The human viral flu tends to spike in the winter for a major reason because of cold weather and the variations in temperature. The virus survives better in cool temperatures rather than hot climate. Similarly, the avian influenza outbreaks also increase in winter season in our country. As witnessed some out breaks of bird flu in the country. Therefore, let me focus only on occurrence of bird flu or Avian influenza outbreaks in winter and discuss the probable reasons for its appearance and spread.
Several outbreaks of severe bird flu in Europe and Asia have been reported in recent days to the World Organisation for Animal Health (OIE), is a sign the virus is spreading quickly again. Out breaks of AI in European countries, South east Asia, China and Japan.
According to a new research study, the risk of the introduction of bird flu virus on poultry farms is four times higher in the cold months of November to February than in the summer months (Sarah Mikesell 2020.The Poultry Site}.
This statement is true as several out breaks are reporting from many countries including our country also in the winter months.
What are the Winter months in India?
Winter Season is the coldest of the 6 seasons in India. It falls in the month of November, December and ends in March. The season is the largest and coldest season in India. In this climate, coolness is spread everywhere in the environment. The Himalayan range experience heavy snowfall during this season.
This season is favours the occurrence of bird flu in India as evidenced by recent out breaks of avian flu in many states.
As avian flu swept through India towards the end of 2020 and early 2021, states scrambled to step up vigil and measures to control the spread of the disease. The 2020/2021 outbreak, marked by the significant involvement and mortality of wild birds, has spotlighted the need for proactive monitoring of animal disease in the environment, conserving unprotected wetland habitats to curb disease spread, and addressing knowledge gaps like the wild waterfowl–poultry interface.
The latest bird flu outbreak in poultry and wild birds spanned 14 Indian states / Union Territories from Jammu and Kashmir in the north to Kerala in the south. Haryana, Maharashtra, Punjab, and Kerala were particularly severely affected. The latest outbreak involved highly pathogenic viral strains H5N1 and H5N8, according to the Indian government.
At least six Indian states have stepped up efforts to contain two strains of bird flu- H5N1 and H5N8 — in recent days after the deaths of thousands of migratory birds, ducks, crows and chickens.
Officials in Himachal Pradesh said carcasses were found over the past week at a Himalayan lake that witnesses large flocks of migratory birds during the winter season.
The mass deaths came amid a cull of nearly 35,000 poultry in Kerala, where an H5N8 virus outbreak killed up to 12,000 ducks. Authorities said the slaughter was ordered within a one kilometer (0.6 mile) radius of the infection epicenter.
In Haryana state authorities said nearly 150,000 chickens died mysteriously across several poultry farms in Barwala district. Neighbouring Punjab also reported similar deaths. More than 20 farms said their flocks were wiped out by an “unknown disease” and samples have been sent to labs for testing.
Rajasthan and Madhya Pradesh have also reported hundreds of crow deaths caused by H5N1 and H5N8 over past weeks. This state experienced that nearly 4,500 crows and herons died over several months from avian flu.
During 24th January, 2021 outbreaks of Avian Influenza (Bird flu) have been confirmed in 9 states (Kerala, Haryana, Madhya Pradesh, Maharashtra, Chhattisgarh, Uttarakhand, Gujarat, Uttar Pradesh and Punjab) for poultry birds and in 12 states (Madhya Pradesh, Haryana, Maharashtra, Chhattisgarh, Himachal Pradesh, Gujarat, Uttar Pradesh, Uttarakhand, Delhi, Rajasthan, Jammu and Kashmir and Punjab) for Crow/Migratory/Wild birds,” the ministry of animal husbandry said in a statement.
Why avian flu spread in winter months?
The upsurge of HPAI H5N1 epizootic waves has been linked to changes in agricultural practices, intensification of the poultry sector, and globalisation of trade in live poultry and poultry products.
The unprecedented spread of H5N1 or novel avian influenza A viruses (AIV) has been the interaction between migrating waterfowl and domestic poultry .
Reasons for spread of AI
- Pressure from urbanisation and pollution. With the loss of habitat and increase in poultry, the wild bird and poultry buffer has reduced and increased interaction and exchange of viruses.
- Local poultry birds, and in equipment (fomites) movement between farms and from the farms to wetlands and to markets.
- Domestic birds in an infected area are interacting with wild birds and some of these birds may be resident or migratory; the environment can be infected so these interactions happening in an area where there is an infection.
- In the Indian context, poultry plays a huge role in circulating the virus throughout the year in the form of LPAI.
- There was evidence of interaction between local poultry and wild waterfowl concerning H5N1 outbreaks.
- H5N1 outbreak occurrence was higher with greater proximity specifically to lakes, rivers, and coastal wetlands.
Most of the wild birds dead were Central Asian high-altitude bar-headed geese — one of the world’s highest flying birds — that migrate to South Asia in their thousands during the winter season.
Although wild birds are a natural reservoir of low pathogenic avian influenza (LPAI), we do not know if wild birds are a permanent reservoir of highly pathogenic avian influenza (HPAI) or how a LPAI virus transforms into a HPAI virus, one that poses a great threat to animal health and public health.
For such a fast and wide-spreading virulent pathogen, prediction based on changes of micro- and macro-environment.
Most of the H5N1 outbreaks were associated with a Siberian cold air mass dominating Eurasia. In winter and spring, such high pressure system moved fast and brought below-freezing temperatures, termed widely as “cold air outbreak” events.
The climate change on the ecology of avian influenza viruses (AI viruses), which presumably co-evolved with migratory water birds, with virus also persisting outside the host in subarctic water bodies. Climate change would almost certainly alter bird migration, influence the AI virus transmission cycle and directly affect virus survival outside the host.
Wild water birds form the natural reservoir of all influenza A virus. There is considerable genetic variability in terms of the different subtypes of AI viruses present in wild water bird populations, enhanced by continued re-assortment of the eight genetic segments present in the genome of the virions (for convenience, the virus subtypes are grouped by their hemagglutinin and neuraminidase viral antigens, HA and NA, respectively).
India has emerged as a global hotspot for HPAI H5N1, while also providing critical wintering habitat for many species of migratory waterfowl and year-round habitat for several resident waterfowl species. The country lies at the heart of Central Asian Flyway (CAF), which spans 30 countries and covers 279 populations of 182 migratory water bird species that rely on wetlands along the flyway, including the Pong Dam wetlands (Pong Lake Wildlife Sanctuary), a Ramsar site, where large scale mortalities of long-distance migratory birds such as bar-headed geese, first alerted biologists in December 2020.
Bar-headed goose (Anser indicus) is a long-distance migrant to the Indian subcontinent, with its major population breeding in China. There is a small breeding population in Ladakh, Mongolia, and Kyrgyzstan. Migrating bar-headed geese have been reported from many protected and non-protected wetlands of Assam, Himachal Pradesh, Jammu and Kashmir, Uttar Pradesh, Rajasthan, Andhra Pradesh, Odisha, Karnataka, Tamil Nadu, Kerala, and Maharashtra.
The distribution of AI viruses among wild birds is uneven, as it is influenced by both bird species and eco-geography. The general pattern is that most AI virus isolations are recorded in wild water birds, in the orders Anseriformes (in particular in the family Anatidae: ducks, swans and geese). These harbours the highest diversity and prevalence of AI viruses. Within the Anseriform order, the Anatidae family, and in particular the Anatinae sub-family has the highest prevalence and diversity of AI viruses. The mallard duck (Anas platyrhynchos) is the foremost AI virus host among the dabbling duck species. Wild ducks presumably form an important source of virus spill-over to poultry.
The persistence of AI viruses in duck populations on a year-round basis relies on the annual recruitment of large numbers of juvenile ducklings providing immunologically naïve hosts aiding viral replication, shedding and transmission.
Influenza A viruses can survive:
- 18 h. at 42 °C, 24 h. at 37 °C, 5 days at 24 °C and 8 weeks at 4 °C in dry and wet faeces,
- Over 30 days at 0 °C (32.0 °F) (over one month at freezing temperature)
- 6 days at 37 °C (98.6 °F) (one week at human body temperature)
- decades in permanently frozen lakes
- on hard non-porous surface such as plastic or stainless steel for 24–48 hours
- on clothes, paper and tissues for 8–12 hours
The present outbreak of AI in kerala is all probably from its existence of enormous duck population. The virus spread from wild ducks to domestic ducks and then spillover to poultry.Also important for the sustenance of the transmission cycle is the survival of the virus outside the host, in water. Water facilitates faecal–oral transmission, enables survival of virus in the absence of hosts, and helps to redistribute viruses among different hosts.
AI viruses are naturally transmitted through the faecal–oral route it helps when viruses can survive for weeks or months in cold water, and for many years in ice bodies. It has been proved that the AI viruses were isolated from ice in lakes in Siberia at a time when wild birds had already moved out of the region. Hence, virus persists outside the host in the subarctic breeding areas after the birds depart for their autumn migration and is still present when the birds return the following spring. The breeding season in subarctic Siberia is usually very brief, as migratory bird populations start migrating southward with their newborn juveniles to escape the first frosts, already arriving in pre-migration staging areas from mid-summer onward.
There are also ample variations in migratory behaviour among Anatidae species, even within populations. In general terms, the proportion of migratory species and the extent of migratory behaviour depend on the climatic conditions. In areas with harsh, cold climates most bird species migrate during the autumn to escape the frost. Areas further southwards, with higher temperatures or even subtropical climates, show a proportionally higher number of resident bird species.
AI viruses usually cause subclinical infections in their migratory water bird hosts, and during their stay in the wintering sites the prevalence of infection is usually lower than 5%.
It is found that H5N1 outbreak occurrence was higher with greater proximity specifically to lakes, rivers, and coastal wetlands. As in case of Kerala, Odisha, west Bengal and Northeastern states. These findings provide specific points in the landscape that may be good targets for interrupting the cycling of avian influenza viruses.
Highly pathogenic avian influenza is a poultry disease evolving from low pathogenicity AI virus circulating in wild birds and introduced in terrestrial poultry of sufficient flock size or density. Infection of wild birds by HPAI H5N1 viruses is the result of spill-back of HPAI virus from domestic to wild birds. The HPAI H5N1 panzootic is atypical in that wild birds have probably been involved in the spread of the disease.
Now is the time to start planning interventions aimed at preventing the introduction of Avian influenza virus in the winter. Adoption of strict Biosecurity practices may help prevent ion of the spread of infections.
Effective biosecurity requires that you isolate your birds from anything that could transmit a disease, such as AI, to the birds. The following are basic biosecurity measures:
- Secure poultry houses against wild birds, pets, and livestock.
- Restrict visitor access to poultry houses and coops.
- Have dedicated shoes or rubber boots for use in the poultry house.
- Establish a rodent and insect control program.
- Do not visit other flocks of poultry and then enter your poultry house without first washing and disinfecting thoroughly.
- Do not go into a poultry house after contact with any other birds (waterfowl, wild birds, pet birds, other show flocks or backyard flocks). This includes contact with birds during winter season.
- Thoroughly wash and disinfect any shared equipment before transferring between premises (scales, pens, feeders, drinkers, etc.).
- If there is any increase in sick or dying birds, seek veterinary assistance immediately.
Conclusion
In conclusion, it is thought that the biggest change in AI epidemiology resulting from climate change will be brought about by changes in the distribution, composition and migration behaviour of wild bird populations that harbor the genetic pool of AI viruses and in which natural AI transmission cycles take place. In contrast, HPAI, which remains largely confined to domestic poultry, has been spreading worldwide successfully in a very wide range of climatic conditions.
Prof. R.N. Sreenivas Gowda
Former Vice Chancellor KVAFSU, Bidar, Former Director,
IAH & VB, Bangalore Forer Prof and Head,
Dept of Pathology, Veterinary College, Bangalore