It has been reported that there are 1,407 pathogens (viruses, bacteria, parasites, protozoa, and fungi) that can infect humans. Of these, 58 percent are zoonotic, meaning they can be transmitted and sourced from non-human animals. Scientists consider 177 of the pathogens as associated with either emerging or re-emerging diseases. Most are not associated with pandemics, however. Influenza and specifically avian influenza are among the potential re-emerging diseases. The primary concerns associated with influenza focus on the virus’ ability of facilitating genetic drift, shift, or re-assortment, and their pathogenicity in multiple species that primarily cause infections in humans, pigs, horses, and birds, but other species are capable of being either infected or carriers. Four different influenza viruses have infected marine mammals (harbor seals and pilot whales). These traits provide potential for intra species transmission and a possibility for the enhancement of virulence due to the frequency of genetic re-assortment within the species.
The influenza viruses affecting humans and animals belong to the family Orthomyxoviridae, derived from Greek orthos meaning proper and myxo meaning mucus. Though the viruses tend to replicate in cell nuclei of the intestinal tract and shed in the feces, clinical signs are most apparent as respiratory diseases. Influenza viruses are typed into A, B, and C. All are autogenically distinct and all three types have been identified in humans. Influenza A virus is the most important member of the above types and is the most pathogenic in animals and humans. Isolates of influenza A virus are further grouped into subtypes on the basis of their H and N antigens. Currently, 15 H antigens and nine N antigens are recognized, though new subtypes of influenza A virus emerge periodically. Most of the subtypes are typically of low pathogenicity. A few, however, cause severe systemic infections with high mortality. Subtypes H5 and H7 are known to possess greater pathogenic properties. The current H5N1 has emerged as a concern and commands the current media attention and hype. The H5N1 subtype emerged as a highly pathogenic avian influenza (HPAI) in 1997 when it was diagnosed in a young child in Hong Kong. The subtype previously had not been identified outside of avian species. This prompted the destruction of 1.5 million birds and resulted in 18 human confirmed diagnoses and six deaths. The risk factor for human infection was contact with infected poultry but not the handling, cooking, or consumption of poultry meat. HPAI has now been diagnosed in a number of countries (estimated at more than 50 nations) in the avian species and some 148 human deaths reported. Nearly 50 percent of humans infected with H5N1 have died. In 2004, HPAI of strain H5N1 infected poultry and wild birds in nine Asian countries. In Thailand and Vietnam, 37 human cases were confirmed, with a case fatality rate of 68 percent. Again, infection was attributed to direct handling of infected live or slaughtered poultry. Recent reports from around the world continue to be reported both in avian species as well as humans. The isolation of H5N1 avian influenza subtypes reported in surveillance data, however, have consisted primarily of the low pathogenic avian influenza virus. It must be emphasized that avian influenza viruses exhibit host adaptation and rarely infect humans, usually as isolated individual cases without resulting in human-to-human transmission.
Is a flu epidemic of pandemic proportions possible? Certainly! There have been five recognized as such: 1890 (H2N8), 1900 (H3N8), 1918 (H1N1), 1957 (H2H2), and 1967 (H3N2). The great human pandemic of 1918 that more realistically killed 20 million to 50 million people worldwide was an influenza virus that originated in swine. It should be noted that all pathogens have the potential to adapt or modify to enhance their pathogenicity, but the genetic shift can also result in a decrease in pathogenicity. Similarly, prevention of and transmission of disease crosses numerous parameters regarding disease control and treatment for both man and animal. The caliber of veterinary and medical infrastructure and today’s technology cannot be likened to those of the past and even to the last pandemic of 40 years ago. Couple these advances with international partnerships that have been established to strengthen the preparedness, surveillance, and response efforts to provide great resolve (i.e., International Partnership on Avian and Pandemic Influenza).
There are over 175 nations that have national plans for combating avian and pandemic influenza. The U.S. Department of Agriculture (USDA), Department of Interior, and Environmental Protection Agency are all currently cooperating with states in surveillance and other protective programs not only for avian influenza but other zoononic diseases. USDA has published an avian influenza response plan that is well articulated. The Illinois Department of Natural Resources and numerous other state agencies are currently monitoring the wild bird and migration species as well as at-risk domestic poultry flocks. The slaughter and meat inspection programs administered by the Animal and Plant Health Inspection Service provides further surveillance measures for both poultry and swine processed at licensed facilities. Therefore, numerous measures, plans, and preventative practices have been initiated and are in place specially addressing influenza diseases and now concentrating on HPAI.
Without doubt, there is reason to be concerned regarding the potential for avian influenza as with all potential zoonotic and emerging diseases. The concern must be focused to the rational and scientific preparation of addressing prevention and control programs that include their description in terms of bumper sticker messages without hysteria, fear, and dramatization of potential health risks to the global population.
Prevention and control of influenza does not differ from that required for other diseases. A definitive diagnosis for the initiation of well-planned and coordinated response programs for treatment, containment, and eradication are paramount. Whether the concern is foot and mouth disease, swine fever (cholera), bovine spongiform encephalopathy, or avian influenza, proper examination and diagnosis becomes the first line of defense in any disease outbreak or the initiation of a pandemic. Proper decisions for treatment, or in the case of a highly contagious disease in animals the detection, control, and eradication, must be made as quickly as possible.
Are We Prepared?
The answer to this question is extremely difficult to answer. As a veterinarian, I have greater confidence in the preparation regarding avian influenza when compared to several other emerging diseases. However, the critical challenge with influenza is the inherent changing properties of the RNA viruses. This complicates the preparation of vaccines as preventative tools. Even the human flu vaccines change annually in their strain components based on current surveillance data. Vaccines that contain live or modified live components provide greater immune response but are globally discouraged and even prohibited due to the potential for the replication and initiation of disease. Vaccines and vaccination programs are encouraged to be used under strict medical advice. Humans are encouraged to acquire annual flu vaccinations, especially if they are in close contact with animals. The research currently devoted to vaccine development and pharmaceutical preventatives for both human and animals is very encouraging. It is also rewarding to note the personal protection and safety procedures adopted by many producer groups, slaughter and processing facilities, veterinarians, physicians, and first response and surveillance personnel. The rendering industry is encouraged to do likewise. Procedures need to be company and facility specific.
Even referencing the previous plans and preventions, there are, however, a number of not so encouraging observations. In order to control specific and major diseases in the animal sector, the means to identify and document animal movement is a necessity. The current proposed National Animal Identification System (NAIS) has been discussed for the past 15 years. Though it may appear closer to adoption and implementation, it certainly remains controversial and emotional. To the extremes, a friend and colleague, Dr. Don Hoenig, state veterinarian of Maine, experienced the confrontation of two masked individuals that burst into a meeting he was discussing to answer questions regarding NAIS, screaming “No animal ID” and hurled aluminum pie plates containing horse manure at him. This really isn’t the kind of bumper stickers American animal agriculture needs.
Contrary to statements from certain industry segments, housed animals are at reduced disease risk when compared to those reared free range. This is particularly true with poultry and their exposure to wild bird vectors, and swine’s exposure to wild birds and feral swine. Fortunately, the majority of U.S. animal production is raised under secure systems. It is estimated that over 95 percent of the chickens produced in the United States are raised under regulatory secure conditions and slaughtered under regulatory surveillance. Both provide management and regulatory oversight conducive to animal health and food safety. But the trend toward free range and on-premise slaughter is increasing.
The feed and rendering industries have also contributed greatly to animal health and food safety. Both have most recently re-incorporated third party audits and certification programs into their production procedures. The Safe Feed/Safe Food (SF/SF) Certification Program of the American Feed Industry Association has resulted in over 450 facilities committed to certification as action to promote feed safety and enhance the confidence in the U.S. food supply. The Animal Protein Producers Industry has similarly developed and promoted a code of practice (COP) for the certification of rendering facilities. Twenty facilities have received certification with 40 facilities budgeted to be audited during the next year. Participation in both SF/SF and COP needs enhanced commitment. Programs such as these need to be highly prioritized and encouraged throughout the animal food production processing and distribution chain. As important as getting it done is telling the end consumer what is being done in laymen’s terminology that can fit on a bumper sticker.
Summary
The influenza virus has plagued humanity for centuries. Flu-like syndromes have been described in documents dating to 412 BC. Much has been learned about this evolving organism. Predictions for today’s risk factors cannot be the forecast based on yesterday’s results. Nor can we understate the potential that influenza viruses possess for disease causation.
At the same time, the U.S. population should be assured that risk is not equal in all parts of the world. Countries with a much greater proportion of their population in very close proximity to poultry and swine, which may include home slaughtering, are at a completely different risk level. We should review, expand, and communicate the controls in place to reduce the anxiety without complacency.
Dr. Pearl and Veterinary Associates P/S are located in Bloomington, IL. He is past president and director of technical services of the Fats and Proteins Research Foundation and is an adjunct professor, Clemson University.
Tech Topics - December 2006 Render