Avian influenza.

Infectious diseases account for more animal and human deaths worldwide than any disease process. Many of these infectious diseases are well established within the human and animal world, with a long history of disease [1]. Influenza, plague, typhus, and pox viruses have an extensive history of wild animal, domesticated livestock, and human infections. The rise of agriculture and animal domestication, the crowding of human populations, climate changes, and human and wildlife behavior have amplified these diseases into endemic cases and epidemic outbreaks [1]. A number of emerging infectious diseases over the last 20 years have illustrated this complex web of animal and human interaction that has long been established with older diseases. A novel coronavirus emerged from wild horseshoe bats in China to cause severe acute respiratory distress syndrome (SARS), leading to a worldwide outbreak. The interactions of bats with other wildlife and the subsequent human handling and consumption fueled the development of this novel virus [2]. Methicillin resistant Staphylococcus aureus (MRSA) has been an emerging pathogen for the past 20 year in humans, with the recent development of a newer strain with increased virulence [3]. This agent now has impacted companion pets of colonized and infected humans and has been seen in a number of veterinary practice and household outbreaks. Finally, the outbreak of Escherichia coli O157:H7 among spinach pointed to a possible wildlife and domesticated animal reservoir, but no clear source was determined [4]. However, emerging infectious diseases have clearly originated in animal sources, accounting for more than 75% of new diseases [5], [6].

Wildlife is perhaps the largest reservoir of these emerging infections [5], [6]. As these diseases evolve, our contact with wildlife leads to initial introduction. Often, the contact between wildlife, domesticated animal, and human occurs concurrently as in a live animal market or on a farm. These crowded animal populations in domesticated settings, or in some situations crowded human populations, act as amplifiers of disease, eventually spreading within multiple species populations. The recent highly pathogenic avian influenza H5N1 worldwide outbreak in domesticated poultry and humans is the clearest example of this complex web of wildlife, domesticated animal, and human interaction [7]. Thus far, billions of domesticated birds have died and over 309 human cases with 201 deaths have been determined. A host of other mammals have been infected as well. Most worrisome is the genetic changes in HPAI H5N1 that occur with viral amplification in animal and human interactions. We have seen genetic drift leading to strain changes and the development of neuraminidase inhibitor resistance, but thus far the larger changes of reassortment have not occurred [7]. This concern over the development of a novel strain of influenza A has lead to calls for a wildlife health, veterinary, and human health collaboration (i.e. a One Health approach) to study and track the entire ecosystem of the virus. This ecosystem would span surveillance and epidemiology, basic science and immunology, and treatment and public health response within the wildlife, veterinary, and human disciplines.

This special issue of Comparative Immunology, Microbiology, and Infectious Diseases on avian influenza spans the ecosystem approach to this important and emerging disease. Lupiani and colleagues give us a historical context to avian influenza and placing the current HPAI H5N1 outbreak into context with past outbreaks with birds and humans. Lee and Saif provide a scientific and basic approach to the structure and nature of influenza A viruses while Yee and colleagues outline the epidemiology of the recent HPAI H5N1 outbreak. Boyce and colleagues tackle the nature of avian influenza in wild birds, its natural reservoir, and how surveillance and monitoring this ecosystem is particularly difficult. Cardona and colleagues move us into the expanded disease process of avian influenza in all animal species in a detailed and important review. Charlton and colleagues discuss the conventional and newer diagnostics of avian influenza that will become paramount for surveillance and disease diagnosis in multiple species. Swayne leads us into the response to avian influenza with a discussion of vaccines and other therapies in poultry, the traditional amplifier for avian influenza. Finally, Pappaioanou discusses the ultimate endpoint of the complex wildlife, animal, and human interaction within the ecosystem—a potential novel strain of HPAI H5N1 that has sustained transmission in humans as the next pandemic.

This issue provides a backbone for avian influenza for wildlife health, veterinary, and human health specialists. This relationship across these disciplines is paramount to early detection, diagnostics, therapeutics, and response to influenza throughout its ecosystem.