South African Researchers Probe Herpes Virus as Potential Cause of Mass Sardine Die-Off

JOHANNESBURG — Researchers in South Africa are investigating whether a herpes virus is driving the mass mortality of sardines washing up along the country’s western and southern coasts. While the Department of Forestry, Fisheries and the Environment has yet to reach a definitive conclusion, scientists have confirmed that pilchard herpesvirus (PHV) has been identified in local sardine populations for the first time.

PHV was previously linked to two significant sardine mortality events in Australia during the 1990s. According to the South African environment department, the virus can cause the gills of sardines to inflame and thicken, which significantly hinders their ability to absorb oxygen.

It is important to note that sardines and pilchards are essentially the same species, with sardines representing the smaller, younger individuals. The department emphasized that PHV is a fish-specific virus that poses no threat to human health, and its presence does not affect the safety of commercial catches or canned sardine products.

Scientists from the South African Institute for Aquatic Biodiversity and a local university are currently examining dozens of specimens, both live and dead, collected from the affected regions. Initial findings indicate that dead fish from the mortality sites show consistently high levels of PHV, whereas live fish exhibit varying levels of the virus.

While investigators have evaluated other potential causes—such as harmful algal blooms, unusually low sea temperatures, or oxygen depletion—the environment department stated that “the evidence increasingly points to PHV as the leading explanation.”

Dalene Vosloo, a biological sciences lecturer at the University of KwaZulu-Natal who is not part of the official investigation, suggested that the virus might not be the sole culprit. She noted that “it remains possible that multiple factors contributed to the mortality event,” explaining that shifts in water quality or temperature can often leave fish more susceptible to disease.

The mass die-off has also resulted in industrial complications. The Koeberg Nuclear Power Station, located north of Cape Town and serving as Africa’s only nuclear facility, was forced to reduce power output by 50% at one of its two units after dead sardines clogged a seawater intake, according to the national electricity provider.

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