Tick-borne encephalitis outbreak linked to raw milk cheese in France

France has identified its first outbreak of tick-borne encephalitis from consumption of raw milk products, with more than 40 people affected.

The infections are linked to eating a brand of raw milk goat cheese in Ain, in the Rhone-Alpes region, between April and May this year, according to Santé publique France.

The cheese producer is GAEC des Chevrettes du Vieux Valey, based at Condamine in Haut-Bugey, Ain. It is thought ticks carrying the virus contaminated a goat, then its milk, then the cheeses, and finally consumers.

A total of 42 cases of lymphocytic meningitis, encephalitis and infectious syndromes have been identified in people living in the commune of Oyonnax, within a radius of 30 kilometres. Two additional people live in Loire-Atlantique and Jura but consumed the implicated raw milk goat’s cheese. Cases occurred between the week of April 13 to 19 and May 18 to 24 with a peak from April 20 to 26.

Virus found in cheese
At the end of May, the diagnosis of tick-borne Encephalitis (TBE) virus, the agent responsible for tick-borne encephalitis, was confirmed for 33 of the 44 cases. The other 11 are under investigation and biological tests are being done to confirm or rule out the diagnosis of tick-borne encephalitis.

Among confirmed cases, the median age is 49 with the youngest patient aged 11 months and the oldest 86 years old. Thirty people were hospitalized or went to hospital and two have been admitted to intensive care.

Forty-one of 43 cases reported having raw milk cheese from the same producer in Ain from mid-April on. Presence of the TBE virus has been identified in a goat cheese from the company. A recall of dairy products from the firm was carried out before this result was known.

The producer has started pasteurizing goat milk before processing. A withdrawal and recall of products on sale at the time of the alert was conducted in late May.

A statement from GAEC des Chevrettes du Vieux Valey said the TBE virus carried by ticks was found on a single batch of cheeses produced on April 20 with checks on more recent products negative but it continues to discard product from milking until authorities say it can restart sales.

“We are awaiting the results of the blood tests on our goats to ensure that our animals are no longer carriers of this virus. We also wish a speedy recovery to the victims of this virus and we will inform you of the progress of the investigation concerning us,” according to a statement from the farm owners.

Rare infections from food source
Occurrence of sporadic cases of tick-borne encephalitis is not new in the Auvergne-Rhône-Alpes region with a few identified each year. One case was identified at the end of May 2020 in Ain in a person bitten several times by ticks but who did not consume the cheese.

Most infections with the virus result from infected ticks, which often remain attached to the skin for days. On rare occasions, infection can result from consumption of unpasteurized milk from infected goats, sheep or cows, according to the World Health Organization (WHO).

The incubation period of TBE is usually between 7 and 14 days. In an early phase, symptoms may include fever, malaise, anorexia, muscle aches, headache, nausea, and/or vomiting. After an asymptomatic interval, a second phase of disease occurs in some patients who could experience symptoms of meningitis such as fever, headache, and a stiff neck and encephalitis (e.g., drowsiness, confusion, sensory disturbances, and/or motor abnormalities such as paralysis). Encephalitis developing during this second phase may result in paralysis, permanent health issues or death.

Severity of illness increases with age of the patient and there is no specific treatment for tick-borne encephalitis, according to the WHO.

The French Agency for Food, Environmental and Occupational Health and Safety (ANSES) is doing additional environmental studies on ticks and the TBE virus in the geographic area concerned. Investigations are also being carried out, particularly among dairy farmers, because ticks carrying this virus may be present in other municipalities.

(To sign up for a free subscription to Food Safety News, click here.)