(539) Brucellosis in pigs is caused by a bacterium called Brucella suis. There are five different types, called biotypes, which behave in slightly different ways outside the pig.
In most parts of the world where B. suis infects pigs, the most common biotypes causing disease are 1 and 3 with biotype 2 in Europe. Biotype 2 is enzootic in wild hare populations in Northern and Central Europe. Hares transmit it to pigs.
Biotype 4 is enzootic in reindeer and caribou in Siberia, Alaska, and Canada. Pigs are not generally kept where reindeer and caribou are plentiful and type 4 is thought not to be very pathogenic to pigs. Human cases of type 4 infection are not caught from pigs.
Should you be concerned about Brucellosis?
B. suis is not present in the UK or Ireland and if you work in these countries you need not be concerned about it.
It was thought to have disappeared from France and Denmark because no clinical cases had been diagnosed for a number of years. Then over recent years outdoor breeding herds were established which, of course, were exposed to hares. At least one of these in each country caught brucellosis from infected hares. The hares associated with the French (Normandy) outbreak had been recently introduced from Poland by hunters, because the hare population of Northern France had dropped so low.
It is assumed that B. suis is still enzootic in the hare population of Scandinavia and Central Europe but there is insufficient evidence to define the precise area where infected hares exist. It is present in the USA, South America parts of Asia and Australia.
Importance of Brucellosis
Brucella suis is not a highly epizootic infectious organism like, say, TGE or FMD. It spreads slowly between and within herds and you should be able to keep it out of your herd if you take sensible precautions. But it is a serious disease and you must always think of it as such.
If it gets into your herd, it is difficult to eliminate. It causes long term reproductive losses and some biotypes (1 and 3 particularly) also cause a very nasty disease in people. Fortunately, the hare biotype-type 2- is less pathogenic to people. Clinical signs
In a susceptible breeding herd
The earliest sign is usually a few pregnant sows aborting. No other pigs may appear to be affected. If the early abortions are few in number they may be missed particularly in loose-housed sows and in outdoor herds.
The first sign noted then may be a high return to service and vaginal discharges. These returns are 30-50 days after mating if the disease has been introduced to the herd by an infected boar. The females are infected by him at mating. If sows are already pregnant abortions may occur at any stage. The infection arising from contaminated rooting materials or vaginal discharges.
In the boar, B. suis tends to multiply in the testicles and/or the male accessory reproductive glands and is then shed in the semen for prolonged periods. The reproductive tracts of sows and gilts become infected when served by the boar or inseminated artificially. This results in a large proportion of very early abortions. The infection in the sows’ reproductive tracts is not permanent and eventually clears up spontaneously. In contrast, the infection in the boars’ reproductive tract is usually permanent, the damage that it does is irreversible.
It may then be noticed that some of the boars’ testicles are becoming enlarged. A few growing pigs and adults, and a slightly greater number of sucking piglets and weaners start to develop partial or total paralysis in their hind quarters. This is the result of infection and damage to the spine. Some pigs may become lame with swollen joints.
Mortality is likely to be low and the disease may spread slowly but the long term damage to production can be serious.
The combination of abortions, returns to service, vaginal discharges swollen boar testicles, lame pigs and young pigs with posterior paralysis is strongly suggestive but laboratory tests have to be done to make a definitive diagnosis. Best samples to submit are aborted piglets, swabs of vaginal discharges, dead pigs, and blood samples from at least 10 sows, preferably from those which have aborted or returned to service.
The most sensitive and accurate laboratory method is to culture and identify the organism on selective medium which is not difficult. The products of abortion are teeming with organisms. The organism can also be cultured from semen, testicles and accessory organs, lymph nodes, fluid from swollen joints, and in the early stages, from blood.
A variety of serological tests can be done on blood samples, including agglutination and complement fixation tests, ELISAs, and card and plate tests. Both false positive and false negative results occur which is why you need to blood test at least 10 sows and boars, preferably more. Serological tests are unreliable for diagnosis in an individual pig and should be done only as herd tests.
It would be risky to open a dead pig to look for lesions. In the early stages of the disease the organism is spread throughout the pig’s body. Even in the later stages it is fairly widespread. It can infect you through tiny cuts and abrasions on your hands or by being splashed or rubbed into your eye or mouth.
- Treatment with antibiotics is not very effective and generally should not be attempted. Affected pigs should be destroyed.
- If your herd becomes infected the most reliable method of control is to slaughter the herd, clean up the premises and restock with brucella-free pigs. This is also the safest procedure from the pig attendants’ and public’s stand-point and in the long term is usually the least costly. Depending upon the country in which you work, it may mandatory to do so.
- Other approaches include repeated herd blood tests with removal of positive reactors. This may be effective if only a few pigs are infected but is likely to be unsuccessful if many pigs are positive.
Management control and prevention
- The brucella vaccines which have had widespread use for brucellosis in cattle are not effective in pigs. The low incidence of the disease has not made it cost-effective to develop vaccines for pigs and none are available
National or regional control and eradication programmes
- There is a move in a number of countries, including the USA, to gradually eliminate this disease mainly by compulsory slaughter of herds in which the organism is diagnosed combined with various other procedures depending on the particular programme.
- If your herd is free of Brucella suis you should endeavour to keep it free by adopting the methods of biosecurity described in the last section of this chapter.
- The main method of spread is by pig-to-pig contact, through venereal transmission during mating and on-farm do-it-yourself artificial insemination.
- Other materials include the eating or rooting of aborted piglets, dead piglets, aborted afterbirths or materials contaminated by vaginal discharges from aborted sows.
- Exposure of cut or abraded skin to infected materials may also result in transmission.
- Sows shed the organism from the vagina for at least 30 days after aborting, sometimes much longer.
- Suckling sows also shed the organism in milk which then infects their piglets.
- The organism does not spread on wind and rarely on other vectors so the main defence of your herd depends on preventing exposure to infected pigs and the introduction of brucella-free replacement pigs.
Protection of personnel
- Brucellosis in people, also called undulant fever, is a serious long-lasting disease which does not respond well to treatment. Infected people get recurrent attacks of clinical disease over many years. It causes a variety of symptoms including severe headaches, meningitis and bad dreams, severe back-ache, depression and lack of energy and interest, damaged testicles and changes of personality. It is therefore essential that if the organism infects your herd, you take every precaution against people becoming infected.
Main precautions to take
- Wear protective clothing and take it off and wash your hands before eating.
- Wear rubber gloves when handling affected pigs or infected materials.
- Protect your eyes against splashing infected materials into them.
- Do not touch your eyes or put your fingers or any instruments on or in your mouth when working with affected pigs.
- Protect any bare skin on your arms or face that might have cuts and abrasions.
- Get rid of the disease as soon as possible.