23 Nov 2015
Ian Roper
Job Title
Figure 1. Lymphoma cytology. Lymph node fine-needle aspirate of a dog with typically high-grade/large cell lymphoma.
This article looks at commonly encountered infectious issues found in pigs in the smallholder environment and discusses some key considerations in treatment.
Diagnostics are not discussed in detail, but the importance of the identification of involved pathogens must be seen as a keystone to effective treatment. Furthermore, the importance of preventive medicine should not be underestimated for (or by) the smallholder, with hygiene, biosecurity and vaccinations particularly in mind.
When considering antimicrobials, less advanced agents may be more appropriate than fluoroquinolones or later generation cephalosporins, in line with the Responsible Use of Medicines in Agriculture Alliance (RUMA) guidelines. Obtaining cultures for sensitivity testing is a core principle of this.
Practicalities might necessitate long-acting injections or oral medication. Medicating the drinking water is usually quite straightforward, but often means the whole group will be treated (which could be desirable when a high proportion of the group is affected). Unfortunately, water and feed intakes are reduced in disease, and markedly varied between individuals, giving chaotic plasma drug levels (del Castillo et al, 2006). It is therefore appropriate to inject the clinically affected pigs and occasionally initiate oral treatment with a compatible product.
There is a compelling argument to omit antibiosis in viral disease. This is well and good if the condition is uncomplicated. Where there is acute disease and a known risk, simple viral disease may be diagnosed.
To omit the antibiotic component also requires confidence in the environment that secondary bacterial pathogens will not become involved later. The client’s full trust would also definitely be needed in that decision. Close monitoring and effective follow-up of case progression are imperative.
In general, the vet-farmer relationship and a team approach are vital for implementing management changes and progressing the health and productivity of the herd.
Supportive therapy would be indicated in some form for any condition and may involve NSAIDs, fluid and electrolytes (especially in cases of diarrhoea). There are practical obstacles to intravenous fluid therapy and fluids cannot be loaded orally as with ruminants. However, intraosseous fluid therapy or syringing into the rectum is possible. Neonates can also be stomach-tubed, using soft plastic tubing approximately 4mm diameter.
Licensed NSAIDs include the parenteral meloxicam, ketoprofen, flunixin, tolfenamic acid and the oral paracetamol and sodium salicylate. It would be usual to include these when the pigs are pyrexic. The antipyretic effects could help maintain feed intakes and improve recovery. Isolation in a hospital pen is always advisable for close monitoring, reduction of disease transmission and because pigs may instinctively attack a weak member of the group.
Very few small pig farms or pet pig enclosures are built with the vet in mind. Lack of restraining facilities can make examination and treatment a real challenge. However even a makeshift pig board can help trap a pig in a corner of a yard or box. It is frequently dark too, including during daytime when inside unlit arks, making a head torch a valuable asset.
Commercially available injection systems can allow intramuscular injections of up to 20ml rapidly from a distance of around five feet. Sometimes, this can even be achieved over a fence. It is particularly useful for administering sedative to allow examination.
It is sometimes easier said than done, but if a pig snare can be placed then almost any procedure can be carried out, except perhaps auscultation, since snaring normally elicits a loud and continual squeal. The pig is often distressed, but not harmed if the snare is used properly so this should only be used when necessary and by a fully competent operator. The process can be upsetting for owners though.
Purpose-made wire devices are preferable, but baling twine or thin rope can be used. The noose is placed in the mouth and tightened over the snout and, crucially, at the caudal extent of the mouth.
If you can get near the pig to examine and treat, but it will not stay still enough for injections, then extension tubing can be connected between needle and syringe. The pig can be jabbed, with the drug being pushed in by the practitioner following at the length of the tubing. The added advantage is that if the pig breaks away, the needle can be pulled from the animal and not left in situ.
Pyrexia with no other specific signs is common and further work-up as discussed previously should be encouraged in these cases. Since infection of some description would be the most likely reason for pyrexia, antibiotics may have a role, but the choice is difficult.
In cases of gastrointestinal infection, diarrhoea is likely to be the main presenting sign, but is not always apparent.
The age group affected is important in considering potential diagnoses. When treating gastrointestinal infections, it is important to bear in mind the host’s immunity. Disrupting normal flora has the potential to interfere with the animal’s recovery, so antibiosis may not be required for moderate infections without systemic involvement, but supportive therapy is key.
Some indications for including antibiosis are:
Confirming a diagnosis of swine dysentery (Brachyspira hyodysenteriae) is really important for the pig industry as a whole, since its presence on smallholdings represents a significant risk to commercial producers.
The national prevalence in relation to geography is vital information in the fight to reduce and eliminate the disease.
A broad diagnosis of respiratory disease may be straightforward, but there are few hints and no pathognomonic signs as to primary cause on the basis of clinical exam.
Determining the pathogen responsible may be useful for future control strategies, including vaccination, which requires definitive diagnosis through laboratory identification. Aside from postmortem examination, nasal swabs may be of benefit, but paired serology would be definitive. In the short term, it is more important to administer treatment likely to be effective against any of the differential diagnoses.
Mycoplasma (M hyopneumoniae and M hyorhinis) is often involved and should be ruled out if the antibiotic selected does not include such organisms in its spectrum of activity. Other commonly implicated pathogens include porcine reproductive and respiratory syndrome (PRRS) virus; swine influenza; respiratory coronavirus; Glässer’s (Haemophilus parasuis); and App (Actinobacillus pleuropneumoniae).
“Joint-ill” in piglets results from environmental bacteria gaining access to the bloodstream through the umbilicus; teeth-clipping injuries; tail-docking stumps and skin abrasions (especially over the carpi when on rough flooring).
Lincomycin or amoxicillin are usually effective, but may need to be an extended course. The discomfort of this condition should not be underestimated and therefore analgesics are of real value.
Lameness in growing pigs is often the result of septic arthritis. In severe cases this can present as recumbency rather than lameness, although palpation of the affected joints would normally reveal fluid swelling and elicit a pain response. Sterile forms of arthritis do occur and aseptic arthrocentesis would help differentiate.
Gram-positives are the most likely to be present, but given the other possibilities, lincomycin is the antibiotic of choice. Tiamulin and macrolides are likely to be effective too.
“Bush-foot” is a chronic, potentially severe infection in sows. Poor conditions underfoot, particularly wet and stony, allow a breakdown of hoof horn integrity meaning various environmental pathogens track up to the corium. Abscessation follows, causing severe pain and swelling and potentially necrosis and sloughing. Prognosis is relative to promptness of intervention. The antibiotic of choice is lincomycin for seven days, as infection may be deep-seated.
Staphylococcus hyicus is an opportunistic pathogen in pigs, causing exudative epidermitis known as “greasy pig disease”. Usually seen in growing pigs, it can be serious as the toxins can have systemic effects.
When treating skin conditions it is important to consider tissue penetration, but amoxicillin, cephalosporins, lincomycin and tylosin are usually effective. Therapy may need to be extended to seven days or more, but recovery can be encouraged by soapy washing and topical antibiotics if practical.
Mange is common in pigs, causing pruritus, erythema and crusting. Sarcoptes scabiei has a predilection for the ears, so more subtle signs include increased wax production; skin thickening in the canal; head shaking and, as a consequence, aural haematomas. The welfare implications of pruritic disease are obvious, but productivity is also likely to be compromised as the stress might reduce feed intakes.
A possible sequel condition is an allergic reaction presenting as extensive papular lesions. Blunt ear skin scrapes can be taken for confirmation.
The treatment of choice is doramectin, although ivermectin is usually effective too. The parasite can survive off host for a few days, so it is often necessary to repeat therapy at 14 days – the duration of the mite’s life cycle.
Environmental treatment is advisable after treatment including pressure washing, disinfection, drying and resting. For the same reason the whole group, plus in-contact animals, should be treated simultaneously. Doramectin has a licensed claim for 18 days’ protection against reinfection, while ivermectin would be expected to cover for around 9 days (Arends et al, 1999).
Mild mange may be confused with pediculosis since this also involves pruritus and has an affinity for the ear. Only the sucking louse – Haematopinus suis – is likely to be seen and may be visible to the naked eye, allowing definitive diagnosis on clinical exam. Treatment is the same in any case – doramectin or ivermectin. The life cycle can be around three weeks, so repeat treatment may still be necessary.
Allergic response to mange should be differentiated from pig pox virus, which may be concurrent with mange, as mites potentially carry the virus. Other risk factors include lice and skin abrasions, such as fight wounds. Lesions are typical pox type with a necrotic centre developing, 1cm to 2cm in diameter and most commonly seen along the belly and flanks.
Acute erysipelas is also a major consideration for skin lesions, especially if red, raised and diamond-shaped. Pyrexia would be an expected additional sign. Penicillins are the antibiotics of choice, but tylosin is effective as well. In its chronic form erysipelas may also cause arthritis, infertility and endocarditis.
Neurological disease in pigs points primarily to infectious meningitis and is most common in sucking piglets and weaners. They could be obtundent, and nystagmus, shivering, paddling, convulsions and death would be typical, although other conditions may mimic this, such as salt poisoning (water deprivation), septicaemia and Glässer’s disease. Streptococcus suis is the most common, but not sole, agent responsible. The antibiotic of choice is penicillin, which should be given at least twice daily.
Mastitis sometimes features pyrexia, but is identified by pain of the udder, hard swellings, discolouration and agalactia. Sucking piglets will often treat an agalactic udder aggressively, so bite marks can provide a clue to this. If milk can be expressed it may be watery, clotted or bloody and aseptically collected samples could be taken for culture. If treatment is unsuccessful or further cases occur, the pretreatment sample is invaluable.
Appropriate antimicrobials include most beta-lactams and potentiated sulphonamides. Fluoroquinolones should be effective, but are regarded by many as a secondary choice on the basis of responsible use. NSAIDs must be included to combat toxic shock, even if pyrexia is absent. Oxytocin can be a useful adjunct to assist hand stripping, which is valuable in removing the infected milk.
Purulent or foetid vulval discharge indicates metritis and is frequently associated with mastitis after farrowing. Commonly known as mastitis, metritis and agalactia syndrome (MMA), this is related both to suboptimal hygiene and negative energy balance.
Typical organisms found in the uterus include Trueperella pyogenes (formerly Arcanobacterium pyogenes), Actinobacillus suis, Staphylococcus species and coliforms. Penicillins are the antibiotics of choice, but if discharge is present within a week of farrowing, and in the absence of mastitis or systemic signs, then antibiosis is not indicated.
