Background and history

Streptococci are common organisms in all animals including people. They are broadly but not entirely species specific. The main species is Streptococcus suis which is widespread in pig populations of Europe, the Americas and Australasia and probably occurs wherever pig farming is carried out. It is associated with a variety of conditions including meningitis, septicaemia (infection of the blood), polyserisitis (inflammation of the lining of the abdominal and chest cavities), arthritis, endocarditis (infection of the heart) 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.

The situation is not as simple as it may first appear. S. suis is sub-divided into at least thirty-four serotypes. They vary in their pathogenicity and the diseases 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. Type 2 occasionally also causes septicaemia and meningitis in people, mainly in people handling pigs or pig meat products. Fortunately human cases are rare in the West but a little more common in parts of SE Asia. There is at least one report of an isolation of type 14 from a human brain.

Different types predominate in different countries with type 2 among the commonest in most countries and the type most often associated with disease. (One exception is Denmark where type 7 is the most common). In the UK type 2 is the main cause of serious acute meningitis, along with polyserisitis and arthritis in weaned and growing pigs and it is rarely associated with pneumonia. Type 1 occurs fairly commonly in most countries and causes sporadic arthritis and occasionally meningitis in sucking piglets usually around one to two weeks of age but sometimes up to six weeks. It is a relatively unimportant condition. There was a flare up of types 9 and 14 in the UK in 1998-9. Both caused predominantly arthritis and some meningitis in young piglets but they produced slightly different pictures. When it first appeared in a herd type 9 tended to cause acute very painful arthritis in several joints in both sucking and recently weaned pigs in up to 25% of litters. Affected piglets fell over. About 10% developed meningitis. Penicillin (usually potencil) fed to lactating sows and weaners controlled the disease which gradually disappeared over a period of up to a year. Type 12 caused massively swollen hock joints in 10 day old pigs. Penicillin was again used to control it. Some farmers put it in peat in the creep area and, if the creep was covered, removed the cover. Type 12 also disappeared from herds and is now rarely diagnosed. The syndrome that is important and worrying to the pig farmer is persistent endemic meningitis caused by type 2.

S. suis 2 is spread from one pig to another by direct nose to nose contact. It can also spread within a herd by indirect contact and in confined space by aerosol infection. 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 in the tonsil as part of the normal flora. S. suis is not spread by AI or hysterectomy. The most likely source of entry into the farm is the purchase of carrier boars or gilts. There is little documented evidence to suggest that the human will transmit disease from pig farm to pig farm. 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.

An interesting research finding is that S. suis type 2 is carried from the base of the tonsil to the brain, joints and serosal surfaces inside migrating white blood cells called monocytes (analogous to the "Trojan horse"). Pathogenic strains can survive and multiply in these cells whereas non-pathogenic strains cannot. 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.

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.

Clinical signs

Weaners and 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 and piglets

• Rare

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.

Similar diseases

Similar nervous signs may occur in aujeszky's disease, glässers disease or salt poisoning (water deprivation).

Causes

• 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.

Prevention

• If your herd is free from this disease, try to keep it free.
• Check out your sources of replacement stock before purchase.
• Do not purchase pigs from herds with clinical cases of meningitis.

Treatment

• This must be carried out as soon as disease is recognised.
• Remove the affected pig from the group to a hospital pen. Meningitis is extremely painful and the recovery rate is increased substantially through good nursing.
• Provide warmth and bedding and trickle water into the pigs mouth from a hosepipe every 4 to 6 hours. Alternatively, water can be given by inserting a narrow hosepipe gently into the pigs rectum or using a flutter valve. (See chapter 15).
• Give intra-muscular injections of penicillin 2 to 3 times daily for the first 24 hours.
• Use a quick acting penicillin for the first 24 hours followed by long-acting penicillin. Time is of the essence with this disease. Trimethoprim/sulpha would be an alternative medicine to use.
• Strategic medication - This is a method to adopt on farms where disease levels remain high. The following options are available:
• Identify the onset of disease and apply strategic medication 2 to 3 days before that time.
• Strategic medication can be applied in the drinking water using phenoxymethyl penicillin, tetracyclines, synthetic penicillin particularly amoxycillin, or trimethoprim/sulpha.
• In-feed medicate continuously from day of weaning through to six weeks post-weaning. Phenoxymethyl penicillin at a level of 300g/tonne is the medicine of choice. TMS could also be used.
• Inject all pigs with long-acting penicillin at weaning time.
• Assess the response to injecting pigs with long-acting penicillin five days before weaning.