Type B flu virus: An emerging threat?

Every season, WHO recommends vaccine that consists of virus strains suitable for a particular time period. But so far, Nepal government has never publicly announced the strains circulating in the country

The World Health Organisation (WHO) has recently updated global distribution of types of influenza viruses. It shows that type B influenza virus has taken over type A influenza virus. For the first time, I have gone through a similar observation: a sudden increase in number of patients with type B influenza virus in Nepal this year.

Influenza or flu is defined as a contagious respiratory illness caused by influenza viruses. There are four types of influenza viruses that are classified into types A, B, C and D. The first three types of viruses can infect humans. Among these, type A particularly causes seasonal outbreaks every year and sometimes even pandemic in humans. Type A viruses are further divided into subtypes based on their type structures. Influenza A (H1N1) pdm09 known as “swine flu”, A (H3N2) known as “Hong Kong flu”, A (H5N1) known as “bird flu” and A (H7N9) known as “avian flu” are well known subtypes. Subtypes H1N1pdm09 and H3N2 have also been detected in Nepal in every flu season.

Type B virus is divided into two lineages known as “Victoria” and “Yamagata”. However, no information is publicly available about lineages of type B viruses in Nepal. The main signs and symptoms of a flu infection are sudden onset of fever with chills, bodyaches, cough with chest discomfort, fatigue and weakness. Vomiting and diarrhea are more common in children. These symptoms can be seen one to four days after the virus infection.

In general, symptoms of flu from type A and B viruses are similar. Nonetheless pneumonia, in particular, is found to be more associated with type B flu in children. Some unusual symptoms have also been observed in patients with type B virus this year.

Dozens of patients who have had influenza like illness (later mostly found to have type B flu) showed improvement after treatment, but returned with worse and prolonged cough which was never seen before.

Likewise, some of the patients had developed rashes soon after the symptoms started. Moreover, for the first time patients with influenza B had been admitted to our hospital (Sukraraj Tropical and Infectious Disease Hospital), who were treated uneventfully. It shows that type B flu is becoming more common but with unusual symptoms, and perhaps even more severe than it was previously thought.

It is often predicted that diseases circulating in India will also appear sooner or later in Nepal or vice versa due to cross-border movement of people. But it was interesting to notice this year an increase in number of type B viruses in Nepal, while type A virus was circulating and causing hospitalisations – and even deaths – in neighbouring India.

At present, the reason for this is not clear, but it can be assumed that type B viruses might have been imported from countries other than India due to rise in global international travel. The other reason, which we can only assume at this point of time, may be Nepalis’ more vulnerability to type B virus than type A virus. Only a thorough genetic analysis can help us to arrive at a firm conclusion.

Presently, Centers for Disease Control and Prevention (CDC) of the United States has warned of a second wave of type B flu virus, which is becoming more common in recent days.  However, it is still not clear which one of the two lineages (Victoria or Yamagata) of type B virus will be predominant in the US population.

Vaccination is the best way to prevent outbreaks and morbidity/ mortality from flu related complications. Unfortunately, too little is known about flu vaccine amongst Nepali people or even amongst healthcare workers.

Every season, the WHO recommends the vaccine that consists of virus strains suitable for that time period. So far, the government has never publicly announced about the strains circulating in Nepal. It is necessary for health care providers to recommend right vaccine to those who are at high risk of serious complications.

Children under five, people above 65 years of age, pregnant women, health care workers and people with chronic underlying condition such as asthma, heart disease, kidney disease, liver disease, diabetes mellitus are especially at high risk of developing flu related complications or even deaths. In Nepal, most of the victims of flu related complications or deaths have been found to be people above 65 years of age.

In February 2018, the WHO recommended quadrivalent vaccines for use in the 2018-2019 influenza seasons, which included Michigan strain of flu A (H1N1) pdm09, Singapore strain of flu A (H3N2), Colorado strain of type B (Victoria) flu virus and Phuket strain of another lineage of type B (Yamagata) flu virus. Regrettably, it is not known what kind of virus stains are actually circulating in Nepal. Based on genetic analysis, health care providers, indeed, can only well explain their vaccine recipients.

So far what we know is type B flu virus mutates slowly than type A flu virus. However, type B flu virus has been found clinically severe similar to type A virus this season. This observation raises some critical questions: Is type B becoming a more virulent flu virus? Does any mutation occur in type B virus? Will type B virus become a pandemic flu in the days to come?

Pun is coordinator at Clinical Research Unit of Sukraraj Tropical and Infectious Disease Hospital, Teku