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Small-scale pig keeping: prohibiting zoonotic pathogens

Research scientist and pig farmer Dr Michaela Giles continues her series of insights for smaller herds with tips for protecting yourself and farm visitors from zoonotic pathogens.

19 April 2019, at 10:30am

A zoonotic disease is one that can be spread between animals and people. The risks to the small-scale pig keeper of catching a disease from pigs are minimal but shouldn’t be ignored; even if you only keep a couple of weaners to rear for meat.

Infectious diseases are transmitted in a variety of ways depending upon the organism: 1) airborne; 2) direct contact with the pig including skin, mucus membranes; and 3) indirect contact with faeces, urine, blood, insect vectors, contaminated food and water.

The most vulnerable to contracting zoonotic diseases from pigs are immunocompromised people such as the elderly, young children, pregnant women and those with medical conditions that affect the immune system. for example, cancer or transplant patients.

In developed countries, commercial farms perform proactive disease monitoring and control so the risk of zoonotic disease contraction is low. Small-scale keepers, however, are likely to keep their pigs outdoors, where disease risks are higher and do not routinely monitor for disease status. In addition, weaners sold to smallholders for meat production are unlikely to be vaccinated against diseases, although when purchased from a reputable breeder they are dewormed.

Some countries, such as the UK, are officially free from some zoonotic diseases, such as Trichinellosis and Brucellosis, through proactive control measures. The risk of transmitting and contracting other zoonotic diseases, however, remains present.

Neurocysticercosis is caused by ingestion of the larval cysts of tapeworms in infected undercooked pork
Neurocysticercosis is caused by ingestion of the larval cysts of tapeworms in infected undercooked pork

Parasites

Cysticercosis is a tapeworm infection, predominantly caused by Taenia solium, is acquired by humans through the ingestion of larval cysts in infected undercooked pork, potentially causing neurological symptoms, including epileptic seizures.

Ascaris suum, a ubiquitous round worm which is responsible for ‘milk spot’ scarring of the pigs’ liver – a common cause of the liver being condemned at the abattoir. In humans, acute respiratory failure has been reported.

Trichinella spiralis is a nematode worm capable of infecting a wide range of mammals. Pigs infected with Trichinella show no obvious signs of disease unless the load is severe. In humans, infection is from the consumption of undercooked meat containing Trichinella larvae. The symptoms are variable, including: fever, muscle and joint pains, diarrhoea and swelling around the eyes and, in severe cases, potentially fatal neurological or cardiac complications.

Viruses

Swine influenza is perhaps the most potentially dangerous zoonotic disease known to infect pigs. This is because flu viruses have segmented genomes (genes), which can mutate to make new viruses, potentially creating a more pathogenic virus in humans. It’s a low short-term risk but remains a concern over a longer time frame. Direct transmission between species is much less common.

Hepatitis E results in no clinical signs in pigs. In humans the signs include mild fever, lack of appetite, nausea, vomiting for a few days followed by abdominal and joint pain, itching, skin rash, jaundice with dark urine, and pale faeces.

Bacteria

Erysipelas, caused by Erysipelothrix rhusiopathiae, which may cause diamond-shaped skin lesions, lameness and abortions in infected pigs, is transmitted by direct skin-to-skin contact, most frequently through a wound in the skin. Erysipelas infections in humans can result in the following clinical signs: skin lesions in the form of vesicles or blisters, fever, fatigue, headaches, vomiting and lymphedema.

Escherichia coli (E. coli), Salmonella spp., Campylobacter spp. and other bacterial diseases can cause diarrhoea in pigs and intestinal discomfort and diarrhoea in humans, occasionally leading to serious dehydration. It is important to note that the infamous E. coli 0157 causing serious symptoms including kidney failure in humans is not normally found in pigs.

Leptospira species causes reduced appetite, abortion, fever, diarrhoea and neurological signs in pigs and fever, headache, muscle ache, vomiting and liver/kidney failure in humans.

Streptococcus suis causes uncoordination, blindness, paralysis and convulsions in pigs. It can cause meningitis, sepsis, heart disease and skin lesions in humans.

Fungi

Ringworm is a fungal disease that can be highly contagious. Clinical signs in pigs include crusty, dark hairless patches commonly around the head and neck and behind the ears before spreading. In humans, the symptoms may consist of a ring-shaped red or silver rash that is scaly, dry, swollen or itchy. Ringworm can also be spread by infected rodents.

If the disease status of your pigs is unknown, it makes sense to keep hand to mouth contact to a minimum when handling your pigs, especially incoming pigs. Incorporating hand washing with soap into your routine, before and after visiting your pigs is a first step
If the disease status of your pigs is unknown, it makes sense to keep hand to mouth contact to a minimum when handling your pigs, especially incoming pigs. Incorporating hand washing with soap into your routine, before and after visiting your pigs is a first step

Minimising the risks

  • The biggest risk of a pig catching a disease is from another pig so when you hire in boars, buy new stock or exhibit your pigs, biosecurity precautions should be followed before mixing incoming pigs with the main herd, including the use of isolation pens. You cannot catch a disease if it isn’t in your herd.
  • If the disease status of your pigs is unknown, it makes sense to keep hand to mouth contact to a minimum when handling your pigs, especially incoming pigs. Incorporating hand washing with soap into your routine, before and after visiting your pigs is a first step.
  • Caring for the main herd before attending the pigs in isolation is a must.
  • Don’t let other pig keepers have access to your pigs unless they have been 48 hours free of contact.
  • Use disinfection footbaths for all visitors to the farm or, better still, provide footwear for them.
  • House the pigs away from any public rights of way on your land.
  • Maintain good rodent control.
  • If you are suffering from flu then do not attend your pigs until you have recovered.
  • There are other zoonotic diseases that a pig keeper may encounter including from other kept species and wildlife, so it is worth familiarising yourself with them.