Stay safe

Michaela Giles explains the health implications around rodent populations and the importance of Farm Control Plans for you, your pigs and other animals

As a part of responsible food production and animal welfare, it’s important to have an effective rodent control plan in place. It may be an incentive to know the breadth of diseases that are transmissible by rodents.

Dead rodents must be handled with gloves

Dead rats must be handled with gloves, and disposed of responsibly. They can be double-bagged and put in your landfill dustbin. (Photo: Budimir Jevtic/Shutterstock)



Rats carry fungus, bacteria, endoparasites (internal) and viruses that can cause infections harmful to both humans and our pigs; rats have been linked to more human deaths than any other mammal. Their astonishing reproduction rate means that one pair of rats can produce 15,000 offspring in a single year. Experts estimate that there are approaching 60 million rats in the UK, and hungry rats have been observed to travel 2km at night, further increasing the disease risk between pig farms in areas of high pig density.

If that’s not enough to encourage a rodent control plan, they also act as host reservoirs for ectoparasites such as fleas, ticks, lice, and mites, which cause many more diseases and/or can be a welfare issue.

I have highlighted five of the possible diseases below.


Leptospirosis in pigs is usually a chronic infection caused by a bacterium called Leptospira Bratislava within the UK. While no clinical signs are observed in the pig, it is an important cause of elevated returns-to-service, thick vaginal discharges, whole herd infertility problems, abortions, stillbirths, and poor survival of newborn piglets. There may be some cases of pigs failing to thrive because of persistent kidney damage.

Other species of Leptospira also may cause disease in pigs. Leptospira Copenhageni causes abortions and stillbirths and can additionally cause lethargy, wasting, anaemia, jaundice and death, most commonly in growing pigs. Leptospira canicola in dogs can cause sporadic septicaemic disease in young piglets. Leptospira icterohaemorrhagiae, the cause of Weil’s Disease in humans, may also be seen as a systemic disease in young pigs causing lethargy, wasting, anaemia, jaundice and possible death.

Confirmatory diagnosis
Confirmatory diagnosis of species is generally performed using laboratory tests using serology to detect antibodies and/or DNA tests for the presence of Leptospira bacteria in aborted piglets or in the reproductive organs of culled sows.

Where the disease is confirmed, treatment of the whole herd with antibiotics is appropriate, either a single or double blanket treatment with eg, Streptomycin; or treatment of sows/gilts at time of service. Boars will need to be included as there is emerging evidence that venereal spread may occur.

There are no vaccines currently in the UK to control L. Bratislava, although they are available in Europe and can be imported by a veterinary surgeon under a Special Import Certificate if you have a severe problem.

A pair of rodents can produce 15,000 babies a year

A single pair of rats can produce 15,000 offspring in a year.
(Photo: Surakit Sawangchit/Shutterstock)


Salmonella typhimurium is the most common species found in pigs and is mostly associated with post-weaning scour, septicaemia and as a complication of other major systemic infections such as Porcine Reproductive and Respiratory Syndrome (PRRS). It is also a significant food-borne zoonotic infection (can pass from animals to humans), and increasingly there are concerns not only regarding its transfer as a disease-causing organism in humans but also the ability for it and other Salmonella variants to transfer antibiotic resistance to human pathogens via the food chain.

Salmonella cholerae-suis is another variant, which, although rarely found, causes serious disease in pigs. There are two clinical presentations;

  1. The septicaemic ‘cholera’ form – causing an acute septicaemic disease in young growing pigs. Mortality rates are high, and prior to death, they will be extremely ill – vomiting, depressed, laboured breathing and with a very high rectal temperature (41°C +). One of the chronic features of the disease is that the extremities will turn purple/blue, particularly the ears, scrotum, and feet.
  2. An enteric form – a much milder disease, Salmonella cholerae-suis can be involved in causing scour in young growing pigs, in which case it appears to be restricted to the gut. Mortality is low, although the disease can be debilitating and may be part of the complex of disease that has its foundation in Post Weaning Multisystemic Wasting Syndrome (PMWS) on farms where that disease is not properly controlled by vaccination.

Confirmatory diagnosis
Diagnosis of septicaemic/cholera forms of the disease is based on clinical presentation, post-mortem findings with a typical septicaemic carcass and culture of the causative organism. In the enteric form, the organism may appear almost as a surprise in an investigation of weaner scours.

If carefully chosen, antibiotics are highly effective at killing Salmonella cholerae-suis, and the veterinary surgeon will make appropriate recommendations based on the available information. Other clinical signs may be present on those pigs that survive eg, skin or extremity sloughing, as is commonly seen with other septicaemic conditions eg, Erysipelas, Glässers disease.



This is a skin condition caused by a range of species of dermatophyllic (skin-loving) fungi. Most species of ringworm – irrespective of their primary host – are capable of jumping species and producing disease. Frequently this cross-species infection can lead to a longer-term infection than in the primary host.

Pig ringworm is transmitted by rodents

Rat ringworm, seen here, is harder to spot than classic ringworm.

Within the UK, three types of ringworm are predominantly seen in pigs.

  1. Trichophyton verrucosum: the cattle ringworm – largely only seen in smallholder pigs in contact with calves.
  2. Microsporum canis: the dog ringworm is actually more common in cats and crosses over to pigs where cats and pigs mix. The most likely infection will be in nursery piglets where cats sleep in creep areas.
  3. Trichophyton mentagrophytes: the rat ringworm. This is most commonly seen in outdoor and indoor straw-based sows and is associated with bedding derived from stacks in which rats have nested or simply within an environment heavily contaminated by rats.


Differential presentations
Disease caused by Microsporum canis in young pigs is usually ‘ring’ like and damaging to the skin. Itching is typically seen, and the skin damage that results from the primary infection and the rubbing can precipitate greasy pig disease – an important and harmful bacterial dermatitis.

Rat ringworm in pigs can easily be mistaken for soil or faecal contamination of the skin and only produces a negligible itching. Occasionally appears as ‘rings’ but typically produces patches of up to 20cm in diameter, usually on the neck, shoulders or back, which are a brown to orangey colour. The disease can be seen as outbreaks in growers in heavily contaminated conditions, including straw yards.

No products are licensed for pigs and thus can only be applied under the cascade prescribing system by a veterinary surgeon. Where applicable, a topical treatment containing enilconazole would be prescribed.


“…  effective rodent control goes way beyond ‘buying poison’”

Toxoplasma gondii

Most Toxoplasma gondii infections in pigs show no outward clinical signs. Where signs are presented, it is most often being reported in nursing pigs. Infected pigs are born dead, mummified, sick, or become sick within three weeks after birth, with laboured breathing being the most common clinical sign. Other clinical signs include fever, general weakness, diarrhoea, nervous signs and, rarely, loss of vision.

The parasites can persist in the edible tissues of pigs indefinitely and are infectious to humans – although they are killed by cooking/freezing. The parasite has been found in virtually all body muscles of pigs.

Detection of antibodies to T. gondii by a blood test can aid diagnosis. Dead piglets should be submitted to diagnostic laboratories for necropsy and histologic evaluation.

There is no treatment for pigs other than breaking the life cycle by reducing rodent populations, keeping cats away from pigs, and sticking rigidly to the catering waste ban.

Rodent control can include wax bait

Wax bait blocks are clean and simple to use, but you have to be licensed to buy large quantities.
(Photo: Oliver Hewett/Shutterstock)

Escherichia coli

Neonatal diarrhoea (scour) is a common cause of loss in piglets soon after birth. There is a range of causes, but infection with the bacterium Escherichia coli causing colibacillosis remains one of the most common. Neonatal E. coli infection presents as a profuse watery scour within three days of birth, with severe and rapid dehydration. Vomiting is not typically seen. Death can occur rapidly – even in littermates – before scour is evident. It will often occur in whole litters and can spread from litter to litter, often via rodents, if additional rodent control measures are not in place.

Confirmatory diagnosis
Diagnosis is confirmed on laboratory testing of gut contents or rectal swabs. Histopathology on affected gut tissue will confirm E. coli damage and differentiate other pathogens eg, Rotavirus and coccidia.

Individual cases may be treated with an appropriate oral antibiotic, often determined by sensitivity testing, given at the earliest sign of diarrhoea. In an outbreak, strategic medication of all pigs at birth, under veterinary supervision, may be necessary. Of equal importance is the provision of electrolytes to reduce the severe dehydration that actually kills many piglets; in severely affected pigs, this needs to be proactively administered orally eg, by syringe.

Vaccinations are available for administration to sows/gilts before farrowing as one tool in preventing this disease.

Bait must be placed in rodent runs

Bait boxes should be placed along an established rat run, and it may take a few days for the rats to start using them. Check regularly and top-up as needed.
(Photo: Oliver Hewett/Shutterstock)

Other diseases

There are too many pathogenic organisms that, when present in the UK, can be spread (via faeces and urine, or mechanically) by rodents to provide an exhaustive list in this article. Notable examples include; parasites (tapeworm, Trichinella), viruses (Hantavirus, Foot & Mouth Disease, encephalomyocarditis) and bacteria (erysipelas, tuberculosis, Listeria monocytogenesClostridium difficileBordetella bronchiseptica).


Leptospira icterohaemorrhagiae, the cause of Weil’s Disease in humans”


Rodent control plans
Formulating an effective rodent control programme goes way beyond ‘buying poison’. Control is a multi-pronged approach including monitoring of the farm for evidence of rodents; discouraging rodents, eg, weed control around buildings/no access to pig food; efficient cleaning and disinfection to prevent the presence of spreadable pathogens; preventing access to buildings where straw and feed is stored; keeping the farm free of rubbish and debris; setting humane/instant-kill traps.

Only when these are all in place should you consider the use of poison to control rodent populations.

The Campaign for Responsible Rodenticide Use (CRRU) UK Code of Best Practice outlines the guidance and safe use of rodenticides. The guidance, updated in June 2021, has the full information to produce a bespoke rodent control plan for your pig farm. The AHDB and The Pig Site also have advice on formulating control plans for rodents.

Should you need to control rodents on your farm with rodenticides, from March 2018, anyone who wants to buy wheat-based rodenticide (rat bait, mice bait) over 150g or rat bait/mice bait in blocks over 300g must complete a rodent control course. This online rat poison course meets these requirements and also meets the standard set by the CRRU. Do double check that the course you take will give you a nationally recognised certificate of competence, which can then be used for buying professional use rat and mice baits.


Useful links

AHDB: Rodent Control on Farms

The Pig Site: Rodent Control on Farms

CRRU: Code of Best Practice


Live rodent trap

While humane traps may seem kinder than instant kill traps, you are left with the tricky problem of what to do with a scared, live rat. If you opt for these, you must check them at least twice a day.
(Photo: Trong Nguyen/Shutterstock)


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This article first appeared in the Winter 2021 issue of Practical Pigs. You can buy this issue here


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