How H7N3 avian influenza spread in Mexico
Were migratory birds responsible for the spread of H7N3 avian influenza in Mexico in 2012, or are poor practices on commercial poultry farms to blame?
Establishing the facts and truths regarding Mexico’s avian influenza outbreaks has unleashed a series of bickering among various voices. Most adhere to the official version, but poultry consultant Dr. Armando Mirande does not, and at the annual convention of the Aneca (National Association of Poultry Specialists of Mexico) in April, he questioned whether migratory birds were really responsible for the spread of the H7N3 virus in Mexico.
Theory of avian influenza spreading via migratory waterfowl doubted
North American migratory birds such as ducks can be carriers of avian influenza, but they do not emanate viruses. There are four migration routes for birds from Canada to the Patagonia, but only two are important for Mexico: the Central and Pacific routes. The Pacific route brings birds from Asia and Central brings most of the birds that go to the southern part of the continent.
It has been reported that the low pathogenic virus was isolated from ducks in January 2012. "If this was true, it demonstrates a serious irresponsibility toward the [Mexican] poultry industry, because it was never told, plus it goes against the principles of the OIE," said Mirande.
According to him, if the virus originated in ducks, there is neither molecular nor epidemiological evidence of adaptation to chickens, plus there's nothing published in any peer-reviewed magazine since the first outbreak in 1994. "I've never seen a duck in a farm, but I have seen sparrows, which also migrate,” said Mirande.
According to Dr. Robert Webster of St. Jude Children's Research Hospital in Memphis, Tennessee, all of the H7N3 viruses in North America are unique, have no precursors and, he emphatically said, the outbreak in Mexico did not originate in ducks.
Epidemiological surveillance carried out by USDA's Wildlife Services over five years with more than 250,000 waterfowl sampled showed a prevalence of 2.4 percent for low pathogenic avian influenza in positive birds.
Mirande emphasized the significance of differences in the amount of water surface area in the U.S. compared to Mexico. Minnesota, where there have been recent outbreaks of highly pathogenic H5N2 avian influenza, is known as the "Land of 10,000 Lakes." Seventeen percent of Wisconsin’s surface area is fresh water, while the Mexican state of Jalisco has just 1.7 percent fresh water surface area, including Lake Chapala, which is the country's largest lake. Without this lake, Jalisco has only 0.3 percent fresh water surface area. The theory of migratory waterfowl does not make sense, according to Mirande.
How is avian influenza traveling?
Despite all this, "it has never been mentioned that the virus could have [traveled via] roads" said Mirande. This is how avian influenza virus reached Tepatitlán, he stated, by road, through sick and misdiagnosed heavy breeder hens. Instead of burying them, they were sent to slaughter in San Juan de los Lagos (in the Los Altos region, in Jalisco).
In addition, the virus traveled with the 11 million live chickens from around Mexico that were moved to the greater Mexico City area. It also traveled with live hens that go south to the states of Tabasco and Chiapas, and with the poultry manure that went north for feedlot cattle.
Mirande said that the most serious problems are health practices: Poultry manure is not heat-treated, and mortality pits are inadequately handled, even by major companies.
Differences in the costs of avian influenza outbreaks
Excluding the current highly pathogenic influenza outbreak in the U.S. and Canada, the four U.S. and Canada outbreaks over the last 30 years resulted in nearly $300 million in direct costs, Mirande reported. Meanwhile, in Mexico in 2012, in just a few months the direct costs amounted to $504 million. Mirande added to these numbers the indirect costs of the 8,160 jobs lost and the loss on unused raw materials, bringing the cost of the 2012 outbreak in Mexico to $742.5 million (Table 1).
Next steps for Mexico
Mexico was the first country in which avian influenza H5N2 became endemic; it is now the first country to have two endemic viruses, with the addition of H7N3. "It is possible, but not likely, that the H7N3 virus in Mexico has emerged from migratory waterfowl, but these birds have not spread the virus to the rest of the country" said Mirande. Poor everyday practices in commercial poultry production are to blame for the spread of the avian influenza outbreak to the rest of Mexico.
Mirande recommends further study of waterfowl to prove or disprove for their alleged contact with migratory birds.
All this has turned the dream of Mexico of being a poultry exporter into the nightmare of not being able to provide even domestic needs. Mexico is not alone. In India, Egypt and China there are very similar conditions with two strains of avian influenza and denial of the situation and vaccination. Maybe it's coincidence, but these four countries are at the same latitude.
Table 1. Comparison of direct costs of avian influenza outbreaks in the US and Canada with those of Mexico
|Avian influenza outbreak||Cost of outbreak|
|USA / Canada|
|H5N2 / Pennsylvania / 1983-84||$64 million|
|H7N2 / Virginia / 2002||$56 million|
|H7N3 / British Columbia/ 2004||$76 million|
|H5N2/ California, Minnesota., Wisconsin., Dakotas/ 2015||$96 million|
|H7N3 / Altos de Jalisco / 2012||$504 million|
Source: Mirande, A. Pre-Congress Course, Annual Convention ANECA, Riviera Maya, QR, Mexico, April 2015, with data from the Economic Studies Office of the UNA.
In a matter of months, Mexico had spent more on one avian influenza outbreak that had the U.S. and Canada in the past 30 years.