Avian Influenza, also called avian flu, is an infectious disease caused by an Influenza A virus, which generally affects all types of birds and sometimes mammals. It is of global importance today because of the effects it can have at a sanitary and productive level.

What exactly is avian influenza?

Avian Influenza is a type of virus whose genetic material is made up of a single, negative chain of RNA. It is caused exactly by Influenzavirus A, which belongs to the Orthomyxovirus family. For its classification, two proteins that the virus has on the surface are taken into account: Hemagglutinin (H) and Neuraminidase (N); There are 16 different H antigens and 9 different N antigens. An example of avian influenza of global importance is that caused by Influenza A is H5N1.

How is its transmission?

Avian flu is widely distributed worldwide. According to the OIE (World Organization for Animal Health), until 2016 it had been detected in 77 countries. On the other hand, it is known that this viral disease can affect birds such as chickens, quail, pheasants, turkeys, and other domestic birds. In these birds, the virus spreads rapidly by direct contact with fecal matter, nasal and eye secretions from infected birds. Also, the virus can be spread through contaminated materials such as shoes, clothing, equipment, vehicles, drinking fountains, or feeders.The mobilization of live birds facilitates the transmission. All the above makes Influenza A highly contagious among birds.

In addition to this, wild birds are considered reservoirs of the virus (that is, they carry and transmit it, but they do not get sick). This is important because the participation of migratory aquatic birds (such as ducks or seagulls) in the mobilization of the virus from one country to another has been demonstrated. However, the strains isolated from these birds are of low pathogenicity.

It should be noted that there is no evidence to indicate the transmission of this virus through the consumption of poultry meat or cooked eggs. Humans who can eventually be infected are those who work closely with infected birds.

What symptoms do we see in birds?

To understand the possible signs that this disease generates in birds, we must know that the strains are classified into two categories: 1) Avian influenza of low pathogenicity and 2) Avian influenza of high pathogenicity

In low pathogenic strains, the following can be observed:

• Messy and broken feathers
• Slight depression
• Mild respiratory symptoms such as sneezing
• Decreased animal production: low egg-laying or less weight gain in broilers

High pathogenic strains generate signs such as:

• Prostrated and depressed birds
• Severe decrease in egg production or daily weight gain
• Eggs with soft shells or without shell
• Presentation of edema (fluid accumulation) on the ridge, near the eyes and caruncles
• Ocular and nasal secretions, with coughing and sneezing
• Abnormal postures and incoordination in movements
• In cases of sudden death, the signs are not evident; some birds may die suddenly and in the next 48 hours reach 100% mortality

Why is it so important worldwide?

Avian Influenza or avian flu has a significant component both at a sanitary and productive level due to its behavior and the species of animals it affects worldwide. Regarding its role in public health, the three major pandemics described that have been caused by Influenza A in the last century must be highlighted: in 1918 by H1N1, in 1957 by H2N2 and in 1968 by H3N2. Currently, surveillance agencies worldwide remain alert to the possibility of an outbreak of Influenza A that can be transmitted to humans or pig populations. Some strains of avian origin isolated in humans since 1997 that have caused some deaths, involve H5N1, H7N7 and H9N2.

Its implications at a productive level are far-reaching. If a highly pathogenic virus, characterized by its rapid spread and high mortality, is detected as the cause of an outbreak, commercial restrictions, massive slaughter of the birds involved and quarantine of the surrounding areas will take place. An example of this was a 2015 outbreak in the United States, listed as the most devastating infectious animal outbreak in the history of that country due to the death of 48 million production birds.

How is the disease diagnosed the avian influenza?

In addition to the clinical signs observed in birds, the corresponding entities in each country can take samples of the birds for diagnostic tests. These tests can range from the identification of the viral agent thanks to viral isolation or the RT-PCR test (Polymerase Chain Reaction with Reverse Transcription), to serological tests such as Hemagglutination Inhibition (HI) or ELISA. Each country follows the guidelines of the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.

Its differential diagnoses are acute avian cholera, pathogenic Newcastle Disease and Acute Infectious Laryngo-tracheitis.

What are the control measures for this disease?

Avian influenza has no treatment. Regarding vaccination as a prevention method, each country must take into account the behavior of the disease in its region to decide whether to apply it or not. Therefore, control measures are also based on prevention. Some of those measures related to the productive farm are:

• Farm infrastructure equipped with small hole meshes to prevent wild birds from approaching and entering the production
• Correct disinfection of equipment, vehicles and utensils that enter the farm: iodine compounds, formalin and lipid solvents are useful
• Restricted access to external people
• Prevent the entry of birds whose sanitary status is unknown
• Hygienic handling of food and proper disposal of fecal matter, carcasses and other animal products

If an outbreak occurs, the recommendations to follow are:

• Slaughter of the avian population involved under bioethical standards
• Report to the health authority of each country, which in turn will report the case to the OIE
• Quarantine of the area and a minimum period of 21 days before reintroducing animals to the same farm

Finally, Avian Influenza or avian flu is one of the most important infectious diseases of viral origin in veterinary medicine, in human medicine and in the production systems of the world. The different international animal health organizations, production companies and commercial farms have joined forces in the control and management of this disease, the effects of which can be devastating. Hence the importance of understanding how it behaves and how it is prevented.

REFERENCES:

• Morin, C. W., Stoner-Duncan, B., Winker, K., Scotch, M., Hess, J. J., Meschke, J. S., & Rabinowitz, P. M. (2018). Avian influenza virus ecology and evolution through a climatic lens. Environment international, 119, 241-249.
• Li, H., & Cao, B. (2017). Pandemic and avian influenza A viruses in humans: epidemiology, virology, clinical characteristics, and treatment strategy. Clinics in chest medicine, 38(1), 59-70.
• (2018). Manual de las pruebas de diagnóstico y de las vacunas para los animales terrestres. Capítulo 3: Enfermedades de la Lista de la OIE y otras enfermedades importantes. 8va edición.
• (2017). Influenza aviar en las aves. Disponible online en: https://espanol.cdc.gov/flu/avianflu/avian-in-birds.htm
• Quinn, P. J., & Markety, B. K. (2005). Elementos de microbiología veterinaria (No. 636.09 Q443e Ej. 1). Editorial Acribia.
• Imágenes obtenidas de Pixabay.com (Licencia Pixabay: Gratis para usos comerciales. No es necesario reconocimiento)