Recently, at least three people were diagnosed with influenza A (H5N1), commonly known as “bird flu”, in the United States. This virus was found to be linked to dairy cattle outbreaks. It is a highly pathogenic avian influenza (HPAI), and its mortality rate is estimated to be higher than 50 percent.

This unusual virus transmission route, i.e., from cattle/unpasteurised raw milk to humans, triggered a grave concern among policymakers and scientists worldwide.

Generally, bird flu is transmitted to humans through close contact with infected live or dead birds. It is somewhat surprising that the data (from 1997 to 2014) released by the World Health Organization (WHO) showed the H5N1 bird flu virus was widely circulated among children. However, the significance of the bird flu virus circulating in children remains unknown, sparking several questions: What is the source of the virus infections in children? Is the virus easily transmitted through senior family members to the children? Why does the H5N1 bird flu infection appear as a mild illness in children, despite its estimated mortality rate of over 50 percent? Do the antibodies generated after the H5N1 bird flu infection provide sufficient protection from future infections? Is H5N1 bird flu still widely circulating among children, particularly in areas experiencing outbreaks mainly in poultry farms?

The first human H5N1 bird flu cases were first reported in Hong Kong in 1997. Symptoms include fever (often higher than 38 degrees Celsius), cough, sore throat, malaise and body ache. The disease can quickly progress to severe pneumonia and neurologic changes. However, the bird flu virus transmitted from cattle or raw milk did not show severe symptoms in humans in the United States. While two confirmed cases showed mild symptoms, such as pink eyes or conjunctivitis, the third presented with a cough without fever and eye discomfort with watery discharge.

The reason behind different symptoms of the same virus in different people is not well understood at the moment. However, human bird flu cases from cattle/raw milk observed in the US underscores the need to revise the clinical case definition of influenza-like illness (ILI), the main criteria for performing laboratory tests to confirm the virus. The current case definition for ILI is fever (higher than 38 degrees Celsius) and cough with onset within the last 10 days, meaning bird flu cases with pink eyes or conjunctivitis may go unnoticed, especially among dairy farmers.

The US Centers for Disease Control and Prevention (CDC) recently advised workers (who work in dairy farms) to use personnel protective equipment, such as masks, gloves, boots and goggles, to minimise the risk of H5N1 bird flu infection. The virus has been found in the raw milk of dairy cows. Hence, it is also advised to consume pasteurised milk to avoid possible bird flu infection.

In Nepal, dairy farm workers do not use PPE. Therefore, they are at risk of getting infected with several organisms, including the H5N1 bird flu virus, although it has not yet been reported in cattle in our country. Nevertheless, the Government of Nepal should pay attention and initiate surveillance to identify possible cattle-human bird flu transmission. We have been experiencing bird flu (H5N1) outbreaks almost every year for over 14 years. A 21-year-old male died of H5N1 bird flu in Nepal in 2019, although the source of infection, in this case, could not be determined.

What is surprising is that based on WHO data (from 1997 through 2014), the H5N1 bird flu virus was seen most frequently in children below 15 years (nearly 45 percent of all confirmed cases), followed by 15-30, 31-50 and over 50 years of age groups respectively. Strikingly, the H5N1 bird flu was even more common among children under five. It shows that the H5N1 virus can readily reach the child population but is less severe and has lower death rates compared to adults. However, studies on the source of the H5N1 bird flu infection in the child population remain scarce.

Safe and effective vaccines against the influenza virus are available in the global market, and people are advised to get vaccinated yearly, especially in the most vulnerable groups such as older people with underlying health problems, children, pregnant women and immunocompromised people. Regrettably, no vaccines for human use against H5N1 bird flu are available.

Experts believe and even predict that H5N1 bird flu may appear as the next pandemic, which may pose unprecedented challenges to the healthcare system as did by multiple waves of Covid-19 not long ago. “Oseltamivir (Tamiflu)” is an antiviral medicine effective against H5N1 bird flu in humans. Patients infected with H5N1 bird flu from cattle/raw milk in the US were also treated with this medicine and recovered uneventfully. In fact, oseltamivir has been used worldwide for the treatment and prophylaxis of seasonal flu. Developing a safe and effective vaccine against H5N1 bird flu is necessary to combat potential “H5N1 pandemic” threats.