Study reveals Brucella problem for raw dairy products in Tunisia


High levels of Brucella contamination have been found in samples of ricotta, cheese and raw milk in Tunisia, posing a serious risk to consumers.

A study investigated the presence of Brucella in 200 samples of raw milk, ricotta and artisanal fresh cheese, collected from four districts of Tunisia. Results are based on detection of Brucella DNA and do not discriminate between live and dead bacteria.

Brucellosis is a significant public health threat to urban and rural populations in endemic countries, particularly the Middle East and North Africa region, as trade in unpasteurized milk and raw dairy products is widespread, according to the study published in the journal Foods.

Samples were purchased from 75 dairy retail outlets from March to November 2019. Forty samples of raw cow’s milk, 102 of artisanal fresh cheese and 58 of ricotta were collected. The fresh cheese and ricotta samples were made from unpasteurized cow’s milk. All products were unpackaged and had no indication that they had been inspected by a Tunisian organization involved in food safety.

High contamination rates
Brucella DNA was found in 150 of 200 samples, Brucella abortus was detected in 47 samples and Brucella melitensis in eight. Almost half of the products tested contained both species, while 21 were neither Brucella abortus nor melitensis.

Scientists have said that milk pooling is the main source of double contamination. Pooling milk on the farm and in collection centers is a routine procedure in Tunisia.

The researchers found that 86.2% of ricotta samples, 69.6% of fresh cheeses and 72.5% of milk samples tested positive. Brucella contamination rates in the different districts were 94% in Tunis, 86% in Bizerte, 74% in Zaghouan and 46% in Béja.

The sampling period extended from the beginning of spring to the end of autumn, as it coincided with an overproduction of milk and an increase in the consumption of dairy products, particularly during the month of Ramadan. Spring and autumn are the lambing seasons in Tunisia and the temperatures are higher. Both human and animal brucellosis are notifiable diseases in the country.

Cross contamination can also play a role in the spread of Brucella. In addition to the pooling of milk, the use of the same milking equipment, containers and utensils without washing and sterilization measures and the vendors using the same knives to cut cheese and ricotta and the same pitcher to measuring milk can increase the likelihood of cross-contamination between different products, according to the study.

The researchers said the findings should draw attention to the urgent need to overhaul the surveillance system and implement control programs to limit and prevent brucellosis infection in ruminant herds.

“Brucellosis infection through the consumption of dairy products is a serious danger of great public health significance. Our study provides evidence for high Brucella DNA contamination rates and the distribution of Brucella species in unpasteurized artisanal dairy products,” the researchers concluded.

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