Down with the flu? While some folks are wishing they had gotten around to getting a flu shot, others who did may still have their ears perked as international headlines shout, "Bird flu kills humans."
Most people have never heard of "bird flu," so questions abound: What is it? Can it be controlled? What are the consequences of outbreaks in poultry? How do outbreaks spread within a country? Is there evidence of human-to-human transmission? Are drugs available for prevention and treatment?
I, too, found my curiosity tweaked, wondering how this particular virus might compare to Newcastle's disease. I'm fairly familiar with Newcastle's and the devastation it wreaks in the wild as well as with domesticated poultry. In the early 1990s the Midwest had a notable outbreak of Newcastle's. The disease was suspected or confirmed in our state as well as in North Dakota, South Dakota, Nebraska, Canada and on islands in Lakes Michigan and Huron.
Pelicans and cormorants in the wild were afflicted. At least 771 young cormorants died in the outbreak at Lye Lake near Fergus Falls and several thousand pelicans and cormorants were incinerated at Lac Qui Parle Wildlife Management Area in southwestern Minnesota in an effort to halt the deadly spread.
While I can't recall to what extent poultry farms in Minnesota were affected by Newcastle's, a turkey flock near Devils Lake, N.D. was struck by the highly contagious disease and it was recommended the entire flock of 27,000 birds be destroyed.
Now back to avian influenza, which is more commonly called bird flu. It's also referred to as the H5N1 virus. Since there are so many aspects and angles, I'll limit this column to a few particulars about bird flu as it relates to birds.
The information I present, some it verbatim, comes from the World Health Organization (WHO), U.S. Center for Disease Control (CDC) and the United Nations Food and Agricultural Organization (FAO).
Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first identified in Italy more than 100 years ago, occurs worldwide. All birds are thought to be susceptible to infection with avian influenza, though some species are more resistant to infection than others. Infection causes a wide spectrum of symptoms in birds, ranging from mild illness to a highly contagious and rapidly fatal disease resulting in severe epidemics.
The latter is known as "highly pathogenic avian influenza." This form is characterized by sudden onset, severe illness and rapid death. Mortality can approach 100 percent.
Fifteen subtypes of influenza virus are known to infect birds, thus providing an extensive reservoir of flu viruses potentially circulating in bird populations. To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses of subtypes H5 and H7.
Migratory waterfowl, most notably wild ducks, are the natural reservoir of avian influenza viruses, and these birds are also the most resistant to infection. Domestic poultry, including chickens and turkeys, are particularly susceptible to epidemics of rapidly fatal flu.
Direct or indirect contact of domestic farm flocks with wild migratory waterfowl has been implicated as a frequent cause of epidemics. Live bird markets, such as those found in Asia, have also played an important role in the spread of epidemics.
In my opinion, in many poultry operations the cramped and confined quarters of domestic birds are a major contributor to the spread of such diseases. Any animal population, humans included, if crowded together are significantly more susceptible to contracting and passing pathogens. In addition, the stress factor in caged animals is exceedingly high, which in turn reduces their immunity and ability to fend off afflictions.
Certain water birds act as flu hosts by carrying the virus in their intestines and shedding it. Infected birds shed virus in saliva, nasal secretions and feces. Avian flu viruses spread among susceptible birds when they have contact with contaminated nasal, respiratory and fecal material from infected birds. Fecal-to-oral transmission is the most common mode of spread.
Most flu viruses cause no symptoms, or only mild ones in wild birds. However, the range of symptoms in birds varies greatly depending on the strain of virus and the type of bird. Infection with certain A viruses (for example, some H5 and H7 strains) can cause widespread disease and death among some species of wild and especially domesticated birds such as chickens and turkeys.
Recent research has shown that viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses. During a 1983-84 epidemic in the United States, the H5N2 virus initially caused low mortality, but within six months became highly pathogenic, with a mortality approaching 90 per cent.
Control of the outbreak required destruction of more than 17 million birds at a cost of nearly US$ 65 million. During a 1999-01 epidemic in Italy, the H7N1 virus, initially of low pathogenicity, mutated within 9 months to a highly pathogenic form. More than 13 million birds died or were destroyed.
The quarantining of infected farms and destruction of infected or potentially exposed flocks are standard control measures aimed at preventing spread to other farms and eventual establishment of the virus in a country's poultry population.
Apart from being highly contagious, avian flu viruses are readily transmitted from farm to farm by mechanical means, such as by contaminated equipment, vehicles, feed, cages or clothing. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. Stringent sanitary measures on farms can, however, confer some degree of protection.
In the absence of prompt control measures backed by good surveillance, epidemics can last for years. For example, an epidemic of H5N2 avian influenza, which began in Mexico in 1992, started with low pathogenicity, evolved to the highly fatal form, and was not controlled until 1995.
Those are the nuts and bolts about bird flu in avians. There is a great deal more that could be said, but it gives you the overall picture.
In a future column, I'll address the transmission of the virus to humans and the global perspective as the disease spreads from country to country. Like West Nile and Newcastle's disease, I believe the long arm of avian influenza will reach into Minnesota. In fact, I'm confident new preventative protocols are being written on the national and state level.
Brainerd Dispatch ©2013. All Rights Reserved.