Influenza

Test codes:
S0077 - Ultrasensitive qualitative detection of influenza virus by reverse transcription real time polymerase chain reaction
P0013 - Equine respiratory panel (includes influenza and other pathogens)

Influenza is one of the most important respiratory diseases of the horse. It is a severe acute upper respiratory infection, and typical symptoms include pyrexia, dyspnea, anorexia and coughing. In countries where breeding and racing horses is a major industry, outbreaks of the disease can result in significant economic loss.

The virus causing equine influenza belongs to the orthomyxovirus family. There are two subtypes of equine influenza virus, A/Equi 1/H7N7, first isolated in 1956, and A/Equi 2/H3N8, first isolated in 1963. Both subtypes have caused disease. However, it is generally accepted that A/Equi 1/H7N7 has not been isolated since 1979 and may be extinct (van Maanen and Cullinane, 2002; Webster, 1993). In contrast, outbreaks of A/Equi 2/H3N8 continue to occur worldwide with the exception of a few isolated areas where equine influenza has never been recorded, including Australia, New Zealand and Iceland.

Infection with subtype A/Equi 2/H3N8 is enzootic in North America and Europe. Evidence suggests that two separate lineages of this subtype have evolved, and outbreaks occur frequently despite mandatory vaccination of some horse populations (Daly et al., 1996; Mumford and Wood, 1993; Office International des Epizooties, 2000). Influenza is a highly contagious disease and the introduction of even a single infected horse can lead to its rapid spread in unprotected horses over a wide geographic area. In South Africa in 1986, the introduction of the virus into the country for the first time resulted in thousands of horses suffering severe respiratory disease and horse racing was suspended for 5 months.

The increase in international movement of horses by air transport for racing and breeding purposes has led to the requirement for a rapid method to isolate horses that are carriers of this virus. Traditionally, equine influenza virus is diagnosed by the isolation of virus from nasopharyngeal swabs in embryonated hen eggs, or by the detection of a fourfold-or-greater rise in antibody titer in paired sera by hemagglutination inhibition (Office International des Epizooties, 2000). A recent study (Quinlivan et al., 2004) has shown that both virus isolation and molecular detection by reverse transcription PCR are much more sensitive than serological methods such as the Directigen Flu A test. In contrast to virus isolation, reverse transcription PCR detection is rapid and highly specific.

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of influenza virus
• Ensure that horse populations are free of influenza
• Early prevention of spread of this virus
• Minimize personnel exposure to this virus
• Safety monitoring of biological products that derive from horses

References:
Daly, J. M., Lai, A.C.K., Binns, M.M., Chambers, T.M., Barrandeguy, M. and Mumford, J.A. (1996) Antigenic and genetic evolution of equine H3N8 influenza A viruses. J. Gen. Virol. 77:661-671.
Mumford, J. A., and Wood, J.M. (1993) WHO/OIE meeting: consultation on newly emerging strains of equine influenza. Vaccine 11:1172-1175.
Office International des Epizooties (OIE) (2000) Equine influenza, p. 546-557. In Manual of standards for diagnostic tests and vaccines. OIE, Paris, France.
Quinlivan, M., Cullinane, A., Nelly, M., Van Maanen, K., Heldens, J. and Arkins, S. (2004) Comparison of sensitivities of virus isolation, antigen detection, and nucleic acid amplification for detection of equine influenza virus. J. Clin. Microbiol. 42:759-763.
van Maanen, C. and Cullinane, A. (2002) Equine influenza virus infections: an update. Vet. Q. 24:79-94.
Webster, R. G. (1993) Are equine 1 influenza viruses still present in horses? Equine Vet. J. 25:537-538.

Specimen requirements: Preferred sample: nasopharyngeal swab, shipped overnight at room temperature.

Less preferred sample: 1 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, shipped overnight at room temperature.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative reverse transcription real time PCR

Normal range: Nondetected