Influenza In Perspective

The equine influenza (EI) epidemic in Australia is over: There have been no new cases since Dec. 25, 2007, and the country was declared provisionally free of EI on March 14, 2008. Large-scale surveys, both targeted and random, are under way to assure EI's continued absence.

The official report of the Australian government's EI inquiry, the product of six months of hearings, recently has been made public. It approaches the source of introduction, how the disease "escaped" into the Australian horse population from imported horses during post-arrival quarantine, and how to strengthen biosecurity protocols to prevent another epidemic.

Rapid establishment of strictly enforced federal and state movement (transport) control zones turned the epidemic's progress from outward expansion to infilling, until the "fuel" of EI-susceptible horses was exhausted. Government-supervised vaccination limited severity and spread , but it wasn't the key to eradication.

In the U.S. there was no threat of a large-scale outbreak caused by the same EI strain because it has been here already, unlike in Australia. Several effective, commonly used vaccines are available here and had been recently updated to include a new virus strain similar to the Sydney/07 virus.

A "business as usual" approach to EI in the U.S., however, minimizes the strategic importance of continued surveillance. Change is the modus operandi of EI virus, and--just like human influenza viruses--EI was an exotic disease once. In 1963-1964 the equine/Miami strain, first of the 'A2' subtype (technically, subtype H3N8), swept through the Americas and Europe, affecting hundreds of thousands of horses. This resembled Australia in 2007, except there was no vaccine or possibility of eradication. The current strains are descendants of that equine/Miami/63 virus.

Vaccine efficacy depends on periodic updating in response to the gradual changes in strains, called antigenic drift. Also, there has not been an exotic EI strain since 1963 (with the exception noted below). Therefore, current surveillance of EI by the OIE (the World Organisation for Animal Health) reference laboratories and OIE Expert Surveillance Panel (that includes this author) mainly tracks antigenic drift.

But that same surveillance also has the mission of promptly recognizing any emergence of an exotic EI. The requirements and the tools are the same, and they include obtaining nasal swab samples from horses with acute respiratory disease (only about a hundred of these are submitted annually in the U.S.), testing them for EI (Australia and New Zealand authorities require a particular EI test on all imported horses) and whether it's the A2 subtype or not, and culture for a more detailed characterization and possible vaccine inclusion.

Could an exotic EI appear in the U.S.? Yes! Witness the transmission of deadly subtype H5N1 "bird flu" to humans in Southeast Asia, prompting the culling of millions of poultry to prevent human infection worldwide. In 1989 another bird virus infected thousands of Chinese horses, killing up to 20% in some herds (this strain disappeared from horses after 1990). Both the A1 and A2 subtypes likely originated as bird viruses. The A1 subtype is thought to be extinct in horses, but the same subtype (H7N7) survives in birds and sometimes causes deadly outbreaks in poultry.

Diagnostic laboratories are the "trip wires" of alarm in any infectious disease outbreak. However, our trip wires in the U.S. are in a worse state of preparedness than Australia's in 2007.

Animal disease diagnostic laboratories, along with the OIE labs, are the "trip wires" of alarm in any equine infectious disease outbreak. However, the fact is that our trip wires in the U.S. are in a worse state of preparedness than Australia's in 2007. There is not nearly enough communication up the ladder from the local level (horse owners and practitioners) to state and national levels (diagnostic labs, USDA, and OIE labs), and not enough horizontal communication at the national level, either.

There is no formal structure to support OIE reference lab activities; they depend upon grants, donations, fees for service, or support from their host institutions. In times of economic stress they are perceived as nonessential and are vulnerable to budget cuts. Among the lessons to be learned from the Australian EI outbreak, the U.S. equine industry should note that seemingly minor weaknesses of infrastructure undermined a quarantine system, resulting in estimated costs to the Australian taxpayers of $100 million and to the Australian equine industry of $1 billion.

Our infrastructure is weaker.

About the Author

Thomas M. Chambers, PhD

Thomas M. Chambers, PhD, is Head of the Office International des Epizooties International Reference Laboratory for Equine Influenza at the University of Kentucky's Gluck Equine Research Center.

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