Swine Influenza elimination

Science

 

Swine Influenza does not have a carrier status.

The virus is not excreted after 7 days post-infection.

The virus rapidly dies in the environment.

Influenza viruses can be transmitted between pigs and man and back again.

Depopulation

1

Depopulation will remove the influenza virus.

2

The new source must be influenza free.

3

Note employees are a risk of bringing influenza onto the property.

4

Ideally, if the farm recently infected, all employees must have become positive or be vaccinated before the farm is restocked.

5

Note vaccination only provides temporary protection – in pigs around 6 months.

6

Vaccination is very strain specific – see vaccine pros and cons below.

Elimination in Nursery to Finish – separate unit pig enter from an uninfected site

1

Close unit.

2

No inputs of any pigs for minimum 2 weeks.

3

Euthanase all chronically cull sick pigs.

4

Sell all available animals that are well enough to travel.

5

Australian advantage as market pigs can go from 25 kg onwards.

6

Clinically sick pigs may not pass inspection because of high temperatures.  If the pigs are not sick there is no human risk from the meat.  Note infected pigs, however, may pose a risk to transport or slaughter personnel.

7

Place infected – sick – pigs into passageways or pens of all buildings.

8

Vital to infect all remaining pigs so the virus can die out on the farm.

9

Prepare autogenous vaccine.

10

Tonsilar scrape.

11

Nasal samples via Dacron swabs.

12

Place scrape and Dacron swabs into (phosphate buffered solution) PBS immediately after collection.

13

Influenza virus extremely labile.

14

Take samples from at least 10-20 infected animals depends on the number of animals to vaccinate.

15

Administer vaccine intramuscular and via direct nasal spray.

16

Use commercial vaccine is possible – note vaccines pros and cons below.

17

Place all pigs on the unit on Aspirin in the water – note withdrawal times.

18

Provide suitable antibiotic cover for secondary infections – chlortetracycline 400 g/tone for example – note withdrawal times.

19

After 14 days euthanase all remaining coughing pigs and chronic pneumonic pigs.

20

Introduce tagged negative influenza sentinel pigs throughout the farm.

21

Review all sentinel pigs 2 weeks later – clinical signs, antibody and nasal swabs.

22

If all sentinel pigs are negative – restart normal pig production.

23

Note human personnel – transport who move the weaners to the infected site.

 

 

Farrow to Wean farm or Farrow to Finish farm

 

This can be more complicated as colostrum interferes with pigs ability to contract influenza.

 

Farrow to weaning section

1

Close farm.

2

If gilts are in isolation (a negative) either brings into the farm, infect in isolation – from material from the farm, or keep in isolation until the main farm clear.

3

Cull or abort all pregnant sows which are due to farrow over the next 2 week period or euthanse at birth 2 weeks worth of pigs.  It is vital to produce a 2 week gap in production.

4

Off site farrowing would be possible, but these animals will need to be farmed separately until confirmed they are free of influenza virus.

5

Cull all chronically sick animals.

6

Expose all sows and farrowing sows and piglets with infected – sick – sows and gilts.

7

Prepare an autogenous vaccine using tonsillar scrapes and Dacron nasal swabs as above.

8

Vaccinate all sows, gilts, boars and piglets.

9

Place sows, gilts and boars on supportive antibiotics.

10

Ensure colostrum management is optimal.  Cull all runt and poor doing piglets and any pig which is suspected that it did not get colostrum.

11

Nursery pigs at weaning move to off-site nursery area.  They must not go to the normal nursery/finishing area.  It may be possible to early wean and move the nursery pigs to the nursery/finishing area which is then closed.  Sows which are early weaned can be kept in the pig flow using Regumate at weaning to prevent oestrus.  Regumate removed at expected weaning date.

12

Note if the farm breeds from on-farm boars, their fertility is likely to be sub-optimal for at least 6 weeks after infection.  Purchase off-farm AI.  Ensure all sows and gilts are mated with off-farm AI.

13

14 days later Cull all chronically coughing pigs.

14

Place sentinel gilts around the farm and test in 3 weeks as before.

                Weaned pigs – to new Off site area

15

All newly weaned nursery pigs to be placed off site for 2-3 weeks (note biosecurity issues – more complex in pig dense area) until the sow’s are confirmed free of influenza.

16

The current nursery and finishing operation requires a 2 week break in pigs – see control in nursery/finishing area.

17

If any pigs become sick with influenza, the sick pigs must be placed around the whole group.

18

If the animals become sick consider Aspirin and supportive antibiotics.

19

Vaccination at weaning might be considered, repeat at 6 weeks of age.  Colostrum antibodies may interfere until the pigs are 6 weeks of age.

20

Note gilts may provide poor colostrums protection.  All gilt litters should be spilt suckled at least once to ensure some adult sow colostrum has been consumed.  Alternatively cull all gilt litters.

21

These nursery pigs must remain in the isolated nursery until the youngest pigs are 10 weeks old.  These pig may or may not break with the influenza virus.

22

Place sentinel animals into the nursery group 3 weeks before the pigs are allowed to move to previous finishing operation.

23

Ideally finish these pigs as a separate group.

24

Sell all animals as soon as they reach a marketable weight – reduce the population as much as possible.  Australian advantage with multiple markets down to 25kg.

25

Note – the stockperson looking after these pigs must have been infected with influenza or vaccinated (with the same strain) within first week.


 

               On site nursery and finishing

26

With 2-3 weeks worth of weaners, going off-site, treat the on-farm nursery-finishing operation as described in the infected nursery-finishing section.

Vaccines – pros and cons

 

Influenza viruses are very strain specific.  There can be little or no protection between strains.  Even if the virus carries the same H and N as the vaccine – there may be little or no protection.  This is probably the case between “classical” swine influenza H1N1 viruses – of which there are a number of vaccines and the novel H1N1 2009 strain.

Commercial dead vaccines may reduce/prevent clinical signs – but may not prevent infection or some shedding of the virus from infected pigs.

Once naturally infected with an influenza virus the pigs are immune to that type for life.

Commercial vaccines will only confirm “immunity” for about 6 months.

Antibodies present in colostrum may protect young pigs until 6 weeks of age.

Enhance biosecurity.

Obviously no pigs from the infected site should go to any other site.

There should be no staff movement from infected farm and other farms.

Keep all visitors to a minimum and make arrangements re feed delivery etc.

Summary

 

Close – 2 weeks minimum.

Sell and cull as many animals as possible – reduce population pressure.

Infect – whole herd with sick animals and on-farm autogenous vaccines.

Remove naοve and coughing animals after 2 weeks.

Introduce sentinel animals.

Review sentinel animal health status – after 3 weeks.