Avian Influenza and Poultry Notifiable Disease

What is a notifiable disease?

A notifiable disease is one that must be reported to the Animal and Plant Health Agency (APHA)- as soon as there are any suspicion that it may be present

It can be endemic in the UK, such as bovine TB or exotic e.g. food and mouth disease

Why is a disease “made” notifiable?

Three main reasons:

• International trade

Many notifiable diseases will result in trade restrictions. World Organisation for Animal Health (WOAH) maintains a list of countries free of certain diseases, including avian influenza

• Animal health and welfare

Highly infectious and destructive/ debilitating diseases with significant economic impact

• Public health

Some notifiable diseases are potentially severe zoonoses

What happens if a notifiable disease if suspected?

*Compensation- compensated for alive animals only, animals that have already died of disease don’t get compensated for

Notifiable avian disease

• Avian influenza virus

• Newcastle disease virus

*Can affect: chickens, ducks, turkeys

Avian Influenza

Orthomyxoviridae (-ve sense, ssRNA virus)

• Influenza virus A

Influenza A variants can be named according to host species (e.g. ‘bird flu’, ‘swine flu’)

Standard naming: Influenza A/ turkey/ Turkey/ 1/05 (H5N1)

(Strain/ species/ country/ ??/ year)

May also be named according to pathogenicity, esp. in poultry e.g. low pathogenic AI, highly pathogenic AI

Very prone to genetic CHANGE (RNA viruses- no ability to proofread so change in occurs a lot)

Emergence of new subtypes based on point mutations and genome reassortment

Influenza A virus

Causes severe respiratory disease in humans and other animals

Epidemic (seasonal) or pandemic outbreak in humans

Classified on basis of viral surface proteins:

• Haemagglutinin (HA or H)

• Neuraminidase (NA or N)

• Antibodies to HA are mostly responsible for virus neutralisation (NA less so)

Influenza A virus evolution- Antigenic drift

RNA- dependent RNA polymerase that copies the viral genome makes an error roughly 1/ 10,000 nucleotides

10kb is the approximate length of the influenza RNA genome

This genetic change leads to gradual change in encoded proteins and so called “antigenic drift”

Influenza A virus evolution- Antigenic shift

Segmented genome (8 separate segments of vRNA)

Allows mixing or reassortment of vRNAs if more than 1 type of influenza virus infects a single cell. Leads to sudden changes in virus genome which can change resulting proteins dramatically- antigenic shift.

Pandemic H1N1 2009 (swine flu 2009) virus is a previous triple reassortment of bird, pig and human flu viruses further combined with an Eurasian pig flu virus.

Avian influenza virus epidemiology

Aquatic birds especially ducks reservoir for most avian influenza viruses

Migratory waterfowl can spread virus (main cause)

Avian influenza isolates usually species-specific (enabling virus to change and adapt between species)

Replicates inside the intestinal tracts of birds then transmission is by the faecal oral route + aerosol

Can also cause respiratory infection

Severity of avian influenza

Pathogenicity varies between subtypes from low morbidity with low pathogenic viruses to 100% mortality with highly pathogenic viruses (HPAI)

HPAI H5N1 virus causing current outbreaks in UK

Highly pathogenic AI (HPAI)

• Sudden Death (upto 100% mortality in 72 hours)

• Reduced feed consumption

• Cessation of flock vocalisation

• Drop in production (egg or live weight gain)

• Depression

• Cough

• Cyanosis

• Diarrhoea

• Nervous signs- off thier feet

*off purple colour in wottle

Highly Pathogenic AI (HPAI)

What does it take to make a highly pathogenic AI virus?

• Highly pathogenic strains of AI are H5 or H7

• Pathogenicity associated with cleavage of HA (cf. NDV F protein)

*only able to be cleaved in gut or respiratory tract- EKTR- low pathogenic RKKREKR- can be cleaved anywhere- highly pathogenic

Can spread through whole body hence causing more problems

International definition of notifiable avian influenza

Avian influenza due to highly pathogenic H5 or H7 viruses

Avian influenza with an intravenous pathogenicity index (0-3) in 6 week old chickens greater than 1.2 or 75% mortality over 10 days.

Also: avian influenza due to low pathogenic H5 or H7 viruses

A notifiable avian influenza outbreak requires immediate implementation of control measures in most countries through national legislation.

*lots of low pathogenic diseases circulating, ability to become highly pathogenic- H5 or H7

On suspicion of HPAI

APHA notified by vet, farmer ect

Farmer must not move anything (live birds, manure etc) off premises

Birds cannot be brought onto premises

APHA vet examines birds, records etc (may rule out AI)

Premises declared a “suspect premises”

VI serves notice placing controls on movement of animals, eggs, vehicles etc.

Isolation of poultry from wild birds within buildings (free- range birds)

Deployment of disinfection facilities at entrance to premises and bird housing

Warning signs erected

Diagnostic testing for NDV or AIV

When is testing done?

2 main scenarios:

1- Outbreak of ND/ AIV is suspected (notifiable disease investigation)

• Samples may include swabs, tissue samples, cadavers

• Egg inoculation to grow and isolate virus

• RT- PCR diagnosis for virulence determinants (e.g. cleavage site)

2- For exclusion of ND or AIV as a possible diagnosis

• Cloacal and oropharyngeal swabs collected from ~20 birds

• Samples pooled and tested by rRT- PCR for avian influenza or paramyxovirus genes

Diagnostic tests for AI

Once disease is confirmed

Actions are initiated through the implementation of government contingency plans

Notification of infected status to WOAH (effects UK disease free status)

Actions at infected premises

Disease control zone

AI prevention zones- enhances biosecurity +/ - mandatory housing

Actions at infected premises

Culling- all poultry and any captive birds

Disposal- all carcases, eggs and any other contaminated material must be disposed of

Initial cleaning and disinfection (C&D) will be carried out by APHA

Health measures for exposed workers dependent on risk

Undertake secondary C&D and restock after further 21d or

Cease production and maintain biosecutiy for 12 months- suggestion that ~50% of flocks may do this!

Control zones around infected premises

HPAI (except H5N1 in poultry)

• Protection zone (PZ) 3km 21d

• Surveillance zone (SZ) 10km 31d

HPAI H5N1 in poultry

• Protection zone (PZ) 3km in 21d

  Highly restricted in terms of movement and biosecurity

• Surveillance zone (SZ) 10km 30d

  Similar but meat/ carcass can be removed

• Optional restriction zone (RZ) 30d

  No restrictions on movement of litter

Culling

Cull birds as soon as possible in a way that minimises risk of onward disease spread

Welfare of birds is subject to legal controls

Whole house gassing is preferred

Ventilation shutdown a last resort where there is a threat to public health and only permitted in England

Culling- whole house gassing (WHG)

WHG with CO2, where birds are killed in their production housing, is the preferred option. But not all poultry buildings are suitable for WHG due inadequate sealing.

Or the use of high expansion water- based foam to deliver an anoxic gas (nitrogen) intro poultry sheds.

*needs to be airtight for gassing, foam hard to clear up

Culling- containerised gassing unit

Birds are placed inside a standard industry transport module and loaded into a solid rectangular gas- tight steel container with a hinger door with 2 inlets for gas and 2 outlets through which air is displaced. The gas used is 80% argon and 20% CO2, this is commercially available throughout the world as it is used for welding.

When 2 CGUs are operated in tandem and operated to thier full potential, system is capable of killing 4-5000 birds per hour

Compensation

For poultry or other captive birds not diseased at the time of killing, compensation is payable at the value of the birds immediately before killing.

For poultry or other captive birds dead or diseased at the time of killing, no compensation is payable.

Amount of compensation determined from “rate tables”, depending on age of birds, broiler vs layer etc

Does not account for “consequential losses”

*Doesn’t take into account cleaning and disinfecting costs

*Doesn’t take into account cost of time not in production

Current UK situation

Ongoing outbreaks of H5N1 in poultry

Large number of cases of HPAI H5N1 in England since the H5N1 outbreak started in October 2021

An avian influenza prevention zone (AIPZ) including mandatory biosecurity measures is in force across England, Wales and Scotland

Some parts of England also require mandatory housing of birds

ALL poultry keepers must be registered with APHA

Rules in AIPZ

Strict biosecurity and hygiene including:

• Keep ducks and geese separate from other birds

• Prevent contact with wild birds and rodents

• Clean housing, equipment, vehicles and footwear

• Keep records of birds movements, death and eggs

• Additional rules if you keep more than 500 birds

• Housing required in some regions

Impact on wildlife

Large number of infected species including geese, ducks, seabirds, birds of prey- many deaths in previous years

Populations of rare and endangered species at risk

Vaccination against avian influenza

Why not usein UK?

Vaccination prohibited in ‘slaughter policy’ countries because of difficulty establishing freedom from infection

Vaccines effective against one subtype may not be effective against another

Live vaccines are not used due to risk of reversion to virulence

Vaccinated asymptomatic birds may still shed viruses

Used widely in some asian and South American countries

Permitted in UK for some birds in zoological collections

Influenza at the human- animal interface

Influenza viruses circulating in animals pose threats to human health e.g. avian influenza virus H5N1 and H9N2

Contact with infected animals at work

Live animal markets, close contact in “family situations”

Handling or slaughter of infected animals, or work with raw meat and by- products from infected animals

Contamination from faeces, blood etc.

Avian Influenza summary

Caused by influenza A viruses

Virus change through mutation and genome reassortment make effective vaccination very difficult

Strains are usually species specific but some risk of humans zoonosis and potential for human pandemic

Spread of AI facilitated by migration of wild birds

UK has control zone and slaughter policy

Newcastle disease virus

Avian paramyxovirus-1: affects chickens, ducks, pheasants, geese, turkeys

Shed in all excretions & secretions → aerosols

Virus stable for weeks on carcasses → mechanical transfer

Highly contagious

Affects all birds of all ages

Mortality rate variable: 50-100%

Common in wild birds- inapparent infection

Can cause mild conjunctivitis/ FLI in humans

*FLI is flu like illness

Newcastle disease virus

NDV strains vary in virulence and tropism:

• lentogenic- mild inapparent infection

• mesogenic- mild respiratory disease, some deaths in young birds

• neurotrophic velogenic- acute, severe, fatal with respiratory and nervous signs

• viscerotropic velogenic- severe, fatal with haemorrhagic lesions, respiratory disease

Determined by F glycoprotein

Newcastle disease virus

Membrane glycoproteins

HN- allows in and out

F- fusion

Newcastle disease virus

Fusion Protein

• Synthesised as inactive precursor (F0)

• Cleaved by host cell proteases to active forms (F1 and F2)- if not cleaved virus cannot enter!

• Lentogenic strains are confined to GI and respiratory tracts where trypsin- like proteases are present

• Velogenic stains can be cleaved in many tissues by ubiquitous (furin- like) proteases due to an altered cleaved site → contains multiple basic amino acids i.e. at least 3 Arg or Lys residues

Newcastle disease virus- previous UK outbreaks

1997- outbreak limited to 4 chicken flocks and 7 turkey flocks

2005- reared pheasant in Surrey*

2006- game birds in East Lothian (pigeon PMV- 1)

>10,000 birds slaughtered

Newcastle disease virus

Clinical findings

• Vary depending on virulence of the virus

• Depression, diarrhoea, oedema of the head, nervous signs, prostration, egg drop/ malformation

Watery yellow/ green diarrhoea

Shell malformation

Infected chickens with nervous sings

Haemorrhagic lesions

Newcastle disease virus- control

Biosecurity and other management techniques

Vaccination: most commercial flocks are vaccinated

• live attenuated virus, inactivated or vectored vaccines

Notifiable disease: slaughter in the event of a severe outbreak with velogenic virus