An outbreak of avian flu in U.S. dairy cattle has federal officials in Canada and the U.S. testing milk sold in stores to ensure pasteurization and other food safety measures are working.
Cows sickened with H5N1 in the U.S. produced milk that was abnormally thick and yellowish. The first known outbreak of this form of H5N1 in dairy cattle has since been confirmed in several U.S. states.
Veterinarians also discovered the virus in the lung of a U.S. dairy cow that didn’t show symptoms and originated from an affected herd. The animal did not enter the food supply.
But federal officials in Canada noted last month that spillover into livestock increases opportunity for genetic changes that could result in a virus better able to infect mammals, which includes humans, “especially if the infections are mild or asymptomatic in cattle and go unnoticed with minimal infection precautions.”
After U.S. scientists discovered fragments of the virus in one in five samples of processed milk, officials on both sides of the border introduced surveillance of milk being sold on store shelves to ensure it is free of traces of the virus.
Early research from the U.S. Food and Drug Administration shows pasteurization works to neutralize H5N1.
A decision by the Canadian Food Inspection Agency to bolster testing of the milk supply is the right move as the U.S. deals with an avian flu outbreak in dairy cattle, infectious disease specialists say, because it adds a layer of safety on top of pasteurization of milk sold in stores.
No cases have been reported in Canadian cows. The Canadian Food Inspection Agency says commercially sold milk and milk products remain safe to consume, largely because all milk sold and used in most types of cheese in Canada is pasteurized.
Here are some of the measures taken to keep disease-causing bacteria and viruses like bird flu out of dairy products in Canada.
How does pasteurization protect against germs like avian flu?
Pasteurization is the process of heating a food to kill germs like bacteria, viruses and moulds.
“Apart from sanitation and hand washing, milk pasteurization has been the best and most effective food safety intervention in history,” said Keith Warriner, a professor of food safety at the University of Guelph’s food science department.
Warriner said dairy products are pasteurized at 72 C for 15 seconds. Historically, that temperature and time were used to reduce a heat-resistant bacterial pathogen in milk called Coxiella burnetii, which causes Q fever, a flu-like illness.
Nowadays, it is pathogens like E. coli O157:H7 in dairy products that lead to outbreaks. But Warriner said such outbreaks are less common in Canada than in the U.S., where some states allow raw milk to be sold.
In Australia, a young boy died in 2014 after his parents gave him unpasteurized (raw) milk to drink, believing it would be good for him. The boy developed haemolytic uraemic syndrome, a complication from bacteria like E. coli getting into the bloodstream and kidneys.
Warriner pointed to the Australian case to show why Canada continues to mandate pasteurization.
After milk from several farms is collected and brought to a dairy plant, scientists conduct analytical tests for safety and quality and food processors then skim the cream and pasteurize the products.
In Canada, farmers may drink raw milk from their own cows but aren’t allowed to sell it to others. There have been legal challenges to the mandate.
Is raw milk safe?
In Canada and the U.S., surveys suggest about three per cent of people had consumed raw milk, also known as unpasteurized milk.
Health officials in Canada, the U.S. and other countries say consuming raw milk is not recommended. That’s especially the case in places where avian flu outbreaks have occurred on farms, the World Health Organization said.
Consuming unpasteurized milk is associated with an increased risk of serious illness, particularly for children and populations with reduced immunity, such as those who are pregnant and older adults.
Long-standing recommendations to consume pasteurized or boiled milk and milk products and to wash your hands after handling raw products are meant to protect consumers from a variety of disease-causing microbes, also called pathogens.
Unpasteurized milk contains bacteria such as E. coli, Listeria, Campylobacter and bovine tuberculosis that can lead to very serious health conditions ranging from fever, vomiting and diarrhea to life-threatening kidney failure, miscarriage and death.
Health Canada made pasteurization of milk mandatory in 1991, meaning dairy farmers can’t sell unpasteurized milk. Raw milk cheese is available.
It is legal to sell raw milk in many American states and European countries.
What other products include raw milk?
Raw milk cheese typically isn’t filtered and is not pasteurized, Warriner said.
Cheese made from raw or unpasteurized milk include soft and semi-soft varieties like brie, Camembert and blue-veined cheeses. Cheese makers use raw milk because it adds texture and flavour to the products.
In Canada, the “60-day rule” is used to reduce the hazard from raw milk cheese.
Warriner said the 60-day rule was developed in the 1940s based on a doctor’s observation of a typhoid outbreak. The common source was cheese. Those who were sickened recalled having cheese that was aged for less than 60 days, while those who ate older cheese were fine.
Health Canada recommends that children, older adults, and people with a weakened immune system avoid eating cheese made from raw or unpasteurized milk, especially soft and semi-soft types. “Eat hard cheeses such as Colby, Cheddar, Swiss, and Parmesan made from pasteurized milk,” the department’s website suggested, to reduce risk during pregnancy.
What other safety steps are there?
Veterinarian Moez Sanaa, head of standard and scientific advice on food nutrition at the World Health Organization, told reporters this week in a webinar that several good hygiene practices also help protect the milk supply:
The goal is to reduce viruses or other pathogen loads in the raw milk as much as possible, Sanaa said.
“Different barriers can be built from the farm level,” Sanaa said. “You have the temperature, the possible heating, the lactic acid during the fermentation. We need to think of all those barriers.”