Migratory birds can carry many pathogens, including viruses of importance in poultry farming.

Migratory birds: How do they behave?

Many species of birds in the world carry out short- and long-distance migration processes. Migration is a natural phenomenon in which birds travel certain distances depending on the season or climate.

In migratory processes, birds can move within the same country or region, or even from one continent to another. Due to the appearance of the seasons according to the time of the year, birds move between the northern and southern hemispheres.

Migratory birds can be natural reservoirs or hosts for various types of viruses. This means that when they migrate, they are moved from one geographical area to another, and the viruses can infect other poultry. For this reason, in poultry farming, there is great interest in the study and prevention of viruses moved by migratory birds.

Viruses that affect migratory birds can also affect the production of poultry and vice versa.

The main migratory routes

At the continental level, there are eight main routes along which birds migrate (Figure 1):

• Mississippi Route
• Atlantic Route
• Pacific Route
• East Atlantic Route
• Black Sea and Mediterranean Route
• Central Asian Route
• East Africa and West Asia Route
• East Asian and Australian Route

Two migratory periods occur each year: spring and autumn. In autumn (September to November) the birds travel from the northern hemisphere to the continents of the southern part. Some of them stop where they find food and rest, and others keep on traveling to the south. Then, after six to eight months of living in the tropical zones, they return to the northern zone during the spring (March to May).

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Avian viruses and their relation to migration

Viruses are pathogens that have an impact on poultry worldwide, both in wild and in production birds. Therefore, there are some reasons to investigate and learn more about these viruses in migratory birds:

• To study the genetic and molecular evolution of viruses for the development of vaccines.
• To know the epidemiology of these viruses in each region and to take preventive measures.
• Viruses generate a high economic impact in poultry farming by increasing farm mortality, costs of treatment and diagnosis, slaughter of sick poultry, and decrease in production.
• Monitor the transmission of infectious agents between wild and domestic poultry.
• May provide clues to disease resistance mechanisms in those poultry species that do not develop the viral disease.
• Viral diseases in poultry can create tariff and trade barriers that affect a country’s entire industry.

The role of migratory birds

Viruses are currently one of the most important groups of pathogens in poultry farming worldwide. The structure of viruses is relatively simple compared to other infectious agents. However, they cause disease patterns severe enough to cause losses in poultry farming.

There are several viruses of great importance in veterinary medicine that infect both production and migratory birds. Therefore, it is important to study the epidemiology and biological cycles of these viral pathogens to understand how they interact with each group of poultry.

On the other hand, it is recognized that wild birds constantly interact with poultry in low and medium-scale systems. This interaction can facilitate the mobilization and exchange of pathogens in this poultry. This situation is aggravated when the poultry is migratory and carries with them pathogens that are unknown or absent in each region.

Production poultry develops immunity to viruses through active immunity, either natural (by exposure to the pathogen) or artificial (by vaccination). However, if production poultry has never been exposed to a virus, they immune system is defenseless against those new pathogens.

Important viruses in migratory birds

Research on viruses in migratory birds is constant due to the importance and lack of knowledge about these processes. Among the most important viruses in migratory poultry are avian influenza, West Nile virus, Marek’s disease, Newcastle virus and avian infectious bronchitis.

Avian Influenza

Avian influenza virus is perhaps one of the most important viral pathogens in poultry worldwide. This disease is widely studied for its impact on public health and transmission to swine and humans.

Migratory birds are recognized to have an important role in the spread of  avian influenza. It is highlighted that aquatic wild birds such as ducks are natural reservoirs of the disease. In these birds that also migrate, the influenza virus can have antigenic changes that increase the pathogenicity of the pathogen.

For this reason, studies have been made on the ecology and epidemiology of avian influenza. Some studies recognize an important role of migratory and wild birds in the mobilization of the virus that can be transmitted to poultry (Blagodatski et al., 2021).

In any case, these studies highlight the importance of continuing to study the behavior of avian influenza in migratory birds. Undoubtedly, this could better clarify the epidemiology of the disease in productive poultry.

West Nile Virus

In 2020, migratory birds in Malaysia were found to have antibodies against West Nile Virus (MY et al., 2020). This viral pathogen is transmitted by mosquitoes and can affect equines, humans, and other poultry. Migratory birds can harbor and amplify this type of virus to other birds such as layers and broilers. In addition, serological evidence of this virus has also been reported in migratory birds in Northern India, Bangladesh, and South Korea (A et al., 2020; JY et al., 2011; N et al., 2012).

Marek’s Disease Virus

Another study in 2011 detected the presence of Marek’s Disease Virus in migratory birds in Japan. The role of migratory ducks in the amplification of this viral pathogen had been recognized. In addition, they found that native ducks also had the presence of the virus and could be amplifiers towards other types of poultry (Murata et al., 2012). Marek’s disease could generate a systemic picture of malignant lymphoma that presents high morbidities if the strains involved are highly pathogenic.

Newcastle Virus

In addition, the Newcastle virus has also been reported in migratory poultry in Egypt (Hasan Mohammed et al., 2020). This is a highly contagious disease with respiratory and nervous signs of great impact in poultry farming.

Infectious Avian Bronchitis Virus (IBV)

In 2009, coronavirus genetic material was isolated by PCR from wild waterfowl in England. Sequence analysis of these viruses was later found to be consistent with Avian Infectious Bronchitis Virus. (Hughes et al., 2009)

Enhancing the immune response to viruses

Products such as natural immunostimulant pronutrients are available to enhance the immune system of poultry against viruses. Alquernat Inmuplus is a natural product composed of molecules of botanical origin that regulate and stimulate the immune system of poultry. This product does not generate a pharmacological effect but stimulates the animal’s physiology by activating gene expression and the production of ribosomal proteins. For these reasons, it is a safe product, does not create resistance, and leaves no residues.

In addition, these pronutrients can be administered to young and adult poultry. Furthermore, Alquernat Inmuplus strengthens the immunity of poultry against immunosuppressive diseases such as Gumboro Disease, Newcastle, and Infectious Bronchitis, among others. Finally, the product is recommended to improve the response to vaccination and reduce the use of antibiotics.

Conclusions

Migratory birds are species that perform migration processes during the year in different parts of the world. Due to the large number of individual birds involved in migration, it is of interest to know what diseases they can mobilize.

Viruses are a group of pathogenic agents of high impact in poultry farming due to the diseases they generate. Migratory birds can mobilize these viruses and generate mutations or infections that affect the production of poultry.

Avian influenza is one of the most studied avian viruses in history. However, there is no clear advice on the role of migratory poultry in the spread of this disease. Therefore, the role of these birds in the infection of other birds, such as production birds, is still being studied.

Finally, there are other viruses such as Marek’s disease, Newcastle disease, and West Nile virus that should be permanently monitored. There is evidence that these viruses have generated an immune response in exposed animals at some time, indicating the presence of the virus in the environment.