Enteropathogenic vibrios

The only serogroups of pathogenic V. cholerae currently recognized as causing significant cholera outbreaks are O1 (mostly the Inaba and Ogawa serotypes) and O139 (FDA,2012; Codex, 2010). The key determinants of V. cholerae virulence, the cholera toxin and the toxin co-regulated pilus are parts of horizontally acquired Mobile Genetic Elements (Kumar et al.,2020). Non-O1/O139 V. choleraestrains are less pathogenic (EFSA, 2012).

Enteropathogenic vibrios’ virulence are responsible for the gastrointestinal symptoms, including abdominal cramps, nausea, vomiting, fever, and mild to severe watery diarrhea observed during the infection (FDA, 2012). They mainly induce huge losses of ions and water from the epithelium cells of the human intestines.

The gastroenteritis is generally mild or moderate and self-limiting in healthy people. However, in susceptible people (immunocompromised states, diabetes, AIDS, etc.), the infections can be more severe and require hospitalization as possibly leading to septicemia and death.

V. vulnificus and V. parahaemolyticus also can cause wound infections either through wounds resulting from handling fish, crustaceans, or shellfish, or when a pre-existing wound is exposed to contaminated marine or estuarine waters. Beyond inflammation at the wound site, the infection can become systemic, with affected people developing fever, altered mental status, and hypotension. Resulting lesions frequently require surgical debridement or amputation (FDA, 2012).

Ingestion of large numbers (10 ⁶ - 10 ⁹) of Vibrio cells is usually needed to develop an infection. However, even the initial contamination level could be low on a product contaminated through sea water, the risk of infection increases rapidly due to the high growth rate of Vibrio species, especially at inappropriate storage conditions (EFSA, 2012). A correlation exists between probability of infection and warmer months when water temperatures are greater than 15°C (FDA, 2012).

Vibrio is recognized as a primary cause of bacterial gastroenteritis associated with seafood consumption in many areas of the world, including Asia and the US. The number of infections related to these pathogens has increased since 1990 (Codex, 2010; EFSA, 2012). There is a growing body of evidence to suggest that climate change, coupled with epidemiological and demographic factors are increasing the geographical spread as well as incidence of these pathogens from foodborne sources (Hartnell et al., 2019).

The US CDC estimated that around 50,000 foodborne Vibrio infections occur each year in the US and that hospitalization and death rates range from 22.5% / 0.9 % for Vibrio parahaemolyticus (86% foodborne) up to 91.3 % / 34.8 % for V. vulnificus (47% foodborne) (Scallan et al., 2011). Compared to other major foodborne pathogens, the number of Vibrio infections also appears to be steadily increasing, compared to the years 2016–2018. The US Vibrio incidence in 2019 (0.9 cases / 100,000) increased significantly (79%) (CDC, 2020).

V. parahaemolyticus, Vibrio cholerae, and Vibrio vulnificus are common residents of tropical and temperate marine environments. Their distribution is strongly associated with water salinity. V. cholerae occupies freshwater and brackish habitats, mostly introduced through human feces, where V. vulnificus is present in environments with intermediate levels of salinity and V. parahaemolyticus shows preference to more saline environments and may be present in offshore waters (EFSA, 2012). Epidemic V. cholerae is confined to developing countries with warm climates (Codex, 2010).

Vibrios are concentrated in the gut of filter-feeding molluscan shellfish, such as oysters, clams and mussels, where they can multiply (EFSA, 2012).

Typically, Vibrio infections are initiated from exposure to seawater, consumption of raw or undercooked seafood produce (Hartnell et al., 2019) or drinking waters contaminated with V. cholerae (Codex, 2010; FDA, 2012).

Foods associated with Vibrio infections include crayfish, lobster, shrimp, fried mackerel, mussel, tuna, seafood salad, raw oysters, clams, steamed/boiled crabmeat, scallops, squid, sea urchin, and sardines. 

These products include either raw and partially treated seafood (heat treatment, high pressure) or even thoroughly treated seafood products later exposed to cross-contamination through contaminated food production environments.

Improper refrigeration of seafood products contaminated with Vibrio may allow the rapid proliferation of bacterial cells, due to their high growth rates, with a corresponding increased risk of infection. Vibrio can survive for extended periods in chilled and frozen foods (EFSA, 2012, 2021; FDA, 2012).

The food safety concerns associated with enteropathogenic vibrios and seafood have led to the development by scientific or regulatory bodies of specific risk assessments and potential risk management strategies for their control (FDA, 2005, 2019, 2021; Codex, 2010; EFSA, 2012; FAO, 2016).

All this supports either specific regulations concerning seafoods products (21CFR part 123) or the broader requirements of EU and US regulations i) for the prevention of adulteration (EU 178/2002; Federal Food, Drug & Cosmetic Act,1938; FDA-FSMA, 2011) and ii) for the mandatory implementation of HACCP- based control systems and Good Hygiene/Manufacturing practices (FDA 21CFR 1 et al.; EU 852/2004).