Streptococci are common organisms in all animals. They are broadly but not entirely species specific. The main species in pigs is Streptococcus suis which is widespread in pig populations and probably occurs wherever pig farming is carried out. It is associated with a variety of conditions including meningitis, septicaemia, polyserisitis, arthritis, endocarditis and pneumonia. It has also been isolated from cases of rhinitis and abortion. The pattern and relative importance of the different syndromes vary in different countries.
S. suis is sub-divided into at least thirty-four serotypes. They vary in their pathogenicity and the clinical signs they cause, both between and within types. Some types appear to be non-pathogenic and have been isolated mainly from healthy pigs, some are mainly associated with lung lesions, and some have been isolated from other animal species as well as pigs. Some types, mainly 2, can occasionally cause meningitis in people as well as pigs. Fortunately human cases are rare.
The syndrome that is important and worrying to the pig farmer is persistent endemic meningitis caused by type 2.
Clinically healthy pigs can carry the organism in their tonsils for many months and a carrier state exists in some sows. Once a serotype has entered a herd no techniques are yet available to remove it and it becomes established as part of the normal flora. S. suis is quickly killed by disinfectants in common use on farms, including phenolic disinfectants and chlorine and iodine based ones. Detergents will also kill the organism in thirty minutes. ‘Savlon ‘ is particularly effective. Outside the pig, in very cold and freezing conditions, it may survive for 15 weeks or more but at normal room temperatures it dies within one to two weeks. It survives long periods in rotting carcasses.
The sow passes on antibody through colostrum to the sucking pig and the disease is therefore uncommon in this group of animals unless it is introduced into the herd for the first time. It is much more common in the immediate post-weaning period often starting 2 to 3 weeks after weaning and continuing through to approximately 16 weeks of age. In flat decks or nurseries almost 100% of pigs become carriers within three weeks.
There are also strains of low pathogenicity which may be activated by PRRS virus infection. PRRS may also raise the incidence of meningitis caused by pathogenic strains when it first enters a herd. Although PRRS alone does not affect the brain, it has been shown experimentally that many more pigs are affected with meningitis when they are infected with both S. suis type 2 and PRRS viruses than when they are infected with S. suis alone. S. suis type 14 which was first isolated from a case of human meningitis is emerging as a new disease in the UK with the appearance of acute severe outbreaks of arthritis in both sucking and weaned pigs.
Species of streptococci other than S. suis may sometimes cause disease in pigs. For example, Streptococcus equisimilis causes sporadic cases of septicaemia and arthritis in sucking pigs, infection of the heart valves in growing pigs and ascending infection of the womb in sows. In the USA Streptococcus porcinus causes throat abscesses and septicaemia and is sometimes isolated from pneumonia. However, cases of streptococcal throat abscesses have become rare in modern systems of pig housing.
Symptoms
Weaners & Growers
Cases of acute type 2 meningitis:
- The pig may just be found dead.
- In very early stages of meningitis the pig is laid on its belly, hair standing on end and shivering.
- Within two to three hours there are lateral jerky movements of the eye (nystagmus).
- The animal then lies on its side paddling and frothing at the mouth. Salivation
- The organism invades the blood stream and is carried around the body where it may cause arthritis and pneumonia. Pigs squeal with pain and refuse to stand.
- Abscesses.
- Fits and convulsions.
- Head on one side.
Type 1 occurs fairly commonly in most countries and causes:
- Sporadic arthritis.
Occasionally meningitis is seen in sucking piglets usually around one to two weeks of age but sometimes up to six weeks. It is a relatively unimportant condition.
Sows & Piglets
- Rare
Causes / Contributing factors
- S. suis is spread from one pig to another by direct nose to nose contact.
- Carrier boars or gilts.
- It can also spread within a herd by indirect contact.
- In confined space by aerosol infection.
If you have the disease endemic in your herd the incidence increases with :-
- High stocking density in flat decks.
- Continuous production systems which perpetuate infection.
- Concurrent PRRS infections.
- Mixing of pigs post-weaning.
- Too small cubic capacity air space per pig. Provide at least 0.8 cu.m. per pig at weaning.
- Poor ventilation and high humidity.
- High dust levels.
- Stress.
- Damp pens.
- High slurry levels under perforated metal floors.
- Weighing pigs and associated stress.
- Tattooing, ear notching and extra stress at weaning.
- Changes in nutritional status at critical times.
- Low vitamin E in the diet. Assess the response to adding 50-100iu/kg.
Diagnosis
A history of the presence of recurring meningitis in weaned pigs is highly suggestive and is confirmed by the isolation of the organism from the brain and its specific identification, which not all diagnostic laboratories are capable of.
Because of the existence of strains that are non-pathogenic or only mildly pathogenic, the isolation of S. suis type 2 from the tonsils of a pig is difficult to interpret. Isolation from the brain of a pig showing signs of meningitis is more conclusive.
The disease must be differentiated from aujeszky’s disease, glassers disease or salt poisoning (water deprivation) which all produce nervous signs.