailand. This study set oyster sampling locations near the mouths of major rivers in Surat Thani and Nakhon Si Thammarat. Cities and villages along the river basin produce sewage contamination that flows via the river to the sea, where oysters are cultivated. Map symbols: rivers and canals (blue lines); cities and villages (grey circles); oyster sampling sites (red circles). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)