Insights from a Comprehensive Review on Avian Influenza

Dr. Majid Hamid Al-Sayegh / Australia

Report: Insights from a Comprehensive Review on Avian Influenza

Introduction:

Avian influenza (AI), also known as bird flu, is a disease common to humans and animals caused by viruses belonging to the genus Influenza virus in the family Orthomyxoviridae, and poses a major threat to public health and the economy. Avian influenza affects human and animal health and causes significant economic losses. In this review, we review various aspects of avian influenza, including causes, symptoms, diagnosis, treatment, and prevention strategies, with a focus on the potential of the virus to cause a pandemic.

Causes and characteristics of the virus:

Avian influenza is caused by influenza viruses that consist of eight segments of single-stranded RNA. The virus contains surface proteins, hemagglutinin (HA) and neramidase (NA), which determine the virus’s ability to infect, the severity of the disease, and its ability to adapt to different host species. Avian influenza viruses are classified into subtypes based on HA and NA proteins, with (18) HA subtypes and (11) NA subtypes identified.

Epidemiology :

Avian influenza viruses are not restricted to a specific geographic region and have been isolated from poultry, wild birds, and some domestic animals worldwide. Wild bird migration and human activities such as poultry farming and live bird trade contribute to the global spread of the virus. Wild birds, especially waterfowl, play a role in transmitting the virus most of the time without showing symptoms, but some subtypes such as H5 and H7 can cause severe epidemics in domestic poultry.

Pathogenesis:

Avian influenza viruses are divided into two types: highly pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI). HPAI viruses, such as the H5N1 subtype, cause rapid death in poultry, while LPAI viruses cause mild symptoms such as respiratory illness. The severity of the disease depends on the virus and the type of host bird. Highly pathogenic viruses can spread to multiple organs in the body and cause systemic infections and death, while low pathogenic viruses are mostly confined to the respiratory system.

Diagnosis :

It is difficult to diagnose avian influenza based on clinical symptoms alone, as the symptoms of the disease are similar to many other diseases such as Newcastle disease, botulism, and bacterial infections. Accurate diagnosis requires laboratory tests such as real-time polymerase chain reaction (RT-PCR), hemagglutinin inhibition (HAI) test, enzyme-linked immunosorbent assay (ELISA), and virus isolation through injection into poultry embryos.

Clinical symptoms :

Clinical symptoms vary depending on the virus subtype and the host bird species. Common symptoms in birds infected with LPAI include sneezing, coughing, nasal and ocular discharge, and difficulty breathing. HPAI infection results in sudden death, cyanosis, and swelling of the head and neck area. In severe cases, neurological symptoms such as incoordination and paralysis may occur.

Modes of transmission and facilitators :

Avian influenza virus is usually transmitted from infected birds to humans through direct or indirect contact with infected birds or contaminated environments. Wild birds play a major role in the global spread of the virus, with bird migration contributing to the spread of the virus to new areas. Although human infections are rare, they can occur through handling, slaughtering, or preparing infected birds for food.

Public health importance and economic impact :

Avian influenza is a serious threat to public health, with some subtypes, such as H5N1 and H7N9, causing human infections with high mortality rates. The economic impact of avian influenza epidemics is significant, especially in the poultry industry where millions of birds can be killed to control the spread of the disease, resulting in huge financial losses.

Treatment and vaccination :

There is currently no effective treatment for avian influenza virus in poultry, with the disease being managed using supportive care and biosecurity measures, in addition to culling infected birds. In humans, treatment is with antiviral drugs such as oseltamivir and zanamivir, but resistance to these drugs may become an increasing problem.

Control strategies :

Control of avian influenza requires a comprehensive approach that includes biosecurity measures, surveillance, vaccination, and culling of infected birds. Collaboration between countries to enhance research, share data, and strengthen surveillance systems is needed to limit the spread of the disease.

Conclusion:

Avian influenza remains a major threat to public health and the poultry industry. The potential to cause a pandemic, as well as its economic and health impact, underscores the need for continued research, surveillance, and prevention measures. Developing effective vaccines, improving diagnostic tools, and enhancing biosecurity practices are essential to reducing the risks associated with avian influenza pandemics.