Part 1 – Basic Principles

Introduction

When compared to large commercial pig keeping operations, the small pig population presents different health challenges. The smaller population can exist as part of a mixed animal small holding, as a part-time venture, as a hobby farm or, in some cases, as a high value rare breed or pedigree population. Increasingly, pet pigs have also become more common.

Smaller herds may not suffer the same major disease issues seen in the larger commercial sector but there is greater focus on the individual pig. All pigs are susceptible to the same range of diseases and disease conditions in the individual take on a higher level of importance.

As with all species, vaccination forms an important part of the overall health management of the pig, which is often overlooked in small populations.

What is Vaccination?

When animals are exposed to infection, provided they recover, they will develop an immunity which will protect them against future repeated challenge to that infectious organism – be it bacterial, viral or other types of microbes.

The aim of vaccination is to mimic the challenge by exposing the animal to a controlled dose of an adapted form of the specific organism prior to the risk of full challenge, thus stimulating natural immunity. In some cases, this may be effectively life-long but others may require booster doses (much like the use of vaccines in human beings).

Vaccines are initially prepared from field strains of infectious agents known to cause disease in pigs. The organism may be included in the vaccine in a live form – altered to render it less harmful to the pig – or be inactivated chemically. Some vaccines either include or are only formed of the toxin (poison) typically produced by harmful strains of the organism. The precise nature of the vaccine will determine the strength and duration of immunity that will ensue and the dose regime required to be effective.

However, certain features are common to all vaccines:

1. They are specific to the organism or organism included e.g. E. coli vaccines only provide protection against that organism; they are not protective against other causes of diarrhoea.
   
   
2. They do not treat the disease concerned and they do not prevent infection but they prevent future disease.
   
   
3. They take time to work – typically a few weeks and thus must be administered in a timely fashion.

Within the pig population vaccines can be targeted in a number of ways:

1. To provide protection against disease in the animal to which the vaccine is given, e.g. enzootic pneumonia vaccine.
   
   
2. To provide protection to the unborn litter of a breeding animal, e.g. porcine parvovirus vaccine.
   
   
3. To stimulate immunity in the dam that is passed on to piglets (via colostrum) to protect them only, e.g. E. coli vaccines.
   
   
4. A combination of effects, e.g. Erysipelas vaccines.

In the majority of cases in pigs, vaccine is administered by individual injection although there are an increasing range of vaccines becoming available, which now include a live oral vaccine against ileitis (Lawsonia infection).

Clinical Disease Condition

1. Porcine parvovirus (PPV)

Figure 1. Sequential mummification due to porcine parvovirus

Figure 2. Engorgement of the vulva and skin discolouration seen with PRRS infection

Figure 3. Late gestation mummification seen with PRRS infection

PPV is a viral disease, which only affects the pregnant animal by damaging the unborn litter. As such, it can produce:

• Returns to service – typically at more than three weeks post-service (due to embryonic deaths)
• Small litters (including those less than four pigs – again due to embryonic deaths)
• Mummification – due to foetal death
• Stillborn pigs – due to late foetal death or slow farrowings where high numbers of mummified pigs are present
• Delayed farrowing – especially with small litters

NB. PPV does not cause abortions but is the most common cause of SMEDI syndrome.

2. Porcine reproductive respiratory syndrome (PRRS/Blue Ear)

A viral disease that can infect and affect all ages of pigs. In young piglets the principle signs are scour, weakness and high mortality, with many pigs born weak and underdeveloped. Haemorrhages and swelling around the eyes are occasionally seen.

In growing pigs, respiratory disease is the principle sign but PRRS virus depresses lung immunity and therefore often occurs in conjunction with other respiratory agents and acts as a trigger for complex disease. It is a major component of Porcine Respiratory Disease Complex (PRDC). Rarely, blue ears will be seen.

In adults, the virus can have both a direct effect on the sow or boar producing depression, inappetance, vomiting, skin discolouration (especially of the extremities), agalactia etc. However, it also has significant effects on breeding with abortions, premature farrowings, failure to farrow (not in pig sows), stillbirths and late mummification.

3. Porcine circovirus-associated disease (PCVAD)

This viral disease only affects growing pigs although the age affected is highly variable – as young as five to six weeks up to 20 weeks, but in all cases mortality rates are high.

Various manifestations are seen:

1. Post weaning Multisystemic Wasting Disease (PMWS) – one of the initial presenting signs in which rapid extreme loss of condition in pigs typically seven to 12 weeks of age is accompanied by enlarged superficial lymph nodes (esp. superficial inguinal LN). Profuse watery scour and respiratory distress may accompany the condition. Mortality rates are high.

Figure 4. Wasting typical of PMWS

Figure 5. PDNS skin haemorrhage

Figure 6. Outbreak of acute PCVAD

Figure 7. Lung consolidation in the cadiac lobe typical of enzootic pneumonia

1. Porcine Dermatitis Nephropathy Syndrome (PDNS). Often occurring later than PMWS and as an immune-mediated condition, may be viewed as a ‘recovery disease’, sudden onset haemorrhage of the skin is the most noticeable feature. Due to protein loss from nephritis, oedema of the legs is common. Again, mortality is high in affected pigs.
   
   
2. Non-specific PCVAD – usually a respiratory or enteric-based disease often complicated with bacteria. It can present as an acute systemic disease with high temperature, depression and anorexia, coughing and severe dyspnoea, along with scour that can range from profuse and watery to mild looseness. Discolouration of extremities is seen as in septicaemias and the superimposition of secondary infections (such as streptococci and Pasteuella,) will distort and exacerbate signs in individuals. Mortality is generally less extreme than with PMWS and PDNS but can still be significant.
   
   
3. Peracute PCVAD causing sudden death due to massive accumulation of fluid in lungs
   
   
4. PCV2 is also capable of causing reproductive failure in naive adults – presenting variably as returns to service, abortion, mummification and stillbirths. However, experience in the UK suggests that this presentation is extremely rare.

4. Mycoplasma hyopneumoniae

This organism is the cause of enzootic pneumonia (SEP) of pigs – a widespread condition producing respiratory disease in growers. It is a component of the Porcine Respiratory Disease Complex (PRDC) and tends to be more of a problem in larger populations.

Coughing and laboured breathing are the principle signs with slowed and uneven growth typical manifestations. Death is rare in uncomplicated cases but secondary infection with other agents can cause significant mortality.

SEP is routinely monitored in slaughter pigs.

5. E. coli enteritis

Figure 8. Typical neonatal E. coli diarrhoea

Figure 9. Haemorrhagic intestine seen with Clostridium perfringens infection

Whilst E. coli infections can affect young piglets from birth up to around eight weeks of age, it is the newborn piglet that is especially vulnerable and is relevant to prevention by vaccination.

Diarrhoea (scour) in the first three days of life is severe and watery and causes rapid dehydration and death. Death is often worse in litters from gilts but potentially any litter can be affected. Hygiene in the farrowing area is critically important.

6. Clostridial enteritis

Often occurring in conjunction with E. coli and particularly a problem in sows farrowing on soil that is contaminated.

Piglets can scour from a few hours of age up to one week, although depending on the strain involved, haemorrhage can occur into the gut such that the piglets die before they have a chance to show diarrhoea. Any scour in baby piglets with obvious bloody content would suggest Clostridial involvement.

7. Erysipelas

Erysipelas is a bacterial disease to which all pigs are particularly vulnerable, with the causative organism widely found in the environment and carried in the gut of many species of wild animals including rodents and birds.

Figure 10. Diamond lesions on the back of growing pigs are typical of erysipelas

Figure 11. Skin sloughing following Erysipelas infection

Figure 12. Crippling arthritis due to chronic erysipelas

Figure 13. Snout distortion typical of progressive atrophic rhinitis.

In adults, it can present with high temperature (42°C or more), depression and lethargy sometimes with characteristics ‘diamonds’ on the back and sides. Pregnant animals can return to service or abort. Affected boars are sterile for up to eight weeks.

In growing pigs, the disease can vary in severity from peracute – causing sudden death due to septicaemia – to acute illness (as in sows) with diamond lesions on the skin. Mild cases may show skin lesions without illness.

In the longer term, affected pigs may be crippled with arthritis, have necrosis of the skin or be found dead due to lesions growing on the heart valves (endocarditis).

8. Atrophic rhinitis

Infection of young piglets (under eight weeks of age) with Pasturella multocida type D can damage the nasal tissues of the growing pig, producing distortion of the snout and loss of the filter effect of the nose. Growth is severely impeded and secondary bacterial disease of the lower airways is common.

High levels of sneezing will occur in affected pigs and severely affected animals will have nosebleeds (epistaxis).

Vaccines available

Table 1 (below) provides a list of vaccines currently available for disease control in pigs (2010) with a note of their relevance to the smaller pig producer.

Key to table

XXX: High risk diseases for which all pig populations should be vaccinated if relevant type/age of animals are present.
XX: Can be significant diseases in smaller populations and vaccine given where there is evidence of risk, previous experience or for peace of mind.
X: Rarely significant in small populations, especially if they are stable groups.

In addition to vaccines available for prevention of disease, a product was made available in 2009 that is used to immunologically castrate male pigs, temporarily, close to slaughter weight. It is potentially useful to the smaller specialist niche market producer who is not constrained by the embargo in any form of castration imposed by Quality Assurance Standards appropriate to large commercial farms.

This vaccine removes the need to castrate piglets for meat production, particularly in unusual breeds, for private butcher sales and farmers’ markets. Two doses are required in growing pigs with the second dose given six weeks prior to slaughter.

Further Reading

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Find out more information on the diseases mentioned in this article by clicking here.