Background and history

The bacterium Actinobacillus pleuropneumoniae (App) consists of at least twelve different serotypes, some of which produce no disease but others cause severe disease. Serotypes vary in different countries. Types 1, 5, 9, 11 and 12 are usually highly virulent and strains 3 and 6 are mild. App is carried in the tonsils and upper respiratory tract. It is transmitted short distances by droplet infection through nose to nose contact. It is probably airborne for only 5 to 10 metres.

The organism may affect the pig from weaning through to slaughter but usually the age is from 8 to 16 weeks. The incubation period is very short, as little as 12 hours through to three days. Toxins produce severe damage to the lungs. Disease is dose dependent i.e. the more bacteria the pig is exposed to the more severe will be the disease.

Pigs may be infected with different serotypes simultaneously. Porcine reproductive and respiratory syndrome (PRRS) and enzootic pneumonia (EP) can make the disease worse. In a naïve herd up to 30 percent of animals may be affected. When App attacks the lungs the toxins produced cause severe damage to the tissues which turn blue to black (necrosis) with extensive pleurisy. The chest cavity rapidly fills up with fluid.

The organism may survive in discharges, serum etc. for up to five days. App dies quickly if dried, but it may persist in water for 20 days or more. App can survive in the lungs and tonsils for long periods of at least four months. Contact with dead stock is therefore important from biosecurity.

App is uncommon in sows unless they are naive or disease is triggered by PRRS or flu.

Similar diseases include EP, PRRS, Swine influenza (SI) and salmonella choleraesuis pneumonia.

Clinical signs

Unusual in adult and very young pigs unless a naive herd.

• Sudden death/mortality – only sign is a bloody discharge from the nose.
• Sudden death/mortality – no symptoms and more than one percent of such deaths. Post mortems required.
• Deaths are often caused by a combination of heart failure and toxins.
• A short cough, perhaps one to three coughs at a time – different from the prolonged coughing of EP.
• Severe heavy breathing difficulties.
• Abdominal breathing rather than chest breathing.
  • This abdominal breathing is used to differentiate clinically between App and EP.

• Blueing of the ears.
• Badly affected pigs are:
  • severely depressed;
  • off feed.
    

Diagnosis

• Clinical evidence.
• Herd history.
• Post-mortem examinations including slaughterhouse checks and culture of the organism in the laboratory.
  • The lesions in the lung are very characteristic with large red-blue areas in the upper diaphragmatic lobes with an overlying pleurisy. They can be confused with lesions caused by SI.

• Serology can be used to identify different serotypes but in the absence of disease the interpretation can be difficult because of cross reactions between serotypes.
  

Causes

• Contaminated or carrier incoming pigs.
• Affected pigs may carry asymptomatically for a long period of time and are therefore a potential risk to younger pigs.
• Can be spread mechanically by equipment and visitors.
• Water deprivation.
• Low temperature and low humidity predisposes.
• Stress/movement.
• Nutritional changes.
• Continual production.
• High stocking densities.

Prevention

Management

Management is effective and avoids the need for extensive strategic medication.

The following measures can be adopted:

• Check that the herds which supply you with replacement breeding stock are screened on the basis of herd history, clinical inspections and absence of clinical signs and regular lung examinations at slaughter.
• Avoid introducing pigs from multiple sources.
• Do not mix pigs from herds with the disease and pigs from herds which are free from the disease.
• Provide all visitors, including your veterinarian, with a hat, clean coveralls and boots and insist that they wear them.
• Install a shower and make all visitors wash their hair, hands and beard if they have one.
• Check that visitors have not come direct from another diseased herd.
• Build a loading bay in such a way that when lorries collect pigs the driver does not have to enter your building and you do not have to go on the lorry.
• Avoid loading your pigs onto lorries which already have pigs on board from other farms. All vehicles should be empty and disinfected before arrival.
• Quarantine incoming breeding pigs for a minimum of three and optimum of six weeks and inspect them daily.
• In grower/finisher units which purchase 25 to 30kg pigs from weaner producers purchasing pigs from a limited number of known sources helps to reduce the risk of infection. The practice of all-in all-out by building or preferably site may help.
• Organisation of a multi-site system in which the three-week-old piglets are weaned immediately from the breeding sow site into an all-in all-out nursery before coming to the grower/finisher.
• Consider prophylactic medication for a period after entry.
• Assess the results of vaccination.
• Consider adopting SEW or SDC techniques.
• Vaccinate for EP and control PRRS.
• Consider routine vaccination of sows and/or incoming gilts with App vaccine.
• Watch the market for new vaccines.
• Operate all-in all-out, at least by room, rather than continuous throughout production.
• Avoid stress and overcrowding.
• Increase the levels of vitamin E by 50–100g/tonne.
• Maintain good ventilation and a warm air flow.
• Keep pigs warm, dry and draught free.
• Provide a plentiful supply of easily obtainable water. Temporary water deprivation will trigger disease.
• Consider strategic feed medication in advance of and during the likely time of onset of disease.
• Keep injectable antibiotics in a refrigerator ready for prompt treatment of sick pigs.

Strategic medication

It is important to determine when the onset of the disease is likely to occur, to assess adverse environmental factors and to apply strategic medication just prior to this time.

In-feed medication during the period of risk could include:

• Phenoxymethyl penicillin – 200–400g/tonne
• Chlortetracycline – 500–800g/tonne
• Trimethoprim/sulpha – 300–400g/tonne
• Oxytetracycline – 500–800g/tonne
• Tilmicosin – 200 to 400g/tonne for 7 to 15 days

Water medication during the period of risk can be more effective in preventing disease. Treat for 4 to 7 days. Similar medicines to in-feed medication can be used.

Preventive feed medication is not always effective, probably because of the rapid onset of disease and rapid loss of appetite. However tilmicosin in feed at 200g–400g/tonne has been shown to be effective used strategically.

Exclusion from the herd

Effective vaccines are commercially available in most countries but they only immunise against homologous serotypes (i.e. the serotypes that are incorporated in the vaccine) and not against other serotypes. Natural infection tends to immunise against all serotypes.

In pig disease areas where herds are close together and the level of infection is high, it may prove impossible to exclude the disease from the herd. In more isolated herds it may be possible to maintain freedom from the disease for long periods (although even if extreme measures are adopted, breakdowns may occur, the sources of which are often unknown).

Controlling the environment

• Avoid rapid temperature fluctuations.
• Avoid low humidities and low temperatures.
• Try fogging to decrease the numbers of organisms in the air. One percent Virkon S can be of value.
• Large airborne particles >10µm are retained in nasal passages.
• Particles of 0.5–3µm penetrate deep into lung tissue (bacteria, App and mycoplasma).
• Low temperatures and high humidity produce large droplets that sediment quickly with less exposure.
• High temperatures and low humidity produce small droplets that sediment quickly with less exposure.
• Low temperatures and low humidity produce small droplets that stay airborne – a dangerous environment.

Treatment

In an acute outbreak examine the at-risk group three times daily to identify disease as early as possible. It may be necessary to inject the whole group. The decision to inject is a balance between effect, and risk of more disease due to the stress of handling the pigs.

As affected pigs stop eating or drinking water or feed medication is usually ineffective. App usually has a wide range of antibiotic sensitivity. On the first day inject the pig twice eight hours apart. The following antibiotics are usually effective:

• Amoxycillin.
• Ampicillin.
• Ceftiofur. This is a very rapid acting medicine and gives a good response.
• Enrofloxacin.
• Tiamulin, OTC, LA. This can be used in more chronic cases. Repeat every two days.
• Penicillin.
• Penicillin/streptomycin.