On Nov. 18, Hong Kong health authorities reported that a woman was suffering from the highly pathogenic (A)H5N1 subtype avian influenza virus, commonly known as bird flu. Then, on Dec. 9, the Indonesian Ministry of Health announced that a 21-year-old female from Bandung City in West Java was a new human case of H5N1. These human H5N1 cases have prompted public health systems in Asia to step up their pandemic influenza preparedness. Now that winter has arrived in Taiwan, we need to strengthen surveillance of both humans and animals to guard against highly pathogenic bird flu viruses and prevent them from spreading to humans.
Conventional infectious disease surveillance is generally passive in that it depends on doctors notifying health authorities when cases occur. This is a low-cost system, but it depends on doctors being keen enough to notify the authorities. Another problem arises if there is a high proportion of asymptomatic cases for a particular illness — meaning that many people who are infected do not fall ill — and this is true of the influenza virus.
Besides, the notification rate for infectious diseases of the respiratory and digestive tracts tends to be rather low. If we want to be sure about whether one of the many subtypes of influenza virus that can spread quickly among animals can also cross over to human hosts, a passive surveillance system might be too slow and that could lead to unfortunate consequences. This is especially true of emerging novel influenza viruses, which can spread quickly because most people are susceptible, having no antibodies. Novel virus infections can break out all over the place, with high morbidity rates, leading to a heavy death toll.
The best approach is to routinely conduct serological surveillance studies on people belonging to high-risk groups — ie, those exposed to potential carrier animals — to detect early on whether they have antibodies to animal influenza viruses. This contrasts with the past practice of flu-affected Asian countries, which had been to take body temperature tests in areas where there have been incidents of bird flu.
Enhanced virological surveillance is needed for people who have close contact with animals, such as those working in live poultry markets and livestock farming, when they exhibit respiratory tract symptoms and also for travelers and traders who fall ill, and in places where clusters of influenza infections occur, so as to ascertain whether there have been interspecies transmissions from animals to humans.
When interspecies infections do happen, the eight genomic segments of the viruses must be analyzed to investigate their origin and find out how they are related to animal-borne influenza viruses. It is also important to determine what key risk factors there are for humans to acquire such infections in the locality.
For example, surveillance has been implemented in Indonesia, a country badly affected by bird flu. In West Java Province, it was found that 47 percent of chickens in live poultry markets were infected with bird flu viruses, 44 percent of which had the H5N1 subtype. It was also found that unhygienic waste disposal in such markets and poorly managed poultry transport was an important risk factor.
Such conditions have shown again and again how important it is to conduct routine virological and serological surveillance at live poultry markets where people come into close contact with domestic fowl.
Recently, both Japan and South Korea have reported instances of highly pathogenic avian influenza H5N1 viruses. These viruses were identified from wild birds and poultry in Japan and mallard ducks and eagle owls in South Korea.
On Nov. 27, five dead chickens were found on a poultry farm in Yasugi City in Japan’s Chugoku region and two days later it was confirmed that they had been infected with the H5N1 virus. The World Organisation for Animal Health issued an immediate notification report at the beginning of this month and investigations revealed that another 57 chickens had died.
Japanese people concerned with this outbreak have pointed out that it happened at a poultry farm on the coast that had inadequate bird exclusion nets and that the H5N1 virus isolated from the infected chickens was closely related to the avian influenza virus sample obtained from a wild duck in Hokkaido in October, so they suspect that the virus was spread by wild ducks.
However, scientific confirmation of this theory will require further investigation and comparison of the eight genomic segments of the virus obtained in Japan with avian influenza samples isolated in Southeast Asia, Russia and other places.
Bird flu has occurred in 23 cities and provinces of Vietnam so far this year, mostly in waterfowl, which are a reservoir for the virus. Clearly, the bird flu outlook for East Asia this winter is not bright.
In the spring of this year, several incidents of avian influenza occurred in central Taiwan and were officially identified as a low pathogenic strain of the H5N2 subtype virus. At the same time, last year’s pandemic A(H1N1) influenza virus, known as swine flu, remains as transmissible as ever.
Only time and scientific inquiry will tell whether a genetic reassortment will occur between last year’s swine-origin A(H1N1) and avian H5 influenza viruses, which is the scenario most feared by public health experts around the world.
In the meantime, there should be a reinforced twin-track virological and serological surveillance for avian, swine and human influenza viruses. It is worth noting that Philadelphia in the US, as well as Italy and Mexico, have all experienced instances of longer duration of circulating low pathogenic influenza viruses and their subsequently becoming highly pathogenic virus infections.
Another worry stems from the fact that the woman infected with avian influenza in Hong Kong last month had been traveling in southern China. Considering the increasing frequency of direct shipping and flights across the Taiwan Strait, epidemic prevention measures need to be more stringent than ever.
On Dec. 16, British authorities reported that 14 people under age 60 had died of last year and this year’s pandemic influenza H1N1 virus. This is a reminder that in cold weather, the flu virus can be dangerous for people with underlying health problems.
Since few young and middle-aged people in Taiwan have been vaccinated against this novel influenza virus, further measures need to be taken to reduce cluster outbreaks of influenza.
It is regrettable that, just at this crucial time, Taiwan has a severe shortage of chicken embryos, which are needed for virological surveillance of animal influenza. Evidently Taiwan’s pandemic influenza preparedness is in need of strengthening and improvement. Besides, groups that are particularly vulnerable to pandemic influenza — pregnant women, diabetes sufferers, obese people and those with impaired immunity — should be reminded to get vaccinated to reduce deaths from the flu.
King Chwan-Chuen is a professor in the Institute of Epidemiology and Preventive Medicine at National Taiwan University and an adviser to the Taiwan Association for Promoting Public Health.
TRANSLATED BY JULIAN CLEGG
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