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Actinobacillus Pleuropneumonia (App)

(404) The bacterium Actinobacillus pleuropneumoniae was previously called Haemophilus pleuropneumoniae and there are at least twelve different strains, some of which produce no disease and are non pathogenic, but others cause very severe disease. Strains 1, 5, 9, 11 and 12 are highly virulent and strains 3 and 6 are very mild. The organism is carried in the tonsils and respiratory tract and the incubation period is very short, from as little as 12 hours through to three days. It is transmitted by droplet infection between one pig and another. The organism may survive in discharges, serum etc. for up to 5 days. Contact with dead stock is therefore important from biosecurity. It 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 4 months. It is probably airborne for only 5 to 10 metres. Disease is dose dependent i.e. the more bacteria the pig is exposed to the more severe will be the disease. Infection is spread from one pig to another by nose to nose contact. Pigs may be infected with different serotypes simultaneously. PRRS and EP can make the disease worse. In a naïve herd up to 30% 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.

Clinical signs

Acute disease
The organism may affect the pig from weaning through to slaughter but usually the age is from 8 to 16 weeks, once maternal antibody has disappeared. Sudden death is often the only sign with blood and froth discharged from the nose. In the live pig a short cough may be heard with signs of severe breathing difficulties and blueing of the ears. Badly affected pigs are severely depressed. Body temperature is often high. Death is due to a combination of heart failure and the toxins produced by the organisms.

Sub acute disease
This occurs at the same time as the acute disease with pneumonia characterised by abdominal breathing rather than chest breathing because the pleurisy is very painful. This abdominal breathing is used to clinically differentiate between actinobacillus pneumonia where the coughing episodes are short, perhaps one to three coughs at a time, and the prolonged non-productive ones 7 to 10 times, with EP.

Affected pigs may carry the organism for considerable lengths of time and are therefore a potential risk to younger pigs.


This is based on clinical evidence, herd history, post-mortem examinations including slaughter house 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.

Similar diseases

These include enzootic pneumonia, PRRS, SI, and Salmonella choleraesuis pneumonia.


In view of the acute course of the disease it is important to identify clinical cases very early and treat individuals by injection. Affected pigs stop eating or drinking so that 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 and 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

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/tonn
    - Tilmicosin 200 to 400g/tonne for 7 - 15 days

Water medication during the period of risk can be more effective in preventing disease. Treat for 4-7 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 to 400g / tonne has been shown to be very effective used strategically.

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 or water medicate 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.

Management control and prevention

This has two aspects

  1. Exclusion of virulent strains from the herd.
  2. Prevention of clinical disease when virulent strains are present.
Exclusion from the herd

In breeding herds the ideal situation is to have no highly virulent strains present but only mild or avirulent strains which then naturally immunise the herd. A naive herd, (i.e. one that has never been immunised by any natural infection) is a potential time bomb. However in some countries this method of control i.e. a totally naive herd is being advocated. If a virulent strain gets in it will create havoc. Fairly 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. In contrast, natural infection tends to immunise against all serotypes.

In a breeding herd that is free from clinical disease (including absence of characteristic lesions in the lungs) it pays to try to keep virulent strains out. In pig disease areas where herds are close together and the level of infection is high, it may prove impossible to do so on a permanent basis. 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.

The following measures should be adopted:

  • Prevent entry of virulent strains by checking 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.
  • Provide all visitors, including your veterinarian, with a hat, clean coveralls and boots and insist that they wear them.
  • If you have a large valuable herd, install a shower and make all visitors wash their hair, hands and beard if they have one.
  • Check that they 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.
  • Hold incoming breeding pigs in isolation, segregated from your herd for a minimum of three and optimum of six weeks and not only inspect them daily, but check that the source herd is still healthy before you bring them into your herd.
  • Some people advocate testing the pigs in isolation serologically or micro-biologically (i.e. collecting nasal swabs and culturing for the bacterium) but these may be counterproductive because of false positive results and because the laboratory cannot always tell you whether the pigs have virulent or avirulent strains.
  • In grower-finisher units which purchase 25 to 30kg pigs from weaner producers it is difficult to maintain freedom from virulent strains of this organism unless you are purchasing pigs from a single known source or limited number of known sources. The practice of all-in all-out by building or preferably site may also help.
  • The 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 is also likely to result in freedom from this disease.
  • Consider adopting SEW or SDC techniques.
Prevention of clinical disease when virulent strains are present
  • In an infected breeding herd the most likely time to get clinical disease is in pigs over 15kg. If it does occur consider the following:
  • Vaccinate for EP and control PRRS.
  • Consider routine vaccination of sows and/or incoming gilts with App vaccine.
  • New vaccines are coming on the market periodically including a live attenuated genetically modified one which causes no disease but immunises pigs against its bacterial toxins.
  • Operate all-in all-out, at least by room, rather than continuous throughput production.
  • Avoid stress and overcrowding.
  • Avoid rapid temperature fluctuations.
  • Avoid low humidities and low temperatures.
  • Try fogging to decrease the numbers of organisms in the air. 1% Virkon S can be of value.
  • 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 off 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.
In infected grower/finisher units, consider all of the above but also do the following:
  • 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.
  • Practice all-in all-out and not continuous flow.
  • Consider prophylactic medication for a period after entry.
  • Assess the results of vaccination.
Remember that when controlling the environment:
  • 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.

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