Media Reports: Bird Flu (H5N1?) In Turkish Poultry

 

UPDATE: 05/04  0500hrs EDT:  The FAO has posted a notice of this outbreak, albeit with very few details and no ID on the subtype.

 

 

# 10,002

 

 

It has been seven years since Turkey last reported HPAI H5N1 to the OIE (see Immediate notification), but Turkish officials well remember the impact the virus had in the years between 2006 and 2008, when roughly 200 outbreaks were recorded, along with a dozen human infections and four deaths.

 

When H5N1 began its big expansion out of Southeast Asia in 2005-06, Turkey was one of dozens of countries suddenly thrust into the battle against bird flu, and the quarantining towns has often been part of their playbook (see  2007 Turkey: Three Villages Quarantined?  & Turkey : 4 More Villages Quarantined,  & 2008 Turkey Quarantines Three Villages).

 

A pattern which should make today’s headlines and story a bit less urgent sounding that it might at first appear.  It should also be noted that according to these reports, poultry deaths have been ongoing in this town for several months.

 

In any event, overnight the Turkish language press has been carrying numerous reports of bird flu (`kuş gribi’ for those who would like to do a Google search) – presumably H5N1 -  having been detected in the Banda District of Balikesir, Turkey. 

 

I’ve not found any official statement,  but this being a weekend, that isn’t terribly surprising.  Hopefully we’ll get an official notification from the OIE or the FAO in the next day or two.

 

A few links below, followed by an English Language report from the Today’s Zaman.

 

He Quarter Bird Flu Quarantine of Receipt  ...

BALIKESİR ' BIRD FLU QUARANTINE POULTRY BAN '  

Bird flu quarantine began 
  

 

Turkish town put under quarantine after bird flu outbreak

May 03, 2015, Sunday/ 14:25:59/ TODAYSZAMAN.COM / ISTANBUL

A town in the bandırma district of the province of Balıkesir has been put under quarantine after officials confirmed the existence of bird flu in chickens there. Access to the neighborhood has been restricted to official vehicles only.

According to the Doğan news agency, the Bandırma Directorate of Food, Agriculture and Livestock launched an investigation in Bandırma's Edincik neighborhood over the death of around 40,000 chickens in four months. Samples from the chickens were sent to the Ministry of Food, Agriculture and Livestock's laboratory in İstanbul's Pendik district, where tests found that the mass deaths of the chickens was due to bird flu.

In a statement regarding the issue on Saturday, district governor Ali Mantı said security measures have been increased at the farms where the deaths took place and that chickens there were euthanized.

“Entering and leaving the region has been prohibited except for official vehicles. The samples were sent to the laboratory in Pendik. According to the tests, bird flu was detected. All protection measures have been taken in the farms where bird flu was detected,” Mantı said, adding cleaning was also done after chickens were culled and destroyed.

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Given the multiple reports of H5N1 being detected in migratory birds and occasionally poultry  in Eastern Europe (see OIE: H5N1 Kills 21 Pelicans In Bulgaria & Russia Reports H5N1 In Migratory Birds) – all sharing the same Black Sea / Mediterranean Migratory Flyway – it wouldn’t be terribly surprising for find Turkey added to the list.

 

Major Global Migratory Flyways – Credit FAO

 

Since last fall we’ve seen HPAI H5 virus on the move around the world, with H5N8 making it to North America and Europe, and H5N1 showing up in countries that haven't reported outbreaks since 2006-2007. 

 

Although the emergence of several new (H5N8, H5N2) HPAI viruses - more easily carried by wild and migratory birds -  are undoubtedly part of the reason behind this increased activity, for reasons that are less clear, H5N1 is on the move again as well.

 

For more on the spread of avian viruses across long distances by migratory birds, you may wish to revisit:

 

Erasmus Study On Role Of Migratory Birds In Spread Of Avian Flu

PNAS: H5N1 Propagation Via Migratory Birds

EID Journal: A Proposed Strategy For Wild Bird Avian Influenza Surveillance

PLoS One: North Atlantic Flyways Provide Opportunities For Spread Of Avian Influenza Viruses

APHIS: 2 More Minnesota Turkey Farms Hit By H5N2

 

# 9995

 

The USDA’s APHIS has announced that two more Minnesota farms have been hit by the Highly Pathogenic H5N2 virus, bringing to 7 the number commercial flocks hit so far in that state.  Stearns county, with three farms now reporting the virus, has been the hardest hit.

 

For now – in North America, anyway – the biggest concerns lie with poultry producers. 

 

While related to the H5N1 virus – which has killed several hundred people around the globe – these particular H5 viruses (H5N2 & H5N8) have not demonstrated a similar ability to infect and sicken humans. The CDC is taking a cautious approach to all of of these recently arrived HPAI viruses, however,  and has issued guidance for the testing, and prophylactic treatment of those exposed. 

 

 

USDA Confirms Highly Pathogenic H5N2 Avian Influenza in 3rd Stearns County, Minnesota Commercial Turkey Flock

Last Modified: Apr 6, 2015

 

CDC considers the risk to people from these HPAI H5 infections in wild birds, backyard flocks and commercial poultry, to be low

WASHINGTON, April 06, 2015 -- The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) has confirmed the presence of highly pathogenic H5N2 avian influenza (HPAI) in a third commercial turkey flock in Stearns County, Minnesota.  This is the sixth confirmation in a commercial flock in Minnesota.  The flock of 76,000 turkeys is located within the Mississippi flyway where this strain of avian influenza has previously been identified. CDC considers the risk to people from these HPAI H5 infections in wild birds, backyard flocks and commercial poultry, to be low.  No human infections with the virus have been detected at this time.

This flock is in the control area for a previous detection.   As part of our response protocol, samples were tested by the University of Minnesota Veterinary Diagnostic Laboratory as part of our standard surveillance work. The APHIS National Veterinary Services Laboratories in Ames, Iowa confirmed the findings. APHIS is working closely with the Minnesota Board of Animal Health on a joint incident response. State officials quarantined the premises and birds on the property will be depopulated to prevent the spread of the disease. Birds from the flock will not enter the food system.

(Continue . . .)

USDA Confirms Highly Pathogenic H5N2 Avian Influenza in Kandiyohi County, Minnesota Commercial Turkey Flock

Last Modified: Apr 6, 2015

 

CDC considers the risk to people from these HPAI H5 infections in wild birds, backyard flocks and commercial poultry, to be low

WASHINGTON, April 06, 2015 -- The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) has confirmed the presence of highly pathogenic H5N2 avian influenza (HPAI) in a molting breeder replacement turkey flock in Kandiyohi County, Minnesota.  This is the seventh confirmation in a commercial flock in Minnesota.  The flock of 26,000 turkeys is located within the Mississippi flyway where this strain of avian influenza has previously been identified. CDC considers the risk to people from these HPAI H5 infections in wild birds, backyard flocks and commercial poultry, to be low.  No human infections with the virus have been detected at this time.

Samples from the turkey flock, which experienced increased mortality, were tested at the University of Minnesota Veterinary Diagnostic Laboratory and the APHIS National Veterinary Services Laboratories in Ames, Iowa confirmed the findings. APHIS is working closely with the Minnesota Board of Animal Health on a joint incident response. State officials quarantined the affected premises and birds on the property will be depopulated to prevent the spread of the disease. Birds from the flock will not enter the food system.

(Continue . . . )

Although migratory birds are viewed as the primary suspects in the spread of these avian viruses, exactly how they are managing to infect commercial flocks in California, Minnesota, Missouri, and Arkansas hasn’t been determined.  

 

This update today from the USDA.

 

Update on Avian Influenza Findings

Last Modified: Apr 6, 2015

Print

Since December 2014, the United States Department of Agriculture has confirmed several cases of highly pathogenic avian influenza (HPAI) H5 in the Pacific, Central, and Mississippi flyways (or migratory bird paths). The disease has been found in wild birds, as well as in a few backyard and commercial poultry flocks. The Centers for Disease Control and Prevention (CDC) considers the risk to people from these HPAI H5 infections to be low. No human cases of these HPAI H5 viruses have been detected in the United States, Canada, or internationally.

Poultry Findings Confirmed by USDA’s National Veterinary Services Laboratories Include:

Captive Wild Bird Findings Confirmed by USDA’s National Veterinary Services Laboratories:

Wild Bird Findings confirmed by USDA’s National Veterinary Services Laboratories are available here.

Surveillance for avian influenza is ongoing in commercial poultry operations, live bird markets, and in migratory wild bird populations.

USDA is coordinating closely with its partners, including Arkansas, California, Idaho, Kansas, Minnesota, Missouri, Nevada, Oregon, Utah and Washington State officials, the U.S. Department of the Interior and the U.S. Department of Health and Human Services, on avian influenza surveillance, reporting, and control efforts.  The United States has the strongest AI surveillance program in the world, where we actively look for the disease and provide 100% compensation to affected producers to encourage reporting.

USDA continues to inform OIE and international trading partners of these findings.  USDA is working with trading partners to minimize trade impacts on poultry and poultry products as much as possible.

All bird owners, whether commercial producers or backyard enthusiasts, need to continue practicing good biosecurity, preventing contact between their birds and wild birds, and reporting sick birds or unusual bird deaths to State/Federal officials, either through your state veterinarian or through USDA’s toll-free number at 1-866-536-7593.  Additional information on biosecurity for backyard flocks can be found at healthybirds.aphis.usda.gov

USDA emphasizes that poultry, poultry products and wild birds (see biosecurity and wild birds) are safe to eat if they are properly handled and cooked to a temperature of 165 degrees Fahrenheit.

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Kansas Dept. Agriculture: LPAI Bird Flu At Commercial Turkey Farm

Crawford County – Credit Wikipedia

 

# 9864

 

 

Although the subtype isn’t mentioned in the press release, today Kansas authorities have announced the detection of a low pathogenic avian flu at a commercial turkey farm in Crawford county, on the border with western Missouri.

 

Culling has been ordered and the carcasses will be buried on site.

 

Two weeks ago Missouri reported two HPAI outbreaks in Turkeys (see Missouri Dept. Ag. Statement On Avian Flu At Missouri Turkey Farm) while Arkansas to the south reported (HPAI H5N2 Confirmed In Arkansas Turkey Flock) a couple of days later.

 

Low Path (LPAI) strains are viewed as being much less serious than HPAI strains – and often only cause minor illness in birds – but need to be quickly contained because LPAI H7 and H5 viruses have the potential to evolve into highly pathogenic strains.

 

This from the Kansas Department of Agriculture.

 

 

Low Pathogenic Avian Influenza case confirmed in Crawford County

MANHATTAN, Kansas – The Kansas Department of Agriculture was notified Tuesday that samples collected from a commercial poultry flock in Crawford County tested positive for low pathogenic avian influenza (LPAI).

The flock will be depopulated on Thursday by company officials and buried on site.  Working in conjunction with the Kansas Department of Health and Environment, a disposal area has been identified.  This area has been determined to be acceptable for the burial of the livestock carcasses based on data evaluated including groundwater depth, soil type, depth to bedrock and slope of land in the area.  KDHE will monitor the disposal site as part of their normal inspection of the facility.

Because this is LPAI, as opposed to Highly Pathogenic Avian Influenza (HPAI), no quarantine will be issued by KDA. 

“We are dedicated to providing the necessary assistance and precautions to avoid any possible spreading of the disease,” Dr. Bill Brown Kansas Animal Health Commissioner said.  “Even though this is the low path variety, it still requires immediate action and animal health officials are responding.”

Symptoms of avian influenza in poultry include coughing, sneezing, respiratory distress, decreased egg production and sudden death.  

If you suspect your flock has contracted the disease, quarantine the affected animals immediately.  Infected animals must be humanely destroyed and disposed of properly to prevent the disease from spreading. 

Although vaccines are available, they are not commonly used because no vaccine covers all 15 strains of the disease.  Prevention is the best way to combat Avian Influenza.  Keep wild birds away from your home or farm, and stay informed about the health of neighboring animals. 

For more information please check www.agriculture.ks.gov/avianinfluenza

 

UK: H1N1 `Swine’ Flu Found In Turkeys

 

 

 

# 5224

 

 

From Defra (Department for Food and Rural Affairs) in the UK this morning, we learn that turkeys on a farm in Cheshire have tested positive for an H1N1 virus `closely similar’  to the 2009 pandemic strain.

 

Although we’ve seen a few instances of turkeys (and cats, dogs, ferrets, and even cheetahs) infected with the 2009 H1N1 swine flu virus, this is the first detection I’ve seen of the swine flu virus among poultry in the UK.

 

A few past blogs on the slightly promiscuous nature of this swine H1N1 influenza strain include:

 

US: Dog Tests Positive For H1N1

US: Turkey Farm Reports H1N1

Study: H1N1 And Birds

Cat Got Your Virus?

 

 

The Defra news release follows:

 

H1N1 found in turkeys

Published on Wednesday 12 January 2011 at 10:56am

A routine disease investigation has ruled out avian notifiable disease but detected H1N1 influenza in turkeys on a farm in Cheshire.

 

The strain is closely similar to the human pandemic H1N1 strain currently circulating.

 

The Health Protection Agency has undertaken a thorough public health risk assessment and can confirm there is no risk to public health.

 

This finding has resulted from a routine notifiable avian disease investigation relating to a small number of turkeys showing mild signs of disease. During the investigation there was clinical improvement in these birds.

 

Results of laboratory tests show that statutory notifiable avian disease – where the government would need to take animal health action – can be ruled out. Restrictions have been lifted on the farm.

 

There is no food safety risk. Pandemic H1N1, in common with avian influenza, has not been shown to be transmissible to people through eating properly handled and cooked poultry meat, products and eggs.

 

Bird keepers should continue to maintain appropriate biosecurity measures and be vigilant for signs of notifiable avian disease and report any suspicion promptly to the Animal Health agency.

Notes

1. Pandemic H1N1 2009 has been confirmed in poultry in other countries around the world including the USA, Canada, Chile and France.
2. Influenza viruses have been shown to infect a great variety of birds. In poultry, influenza causes two distinct clinical forms: highly pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI). HPAI leads to serious disease in almost all poultry species resulting in large numbers of deaths. It is caused by some viruses of H5 or H7 subtypes. LPAI viruses belong to all H subtypes and only cause mild limited infection.  
3. The UK maintains a programme of surveillance of avian influenza in domestic poultry and wild birds found dead.
4. When statutory notifiable avian disease is confirmed action to confine and stamp out disease includes movement controls on susceptible species in the area around  the premises, enhanced biosecurity, culling of susceptible poultry on the premises  and cleansing and disinfection of the premises.

 

 

Given the tendency for H1N1 to appear as a mild, LPAI infection in gallinaceous poultry (such as  grouse, turkeys, pheasants and quail), poultry infections like this one probably happen more often than we are aware.

OIE Report: Manitoba Bird Flu Identified As H5N2

 

 

 

# 5091

 

 

My thanks to Ironorehopper on FluTrackers for posting the link to this OIE notification detailing the avian flu outbreak at a turkey farm in Rockwood, Manitoba.

 

I’ve excerpted part of the report below.

 

 

Low pathogenic avian influenza (poultry), Canada

Information received on 25/11/2010 from Dr Brian Evans, Chief Food Safety Officer/Chief Veterinary Officer, Office of the President, Canadian Food Inspection Agency, OTTAWA, Canada

New outbreaks

Outbreak 1 (NAI-2010-MB-001)
Rockwood municipality, MANITOBA

Date of start of the outbreak
17/11/2010

Outbreak status
Continuing (or date resolved not provided)

 

Affected Population

Turkey breeders farm, with four barns on site. Barn 1 is empty, barn 2 contains 600 toms (approx.), barn 3 contains 3,000 hens (approx.) and barn 4 contains 3,800 hens (approx.). The hens in both barn 3 and 4 are 44 weeks old and were lethargic with a 45% decrease in egg production but the egg production has improved since the start of the event. No respiratory disease was observed. The mortality in the flock has not increased.

Epidemiology

Source of the outbreak(s) or origin of infection

• Unknown or inconclusive

Epidemiological comments

This is the first outbreak of Notifiable Avian Influenza (NAI) detected in the province of Manitoba.

The farm has been quarantined by the Canadian Food Inspection Agency (CFIA) and investigation will be conducted in compliance with the Canada's Notifiable Avian Influenza Hazard Specific Plan. A stamping out policy will be applied.

Preliminary results from the National Center for Foreign Animal Diseases in Winnipeg indicate the presence of a H5N2 subtype avian influenza virus (PCR).

Sequence analysis of the PCR products indicates that the cleavage site is consistent with low pathogenic avian influenza virus H5. Closest matches (99% identity) in Genbank are to North American H5N2 viruses from wild birds.

Virus isolation is underway and additional testing is to come, including the intravenous pathogenicity index test.

NAI surveillance has been in place in domestic poultry in Canada for many years and this outbreak is limited to the province of Manitoba.

Note by the OIE Animal Health Information Department: H5 and H7 avian influenza in its low pathogenic form in poultry is a notifiable disease as per Chapter 10.4. on avian influenza of the Terrestrial Animal Health Code (2010).

Control measures

Measures applied

• Quarantine
• Movement control inside the country
• Screening
• Vaccination prohibited
• No treatment of affected animals

Measures to be applied

• Stamping out
• Disinfection of infected premises/establishment(s)

CFIA Statement On Manitoba’s Avian Flu Outbreak

 

 

# 5087

 

The CFAI (Canadian Food Inspection Agency) has released the follow statement on the detection of bird flu on a Manitoba turkey farm.

 

As opposed to the earlier news story out of Winnipeg, no mention of the strain is made in this release.

 

 

CANADIAN FOOD INSPECTION AGENCY

Nov 24, 2010 17:00 ET

Canadian Food Inspection Agency: Avian influenza Confirmed in Manitoba

OTTAWA, ONTARIO--(Marketwire - Nov. 24, 2010) - The Canadian Food Inspection Agency (CFIA) has confirmed the presence of an avian influenza virus in a commercial poultry operation in the Rural Municipality of Rockwood, Manitoba.

 

Further testing is underway to determine the precise subtype and pathogenicity of the virus. Pathogenicity refers to the severity of the illness caused in birds. Clinical assessment and laboratory analysis to date suggests this is likely a low pathogenic virus.

 

Avian influenza viruses do not pose risks to food safety when poultry and poultry products are properly handled and cooked. Avian influenza rarely affects humans, unless they are of specific types and there has been close contact with infected birds.

 

All birds on the infected premises will be humanely euthanized and disposed of, in accordance with provincial environmental regulations and internationally accepted disease control guidelines. Once all birds have been removed, the CFIA will oversee the cleaning and disinfecting of the barns, vehicles, equipment and tools to eliminate any infectious material that may remain.

 

The CFIA is conducting a thorough epidemiological investigation, including tracing any recent movement of birds, bird products and equipment onto and off of the infected property. To limit any potential virus spread, the CFIA is also applying restrictions on the movement of poultry and poultry products within three kilometres of the infected premises.

 

Animal health and public health authorities from the Province of Manitoba, local poultry specialists and industry are actively collaborating on the response to avian influenza in the Manitoba poultry operation, and in supporting the producer.

 

All poultry owners are urged to take an active role in protecting their flocks. This includes employing strict biosecurity measures on their property and immediately reporting sick or dead birds to their veterinarian or the nearest CFIA office. Further information on biosecurity is available on the CFIA website at www.inspection.gc.ca/biosecurity.

 

The CFIA is notifying the World Organisation for Animal Health (OIE) and international trading partners of this situation.

 

New information will be provided to the public as it becomes available.

 

For information on safe food handling, please visit: http://www.inspection.gc.ca/english/fssa/concen/concenrol/rolsafe.shtml

 

For more information, please contact

Canadian Food Inspection Agency
Media Relations
613-773-6600

 

CTV Reporting Low Path H5 On Canadian Turkey Farm

 

 

# 5086

 

 

Although first announced several hours ago, details remain sketchy on the type avian flu strain detected in number of turkeys at a farm in the rural municipality of Rockwood, Manitoba.

 

CTV Winnipeg is reporting this as an H5 strain, likely low path, and not the highly pathogenic H5N1.

 

Other media outlets are not specifying a strain, so these details could change or evolve over the next few hours. 

 

A hat tip to Ironorehopper on FluTrackers who posted the following report.   An ongoing thread (started by Shiloh) tracking new developments is available at this link.

 

 

 

Turkeys in RM of Rockwood test positive for form of bird flu, officials believe strain is non-deadly

Officials have not yet said how many of the animals tested positive for an H5 strain of bird flu.

Updated: Wed Nov. 24 2010 14:19:36
ctvwinnipeg.ca

Provincial and federal officials have quarantined a turkey farm in the RM of Rockwood.

 

Some turkeys have tested positive for an H5 strain of bird flu, but there is no evidence it is the deadly form known as the Asian strain of the H5N1 influenza, said provincial officials.

 

There has been no indication of human illness.

(Continue . . .)

 

 

Low path outbreaks of avian influenza have been recorded in North America (and around the globe) in the past, and rarely present a human health threat.

 

CIDRAP’s overview on avian influenza Avian Influenza (Bird Flu): Agricultural and Wildlife Considerations  details many of these outbreaks.

 

Low Pathogenic avian viruses, if left  unchecked, have the potential to mutate into a more highly pathogenic strain. For that reason low path outbreaks of the H5 and H7 variety are taken seriously, and are a reportable disease to the OIE.

 

Culling is generally the recommended response.

US: Turkey Farm Reports H1N1

# 4104

 

 

 

It was only last month that that a study in Eurosurveilance sought to reassure us that Turkeys weren’t particularly susceptible to the H1N1 virus.   

 

Below is just an excerpt.

 

Eurosurveillance, Volume 14, Issue 41, 15 October 2009

Rapid communications

Resistance of turkeys to experimental infection with an early 2009 Italian human influenza A(H1N1)v virus isolate

C Terregino¹, R De Nardi¹, R Nisi¹, F Cilloni¹, A Salviato¹, M Fasolato¹, I Capua ()¹

 

Our findings suggest that in its present form, the pandemic H1N1 influenza virus is not likely to be transmitted to meat turkeys and does therefore not represent an animal health or food safety issue for this species.

 

 

Despite this study (which has an excellent pedigree in Ilaria Capuam, noted virologist for the OIE/FAO in Italy), over the past few months we’ve had reports of infected turkeys in Chile (see FAO: Concerns Novel H1N1 May Spread In Poultry  and   Chile: H1N1 Jumps To Turkeys) and Canada  (see Update On Ontario H1N1 Infected Turkeys).

 

Now, a US turkey farm in the the state of Virginia is reporting an H1N1 infection in a flock.   A hat tip goes to Indigo Girl on Allnurses pandemic forum and celvin11 on FluTrackers for the link.

 

This report from Reuters. 

 

U.S. finds pandemic H1N1 virus in turkey flock

 

Mon Nov 30, 2009 5:53pm EST

WASHINGTON (Reuters) - The pandemic H1N1 flu virus was confirmed in a flock of breeder turkeys in Virginia -- the first U.S. case involving turkeys, the U.S. Agriculture Department said on Monday.

 

The virus also has been found in hogs, three house cats, pet ferrets and a cheetah in California. USDA said infections of turkeys have been reported in Canada and Chile.

 

"This is the first detection of 2009 pandemic H1N1 influenza in turkeys in the United States," said a USDA spokesperson.

(Continue . . . )

 

We’ve chronicled a number of species jumps involving the H1N1 virus, and the Reveres at Effect Measure took on the subject of promiscuous flu viruses in their blog today  (see Dogs, cats and swine flu's promiscuity).

 

I confess I’m unaware of the `cheetah story’ alluded to in the above story, and a quick Google search didn’t turn up anything. 

 

We will no doubt be reminded by the USDA that these infections pose no food safety issues, but the ultimate threat of an ever widening host range for the H1N1 virus is less clear. 

There are a couple of trains of thought here.  

 

One is that when the virus broadens its host range, it has more opportunities to mutate or to reassort with other viruses. 

 

One might, after all, reasonably expect that the H1N1 virus has a better chance to meet up and reassort with an H5 or H7 avian virus in a turkey, than in a human host. 

 

There is another theory, however, that states that viruses don’t tend to mutate as long as they have a large number of susceptible hosts.

 

Virologist John Oxford has suggested that mutations in the H1N1 virus are less likely to occur until a certain amount of herd immunity is achieved. There have been studies that indicate that vaccination pressure may actually drive antigenic drift in flu viruses.

 

Avian influenza: genetic evolution under vaccination pressure

Magdalena Escorcia, Lourdes Vázquez, Sara T Méndez, Andrea Rodríguez-Ropón, Eduardo Lucio and Gerardo M Nava

Virology Journal 2008, 5:15doi:10.1186/1743-422X-5-15

 

As a population gains herd immunity (through vaccines or exposure), the virus must either evolve (mutate) away from the established immunity or die off for a lack of suitable hosts.

 

But, if the virus has a wider host range (say humans, pigs, and birds), or a ready natural reservoir, then there is less evolutionary pressure on it to mutate.  

 

Of course this second theory doesn’t help much with relatively rare, but major antigenic shifts (reassortments), but deals mostly with the far more common antigenic drift (minor mutations).

 

Which theory is correct?

 

It’s entirely possible that both are correct, as they are not mutually exclusive. 

 

As to what happens with this promiscuous pandemic H1N1 virus? 

 

That’s the $64 question, and no one has a good answer yet. 

 

Stay tuned.