Once disease affects a pig herd the impact on the economics of pig production in terms of the cost of control and decreased productivity can be enormous. The first priority must therefore always be to try to prevent the occurrence of disease.
Thus, many of the management procedures considered here are aimed at disease prevention or at mitigating the effects of those diseases that cannot be prevented. With skilled management, combined with well-designed housing and sound nutrition, an overall strategy to minimise the possibility of disease attack can be formulated.
At the same time a basic knowledge of the main diseases which may affect a pig herd is necessary so that a producer can diagnose the condition and implement control measures as quickly as possible.
This is of particular significance under tropical conditions where the regular services of a veterinarian are often not available. The major disease problems are parasites, infectious disease and a few non-specific diseases. Nutritional deficiency conditions are also common causes of health problems.
Parasites are defined as organisms which live on and obtain feed from the body of another, known as the host. They may live on the exterior of the pig when they are known as external parasites, or within the internal tissues and organs when they are known as internal parasites.
Parasite will seldom result in the death of the host except in the case of massive infestations or if the host is also stressed in other ways.
1a) External parasites
These mainly cause irritation to the skin surface, often leading to wounds and an increased susceptibility to other infections. The most common external parasites are mange-mites, ticks, lice, fleas and flies.
Mites, which are scarcely visible to the naked eyes, spend their entire lifecycle under the skin of the pig, but they can survive off the host for as long as eight days. The most common species is sarcoptes scabiei which cause sarcoptic mange.
First signs of infection are a crusty, dry-looking skin around the eyes, ears and snout. The mites then spread and multiply over the body, and their burrowing causes the skin to become inflamed and swollen. The pig will be seen to be constantly rubbing itself and performance is depressed.
Control is best affected by regular treatment, either dipping or spraying with an anti-mange medication, including spraying of pens. Chronically infected animals should be culled. There are also some recent systemic drugs on the market which are very effective against the mite.
Ticks are only a problem in scavenging or more extensive systems of pig production. There are a number of different species which suck blood and can transmit serious disease (e.g. Babesiosis or redwater). They generally require more than one host to complete their life cycle.
Ticks are easily controlled by spraying or dipping with suitable acaricides.
1aiii) Lice and fleas
Both lice and fleas can become a problem in dirty and unhygienic conditions, as they live on the skin surface, suck blood and cause irritation. Spraying of the pigs and pig quarters with suitable insecticides are effective ways of controlling the pests. In the case of lice, particular attention should be paid to the ears.
Flies have a major nuisance-value around pigs as they cause annoyance, can bite, and carry infectious diseases. They are always attracted to any fresh abrasion or wound on the animal.
Control measures should involve spraying of insecticides on suitable fly-breeding areas, e.g. manure heaps, refuse areas and ponds, pig-buildings and the pigs. Baits which attract the flies and are poisonous to them but not the pigs can also be effective.
1b) Internal parasites
1bi) Round worms
These are a particular hazard when pigs are free-ranging or not kept on concrete floors. The large roundworm (Ascaris lumbricoides) is very common and can cause a lot of damage in pig herds.
Adults live in the small intestine and can grow up to 300 mm long a 6mm thick. The female is capable of laying thousand of eggs per day, which pass out in the dung and become infective, if ingested by other pigs, after 21 days.
These eggs are extremely resistant and can remain infective for many years. As part of the life-cycle, eggs hatch out in the pig after ingestion and the larva migrate through the liver and lung. Irritation in the lungs causes coughing and ill thrift, particularly in younger pigs.
Damage is also done to the liver which renders it liable for condemnation at slaughter (‘milk-spot liver’). Moreover, if infection is heavy the adult worms can partly obstruct the small intestine, causing weakness and loss of weight by the pigs.
Contaminated feed and water are the usual source of infection with internal parasites. Control can be effected by breaking the life-cycle, which means regularly moving ranges pigs on the fresh ground and frequent cleaning and removal of faeces in housed pigs.
At the same time, unless there is good evidence that there is no worm infection in the herb; breeding pigs should be routinely dosed with broad spectrum anthelminthics and young stock dosed soon after weaning.
The common tapeworm is Taenia solium. The pig is its intermediate host and the adult worm lives in man. Pigs become infected by picking up eggs from human faeces and the larvae then encysted in the pig’s muscle, particularly in the region of the heart and tongue.
If the pig meat is then eaten by man, the larvae hatch out and the cycle is completed. As a consequence, bodies which are affected (measly pork) are condemned at slaughter. By preventing pigs having access to human faeces, the parasites can be eliminated.
In some countries live pigs are checked at the market place by trusted experts for the presence of tapeworm’s cysts in the tongue. The result of the examination influence the price paid to the producer.
2) Infectious diseases
The following diseases are notable in most countries.
2a) African swine fever
This is a highly contagious virus disease which in the acute form can cause 100 per cent mortality. Typical symptoms are loss of appetite, pigs huddling together, small purplish blotches on the skin, incoordination and laboured breathing.
In Africa, both bush pigs and warthogs are carriers of the virus but are immune to the disease, and it is therefore very important to prevent direct contact between domestic pigs and wild species.
This contact can be prevented by double penning and the control of animal movements.
Moreover a soft tick (ornithodoros moubata) which infests the warthog is a biological carrier. Otherwise infection occurs by contact with other sick pigs, or through contaminated feed or water.
There is no effective vaccine or treatment an infected pig should be isolated from healthy ones. Although the disease originated in East Africa, it is gradually spreading west through Africa.
2b) Foot-and-mouth disease
Regarded as the most contagious of all known viral diseases, infection causes blisters on the feet, snout, and udder and in the mouth and throat. It is very painful to the pig, which cannot eat and often has to be destroyed.
The disease is endemic in parts of Africa and the virus is carried by the buffalo. Infection can occur by feeding infected bones or cooked meat.
There is no cure. If an outbreak occurs in adjacent area, pigs can be vaccinated, but as there are many different strains of the virus it is important to ensure that vaccination is against the right virus.
Other Infectious Diseases
This disease, which is caused by a bacterium, is also known as contagious abortion. Brucellosis can result in temporary or permanent sterility in females. Abortion is the most common symptom and can occur at any stage of gestation, depending upon the time of exposure to infection with the bacterium. In boars, testicles may become inflamed and permanent sterility may result.
The disease is transmitted at mating or by contaminated feed or water. There is no treatment and infected animals should be culled, particularly as brucellosis is transmissible to humans, and the risks of transmission are relatively high under some traditional systems of pig management. Brucellosis appears to be widespread in pig herds in south East Asia and the pacific Islands.
This is caused by organisms known as coccidia, of which are 13 known infective species in swine throughout the world. They cause damage to the intestinal wall, and are believed to be an increasing cause of diarrhea in piglets, particularly in confined housing. Piglets show a grey-green diarrhea, lose weight and rapidly become dehydrated.
Coccidiosis is spread by contaminated faeces and thus good management and regular cleaning of buildings will prevent the disease. Drugs, known as coccidiostats, are available for prophylaxis and treatment.
Salmonellosis is another enteric disease, caused by the salmonella spp. of bacteria. Pigs generally are affected around two months of age, and become gaunt, with a high temperature and a foul-smelling diarrhea. There are usually some deaths in a group of infected pigs.
An outbreak is often triggered- off by a stress condition, particularly heavy worm-infestation. The disease can therefore be prevented by good management and sanitation. Antibiotics and sulpha drugs will aid in the control of the disease.
SMEDI is an acronym for reproductive failure conditions involving stillbirth (S), mummification (M), embryo death (ED) and infertility (I). It is caused by viruses, mainly porcine parvovirus and the enteroviruses.
The symptoms will vary according to when the sow or gilt becomes infected. If infection occurs during the oestrous cycle and at service, the sow will show a regular or irregular return to oestrus, or if only some embryo die she will produce a very small litter.
If infection occurs after 35 days of pregnancy, the foetus die and dry up and are presented at farrowing as “mummified” foetus. The condition can cause a serious decrease in sow productivity within a herd.
There is no treatment but effective preventative vaccination programmes are now available. If vaccines cannot be obtained, all gilts and new animals entering the herd should be given access to farrowing house waste 30 days before breeding. This exposes them to the viruses and stimulates immunity.
5. Swine dysentery
This disease is caused by a large spirochaete, and is manifested by a severe diarrhea producing reddish – black faeces. Infected pigs rapidly lose weight. The disease is spread by infected dung and can largely be controlled by good hygiene. There are effective antibiotic medications on the market.
6. Swine influenza
Swine influenza is a highly contagious respiratory disease caused by an influenza virus. It is normally triggered off by a stress, particularly rapid changes in temperature. Although mortality is low, the disease has important economic consequences due to stunting and reduced liveweight gains.
The first sign of the disease is normally a cough, with a high temperature and loss of appetite. The disease spreads rapidly, breathing becomes jerky and the hair coat develops a rough appearance. Secondary infection with bacteria may complicate the condition.
There is no treatment or preventive vaccine available. Infection can be prevented by good management and the avoidance of stress.
7. Swine pox
Swine pox is a virus disease, and is transmitted either by direct contact or by ecto -parasites such as lice. Small red areas (about 1.25cm in diameter) appear on the skin around the head, ears and ventral surface which eventually form scabs.
There is no treatment for swine pox, but although unsightly it rarely causes serious loss and clears up after a short time.
8. Transmissible gastroenteritis (TGE)
TGE is a virus disease which causes acute diarrhea; vomiting and early death in young piglets. It also affects older pigs causing diarrhea and vomiting, but rarely death.
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There is no treatment. Infected pigs can be isolated, or killed and buried. After infection, the whole herd is likely to be immune.
Abscesses can occur as the result of any irritation, inflammation or wound which allows access to bacteria, normally strains of Staphylococcus or Streptococcus. The body of the pig reacts to the invasion of the bacteria, and a pocket of pus is walled off from the body.
Abscesses are seen as swellings or lumps, often hot to touch and they will in time develop a soft area which can be lanced and drained. They may be superficial or they may form deep within the body, where they can cause lameness, interfere with breathing or swallowing, or may not be discovered until slaughter.
As abscesses are painful and can markedly depress performance and reduce carcass value, every effort should be made to minimise the possible causes in a piggery. Preventative measures include the removal of any sharp or rough object from pig pens, ensuring the floors are not too rough, especially for baby pigs, making sure that injection equipment is sterilized and providing overall good sanitation. Abscesses can be treated with antibiotics, but this is not always effective.
2. Gastric ulcers
Ulcers tend to occur as a response to stress in pigs of all ages, and are particularly prevalent in genetic strains bred for fast growth and a thin covering of back fat. The nature of the ration is also important with a higher incidence of ulcers occurring on finely ground, highly -energy concentrate diets.
There may be no specific external symptoms, unless haemorrhaging occurs. Otherwise pigs show lack of appetite, will huddle together and become thin. Mortality varies according to the extent of the ulceration. There is no specific treatment apart from reducing stress. Changes in the ration, involving an increase in fibre levels is often useful in ameliorating the condition.