Long-Term Study of Vibrio parahaemolyticus Prevalence and Distribution in New Zealand Shellfish

Abstract

bThe food-borne pathogen Vibrio parahaemolyticus has been reported as being present in New Zealand (NZ) seawaters, but there have been no reported outbreaks of food-borne infection from commercially grown NZ seafood. Our study determined the current incidence of V. parahaemolyticus in NZ oysters and Greenshell mussels and the prevalence of V. parahaemolyticus tdh and trh strains. Pacific (235) and dredge (21) oyster samples and mussel samples (55) were obtained from commercial shellfish-growing areas between December 2009 and June 2012. Total V. parahaemolyticus numbers and the presence of pathogenic genes tdh and trh were determined using the FDA most-probable-number (MPN) method and confirmed using PCR analysis. In samples from the North Island of NZ, V. parahaemolyticus was detected in 81% of Pacific oysters and 34% of mussel samples, while the numbers of V. parahaemolyticus tdh and trh strains were low, with just 3/215 Pacific oyster samples carrying the tdh gene. V. parahaemolyticus organisms carrying tdh and trh were not detected in South Island samples, and V. parahaemolyticus was detected in just 1/21 dredge oyster and 2/16 mussel samples. Numbers of V. parahaemolyticus organisms increased when seawater temperatures were high, the season when most commercial shellfish-growing areas are not harvested. The numbers of V. parahaemolyticus organisms in samples exceeded 1,000 MPN/g only when the seawater temperatures exceeded 19°C, so this environmental parameter could be used as a trigger warning of potential hazard. There is some evidence that the total V. parahaemolyticus numbers increased compared with those reported from a previous 1981 to 1984 study, but the analytical methods differed significantly. Because of the halophilic nature and marine habitat of Vibrio parahaemolyticus, raw seafood can naturally harbor this microorganism and is the main food source responsible for the gastroenteritis the microorganism causes (1). A recent report released by the U.S. Centers for Disease Control and Prevention estimated that the average annual incidence of Vibrio species infections in the United States increased by 43% from the 2006 to 2008 period to 2012 (2). The incidence rate of V. parahaemolyticus infection in New Zealand (NZ) is calculated to be 1.6/100,000, increasing to 15.3/100,000 in the Pacific Islander population, with most cases linked to imported seafood (3).An international risk assessment of V. parahaemolyticus in raw seafood highlighted the importance of exposure to raw oysters based on the incidence of V. parahaemolyticus harboring the thermostable direct hemolysin (tdh) and tdh-related hemolysin (trh) genes at harvest (4).NZ has two main islands (Fig. 1) that extend from latitudes 34°t o 47°south. This means that there are diverse habitats and significant differences in water temperature along the length of the country, with cooler waters in the south. The first reported NZ isolation of V. parahaemolyticus was from Bay of Islands' shellfish (5). Subsequently, Fletcher (6) conducted a 3-year surve...

Prevalence, characteristics and ecology of Vibrio vulnificus found in New Zealand shellfish

“…) published by Cruz et al . (). Vibrio vulnificus was detected in 13·6% of Pacific oyster samples ( n = 32) harvested from the North Island, and was not detected in any samples from the South Island ( n = 18).…”

“…), although it was not as clear as that in the parallel V. parahaemolyticus study (Cruz et al . ). The frequency of positive samples for V. vulnificus was significantly higher in summer months than in winter months (June–November vs December–May, P < 0·01).…”

“…The V. vulnificus results broadly correlate with the V. parahaemolyticus data previously described (Cruz et al . ), with harvest site B having the highest recorded incidence of both V. parahaemolyticus and V. vulnificus . In contrast, site F had a lower incidence of V. vulnificus than the average observed for V. parahaemolyticus numbers (Cruz et al .…”

“…In a previous report (Cruz et al . ) we described how 311 Pacific oyster ( Crassostrea gigas ), dredge oyster ( Ostrea chilensis ) and Greenshell ™ mussel ( Perna canaliculus ) samples were collected from the two major islands of New Zealand, and analysed for Vibrio parahaemolyticus numbers in relation to environmental parameters. The current work, based on the same set of samples, aimed to evaluate the effect of environmental parameters (temperature and salinity) on V. vulnificus numbers in New Zealand shellfish.…”

Vibrio bacteria in raw oysters: managing risks to human health

“…While vibrios are often particle attached, Lopez-Hernandez et al [42] hypothesized that non-digestible particles led to downshifts in filter-feeding in oysters. In Brazil, V. parahaemolyticus was found to be negatively correlated with salinity, and studies in New Zealand have demonstrated that salinity is unrelated or negatively correlated to V. parahaemolyticus shellfish abundances, depending on the study [43,44].…”