Streptococcus suis, the cause of streptococcal meningitis, has been a major problem in some herds especially in weaner and grower pigs and its control has been complicated by the introduction of the immuno-depressant viruses diseases such as PRRS and PMWS.

The infection spreads by aerosol and close contact. It may be transmitted from the sow to the piglet at a very early stage. Lateral spread is also important especially in multi-age houses. The organism colonises the nose and tonsil and from there can penetrate into the bloodstream. Once into the blood it can multiply (septicaemia) and is carried around the body. It can then settle out in joints (arthritis), the brain (meningitis), the heart (causing pericarditis and valve damage), to the abdomen (peritonitis), or to the lungs and cause pneumonia. This is a very typical pattern of bacterial spread via the bloodstream. With recent virus infections such as PRRS virus, which attack the immune system and destroy the cells (macrophages), which eat up the bacteria, there has been an increase of this and other infections such as Haemophilus parasuis (Glässer's disease), which can cause similar clinical signs. The normal disease pattern has changed depending on when the virus attacks. It can be much earlier, as young as 16 days, or later in fattening pigs.

Control of meningitis can be quite difficult but commonly depends on medication with antibiotics, as vaccines are not commercially available in the UK and autogenous vaccines are limited in their protection to just the particular strain on the farm and there may be more than one.

Potencil (penicillin V - Novartis Animal Health) has been the major stand by for many farms to treat and control the disease. It is included in the feed around the time the condition is expected to develop. Fortunately there is little resistance development to penicillin by S. suis and it remains a highly effective treatment of the disease. It is also active against a number of other common pig bacteria associated with septicaemia or pneumonia such as Pasteurella multocida and Actinobacillus pleuropneumoniae.

Table 1. Antimicrobial sensitivity (%) to some major pig pathogens

New information (unpublished data) looking at the sensitivity of these important bacterial pathogens isolated in the UK, showed penicillin V to be highly active against S. suis, P. multocida and H. parasuis, with low minimum inhibitory concentrations (MICs).

Graph 1. Penicillin Sensitivity (%) and MICs against UK field isolates of S. suis, P. multocida and H. parasuis

Other methods of control include treatment of the lactating sows to reduce the transmission of S. suis to the piglets but complete eradication is very difficult on a herd basis, without partial depopulation or a medicated early weaning approach and the sensitivity of the organism should be confirmed first.

Two field trials showed the effect of controlling streptococcal meningitis with Potencil. In the first trial 1000 pigs, 4-10 week of age, were placed on medicated feed for 6 weeks and another 1000 pigs were untreated. Twelve pigs (1.2%) died in the untreated group from meningitis and only 1 in the treated group (0.1%). In the second trial involving 250 pigs in each group aged 4-10 weeks, 14 died (5.6%) in the untreated group and only 1 (0.4%) in the Potencil treated group during the 6 week medication period, a 93% control. Fresh feed was prepared every two weeks.

Table 2. Field trial results with Potencil for the control of streptococcal meningitis

With the introduction of the ZAP (zoonoses action plan) salmonella control scheme it is thought that many of the feeds will be acidified to reduce the pH value below 5 to reduce salmonella colonisation of the gut. A number of enquiries have been made about the stability of Potencil in acidified liquid feed.

Penicillin V was developed for use as an oral product because it was resistant to acid produced in the stomach, unlike penicillin G, which is the normal injected form and used to be in some medicated feed premixes. The stability of penicillin V was tested at different pH levels over a 2 hour period.

Graph 2. Stability of penicillin V at different pH levels over a 2 hour period

There was no degradation at pH 7 and 5 but there was a moderate level at pH 3 (12%) which increased as the pH decreased even further. On this basis, Potencil could be added to dry acidified feed, which was to be mixed and fed as a liquid feed immediately but would not be suitable for use in feed to be fermented down to pH levels of 3, over a prolonged period.

Fortunately the susceptibility to penicillin by a number of major pig pathogenic bacteria remains very high in the UK, which should make Potencil the first line of defence when these organisms threaten their health and performance.

 

References:
Teale, C. (2002) Antimicrobial resistance in porcine bacteria. Pig Journal 49, 52-69

Laperle, A., Nadeau, M. and Cantin, M. (1996) Sensitivity profile of bacteria from bovine, porcine and avian origin against some antibacterial products. Le Medecin Veterinaire du Quebec 26, 1, 26-29

Trigo, E, Mendez-Trigo, A.V. and Simonson, R. (1996) Antimicrobial susceptibility profiles of Haemophilus parasuis, a retrospective study from clinical cases submitted during 1994 and 1995 to a veterinary diagnostic laboratory. Proceedings of the 14th International Pig Veterinary Society Congress Bologna, Italy, p 313

Johnston, P.I., Henry, N. de Boer, R. and Braidwood, J.C. (1992) Phenoxymethyl penicillin potassium as an in-feed medication for pigs with streptococcal meningitis. Veterinary Record 130, 138-139

 

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