Late last month, The New York Times ran a headline that read, “’A Dangerous Virus’: Bird Flu Enters a New Phase”.
The article reports that 900 herds of cattle in the United States have become infected with the dreaded bird influenza virus, H5N1. This follows reports that 100 million poultry – mainly chickens and ducks – have been “put down” in the U.S.in recent years due to the disease.
So far, bird flu infections in pigs have been relatively rare, but this jump to mammals on a huge scale in the U.S. has raised alarms, and pigs, which may be next in line, are excellent incubators for avian flu viruses.
African Swine Fever, or ASF, which ravaged Catanduanes in late 2020 and early 2021 and resulted in the loss of more than 60 percent of the swine population, is caused by a DNA virus, which is quite different from RNA viruses like H5N1, or bird flu.
ASF is not an influenza virus, and it belongs to a family of large viruses that mutate and evolve more slowly than RNA viruses such as H5N1 and H1N1, which is swine flu. ASF is not transmissible from pigs to humans and is thus not a human pandemic threat.
While there exists a formal definition for “virus” – too complicated to reproduce here – scientists cannot even agree if it is a form of life.
However, this commonplace “biological entity” – for lack of a better term — plays an important role in the conduct of daily life in the Province, as in swine flu and ASF, not to mention all the other viruses that have come down the pike lately, most notably Covid-19, which killed 7 million people globally.
Scientists disagree on whether or not viruses are a form of life because viruses lack cellular structure, and they cannot reproduce themselves without a host, such as a pig or a bird.
In any event, pigs are superb hosts for viruses, especially human influenza viruses.
Birds, bats, civets and cats also are excellent hosts.
The exact number of viruses is unknown, but the International Committee on Taxonomy of Viruses has classified 11,273 virus species.
However, viruses also exist in plants and microorganisms, so if it were possible to add them all up, there might be as many as 100 million types of virus globally, virologists say.
A normal human being is host to about 1,500 types of virus and 380 trillion virus particles, but usually these viruses needn’t be feared: Most are bacteriophages, meaning that they eat bacteria and thereby manage the human microbiome by limiting the population of bacteria.
Indeed, experiments are now underway to determine if people infected with antibiotic resistant bacteria like those found in pneumonia can be treated with viruses. There has been limited success.
In evolutionary terms, pigs and humans are closely related. They share a common shrew-like ancestor that lived 65-80 million years ago, according to the Australian Academy of Science. Consequently, pigs and humans share about 98 percent of their DNA.
Pigs are so closely related to human beings that some body parts of pigs have been transplanted into human beings – kidneys, skin grafts, heart valves, and even entire hearts. These so-called xenotransplants are still at an experimental stage.
As previously reported in this newspaper, Catanduanes had 16,195 pigs in 2021 around the time of the ASF outbreak. As of 2023, there were 21,451 head, according to the Swine Situation report published by the Philippine Statistics Authority. There are about 778.64 million domestic pigs worldwide.
With regard to the transmission of diseases, due to the genetic similarity of pigs to humans, human beings catch many of the same viruses that pigs do. For example, H1N1 can be passed back and forth between pigs and humans, and it can lead to pneumonia in humans.
The H1N1 pandemic in 2009, which is thought to have originated in pigs in central Mexico, caused 151,000 to 575,400 deaths globally, according to the United States Centers for Disease Control.
The Spanish Flu of 1918 was also an H1N1 virus, and it killed 25-50 million people, although some estimates are much higher.
The main reason the death toll in 2009 was lower than it was in 1918 is that influenza viruses are constantly evolving, and the strain in 2009 was not as virulent as the one early in last century.
Also, by 2009 there had been advances in vaccines and public health awareness.
H1N1 emerged as a recombination of swine, avian and human influenza strains – hence the notion of pigs as ideal mixing vessels for viruses.
Lurking on the horizon is the feared A H5N1 virus, or bird flu.
Globally, there have been 954 reported cases of H5N1 in human beings, resulting in 464 deaths. This represents a mortality rate of 49 percent – compared to only 1 percent for Covid-19.
H5N1 has arrived in the Philippines. It was first reported in domestic birds in 2022, and outbreaks have occurred in Manila, Pampanga, Cagayan Valley, Sultan Kudarat and Leyte, according to news reports.
H5N1 in pigs has been reported in Indonesia and the United States, but there have been no reported cases in the Philippines.
Symptoms of H1N1 in pigs include fever, coughing, nasal discharge, loss of appetite, lethargy and blue discoloration in legs and feet.
To minimize the risk of infection, pig owners should separate pigs from chickens and ducks, keep an eye out for symptoms, and regularly clean pigpens and equipment with disinfectant.
Bryce McIntyre, PhD, resides in San Andres. He holds a doctoral degree from Stanford University, Palo Alto, California, USA.