Zoonotic diseases in companion animals

6 July 2023


Zoonoses are infectious diseases that can be transmitted between animals and humans.

With an increase in the number of companion animals being imported into the UK and the changing climate which may alter the distribution of disease vectors1, there is a growing risk of both non-endemic diseases with zoonotic potential occurring in the UK (and ultimately becoming endemic) and the capacity for their transmission by arthropod vectors. The chance of encountering animals with zoonoses is ever present for veterinary professionals, as well as for pet owners.

To mark this year’s World Zoonoses Day, we’re summarising the key facts about some zoonotic diseases that you might see in practice.


What is its prevalence in the UK?

Canine leishmaniosis is a vector-borne disease caused by a protozoan parasite that is spread by phlebotomine sand-flies and causes severe fatal disease in dogs and humans globally1,2.

Leishmaniosis is endemic in the Mediterranean, the Middle East, and some tropical and subtropical regions, where sand-flies are widespread2. The causative parasite (usually Leishmania infantum) is not endemic to the UK, and most dogs that present with leishmaniosis have a history of travel or have been imported from endemic areas. Very rarely, leishmaniosis is seen in non-travelled dogs that have been in close contact with infected dogs1,2.

How is it transmitted?

The main route of transmission is via sand-fly bites, but non-vectoral transmission can occur horizontally through traumatic and non-traumatic direct contact and venereal contact, vertically, and iatrogenically (via blood transfusion)3.

What are the clinical signs?

There are a wide variety of clinical signs, ranging in severity from mild and self-limiting to fatal3. Local cutaneous lesions at the site of the initial bites (ear pinnae, nose and abdomen) are often the first signs of infection5. Other clinical signs include the classical, often symmetrical exfoliative dermatitis and peri-ocular alopecia, pyrexia, weight loss, lymphadenopathy, pallor, gastrointestinal disorders (reduced appetite, vomiting, diarrhoea, colitis), polyarthritis (manifesting as reluctance to exercise and lameness due to swollen, painful joints), glomerulonephritis (manifesting as polyuria / polydipsia; progressing to kidney failure with or without nephrotic syndrome), splenomegaly, and ocular signs (conjunctivitis, blepharitis, uveitis)3,4,5.

How is it diagnosed?

Accurate diagnosis requires an integrated approach combining physical examination, clinicopathological tests and specific laboratory tests3,6.

Antibody serology is the most commonly used first step, and intervals for seroconversion in naturally infected dogs can take from 1 to 22 months (median 5 months)7. The sensitivity and specificity of serological tests (IFAT and ELISA) is generally good, but the sensitivity of rapid (qualitative) serological test kits can be variable3. Not all animals seroconvert, and some dogs can take several months to develop antibodies1. Most assays are optimised to L. infantum and their sensitivity at detecting antibodies directed at other species is often not described.

PCR assay can be carried out on blood samples or tissue aspirates (e.g. from lymph nodes and bone marrow)3. Direct diagnosis is sometimes possible by detecting the amastigote stages in stained smears obtained from enlarged peripheral lymph nodes, skin nodules, spleen, liver, bone marrow, other internal organs and, occasionally, body fluids3,5.

How is it treated?

The combination of allopurinol with either meglumine antimonate or miltefosine is considered first line in most dogs with clinical disease6. It’s worth noting that no medication is 100% effective in eliminating infection and even if there is a clinical cure, the dog may remain a carrier and a reservoir of infection3.

What is the risk to humans?

Dogs are thought to be the main reservoir for leishmaniasis in humans, with transmission via bites from infected sand-flies3. However, in the absence of the sand fly vector, the risk of transmission from an infected dog is thought to be extremely low (it has not been described)3. Human leishmaniasis typically causes skin lesions, which are often self-healing within a few months but leave scars. Other common symptoms are fever, malaise, weight loss, and anaemia8. In Europe, most human cases are associated with immunosuppressive diseases such as HIV3.

Find out more in BSAVA’s Leishmaniosis Scientific Information Document. https://www.bsavalibrary.com/content/chapter/10.22233/9781910443514.chap3#html_fulltext


Canine brucellosis

What is its prevalence in the UK?

Canine brucellosis is an infectious and zoonotic disease caused by Brucella canis; an intracellular, Gram-negative coccobacillus9. It is a reportable disease in Great Britain and is notifiable in Northern Ireland.

Brucella canis has a widespread distribution, and is thought to be endemic in eastern and central Europe, and parts of North and South America, Asia and Africa9. It is not endemic in the UK, but there has been an increase in the number of dogs diagnosed since 2020, with most cases in dogs imported from Eastern Europe or other areas considered endemic9.

How is it transmitted?

Brucella canis infection is usually acquired via venereal or vertical transmission. It is also shed in aborted material, vulval discharge, semen, and urine, and can result in non-venereal horizontal transmission to exposed dogs (and humans). Brucellosis can be transmitted via blood products9,10.

What are the clinical signs?

Most dogs infected with B. canis are subclinical9. The main clinical sign is reproductive disease; however, this may go unnoticed particularly in neutered or non-breeding animals. In females, signs include infertility and/or abortion late in pregnancy between 45-59 days, and purulent vulval discharge. In males, signs include purulent preputial discharge, epididymitis, testicular atrophy or orchitis, scrotal dermatitis, prostatitis, and infertility9,10. Discospondylitis (manifesting as vertebral pain and neurological deficits) is a common reason for presentation in dogs with clinical brucellosis in non-endemic countries. Other very non-specific signs include lymphadenopathy, splenitis, lethargy, uveitis, hyporexia, and weight loss9,10.

How is it diagnosed?

Serology is used to detect exposure to Brucella canis. Test sensitivity is typically high, although false negative results are possible with acute and very chronic (subclinical) infection9.

The following serology tests are available in the UK: serum agglutination test (SAT); indirect enzyme-linked immunosorbent assay (iELISA); Rapid slide agglutination test (RSA); and point-of-care tests (immunomigratory a.k.a. lateral-flow tests or semi-quantitative iELISAs). If one or more of SAT, iELISA, or RSA is positive then the dog is considered serologically positive for B. canis (even if one or more of the other tests are negative)9.

PCR and bacterial culture should not be used to screen at-risk dogs, as sensitivity is poor, with positive results often only seen in early infection/acute clinical disease9.

How is it treated?

Treatment is generally not recommended, due to lack of effective procedures to consistently clear infection and ongoing risk of transmission to dogs and humans. Euthanasia is the only option to eliminate all ongoing risk of transmission9.

In cases where owners choose not to euthanise, efforts to reduce risk of transmission should be considered. This includes isolating infected dogs from other dogs and allowing only limited contact with people (particularly vulnerable or immunocompromised), neutering, and regular serological monitoring9. If treatment is pursued, options comprise extended courses of multiple antimicrobials capable of intracellular penetration (e.g. doxycycline, aminoglycosides, fluoroquinolones, rifampicin), although none are considered 100% successful, and relapses of clinical disease are common9. If opting for treatment with antibiotics, antimicrobial resistance needs to be taken into consideration.

What is the risk to humans?

Human cases of Brucella canis infection are rare, although likely underdiagnosed9. Transmission is primarily attributed to ‘high-risk’ exposure events, including direct contact with purulent material, birth or abortion products, and handling of cultured material from a Brucella-positive dog9. Clinical signs in human cases are generally nonspecific and include fever, chills, malaise, splenomegaly, and peripheral lymphadenopathy11.

Find out more in BSAVA’s Brucella canis Scientific Information Document. https://www.bsavalibrary.com/content/chapter/10.22233/9781910443514.chap9#html_fulltext


Lyme disease

What is its prevalence in the UK?

Lyme disease is a chronic, multi-systemic, inflammatory disorder of animals and humans, associated with infection by the tick-borne spirochaete, Borrelia burgdorferi sensu lato12. Lyme disease is a significant threat to dogs exposed to ticks in the UK13.

How is it transmitted?

Lyme disease is transmitted via a bite from an infected tick; the principal vector in the UK is Ixodes ricinus12.

What are the clinical signs?

Most infections are subclinical, with 5-10 percent of infected dogs developing clinical signs13. Lyme disease most commonly manifests as a non-erosive inflammatory arthropathy12. The typical presenting signs are a migratory arthritis (shifting lameness), usually only affecting up to five joints. Other signs may follow, including fever and lymphadenopathy12. Lyme nephritis is not considered common in affected dogs in the UK and nor do they exhibit a target rash as is observed in humans. Clinical manifestations of Lyme disease in naturally-infected cats are uncommon5,12.

How is it diagnosed?

Diagnosis usually depends on evidence of exposure, in conjunction with clinical signs and diagnostic testing9. Direct diagnosis by culture, cytology, or PCR may be difficult because B. burgdorferi is rarely found in blood, urine, synovial fluid, or cerebrospinal fluid5,12. In serum, Borrelia antibodies can be detected using immunochromatographic tests and usually appear 3–5 weeks after infection, before the onset of clinical signs5. However, although a positive serological test indicates exposure to the pathogen, it does not equate to a diagnosis of Lyme disease12.

How is it treated?

Four weeks of doxycycline or amoxycillin is usually effective if recognised early13. Most cases have an excellent prognosis if diagnosed and treated promptly12. However, if not recognised early, chronic disease can develop which can potentially lead to non-erosive polyarthritis and protein losing nephropathy13.

What is the risk to humans?

As with dogs, Lyme disease can be transmitted to humans via tick bite14. However, dogs are considered a sentinel for human infection rather than reservoir and there is no evidence that Lyme disease can spread directly from dogs to humans15. Early signs of Lyme disease include a circular red rash at the site of the tick bite, followed by flu-like symptoms, and if untreated, can progress to neurological problems and arthritis12,14.

Find out more in BSAVA’s Lyme disease Scientific Information Document. https://www.bsavalibrary.com/content/chapter/10.22233/9781910443514.chap5#html_fulltext


Echinococcus multilocularis (Fox tapeworm)

What is its prevalence in the UK?

Echinococcus multilocularis is a tapeworm that can infect dogs and other canids (the main host being the red fox)16. There have been no known domestically-acquired cases of E. multilocularis in the UK but the number of cases in continental Europe appear to be increasing16,17. It is a notifiable disease16.

How is it transmitted?

The tapeworm is transmitted when dogs eat infected rodents, which are the intermediate hosts16. Cats can also become infected but are likely to excrete fewer eggs and consequently pose less of a threat for transmission17.

How is it diagnosed?

Normally, the tapeworm causes no obvious clinical signs in dogs, but occasionally infected dogs may develop alveolar cysts in the liver, brain, or other parts of the body and show clinical signs that resemble tumours17,16. The eggs of E. multilocularis tapeworm will appear in the animal’s faeces, however, are only seen when a faecal sample is examined under a microscope16.

How is it treated?

If bringing a dog into Great Britain from another country, a vet must treat it for tapeworm no less than 24 hours and no more than 120 hours before entry, and record it in the pet passport or health certificate18. Similarly, if a dog is being taken outside of Great Britain for a short trip, the dog must be treated before it travels, and should be treated again within 28 days of returning18.

It is recommended that dogs are treated with a worming treatment that contains praziquantel or an equivalent proven to be effective against the E. multilocularis tapeworm16.

What is the risk to humans?

Echinococcus multilocularis is probably the most dangerous of all helminth diseases in humans and can cause serious illness16,17. Humans become infected after consuming eggs from contaminated environments and act as dead-end hosts16. Echinococcus multilocularis can result in the formation of cysts which proliferate and cause a tumour-like growth. Advanced disease symptoms are cholestatic jaundice, epigastric pain, fatigue, weight loss, and hepatomegaly17.

We have put together a collection of resources on zoonotic diseases in the BSAVA library, which is free to access for the month of July. https://www.bsavalibrary.com/content/zoonotic-diseases


1APHA (2022) Imported diseases summaries for Dogs and Cats. August 2022. Available at: < http://apha.defra.gov.uk/documents/surveillance/diseases/imported-dog-disease-for-dog-and-cats.pdf>

2Shaw SE, Langton DA, Hillman TJ (2009) Canine leishmaniosis in the United Kingdom: A zoonotic disease waiting for a vector? Veterinary Parasitology. 163(4), 281-285. https://doi.org/10.1016/j.vetpar.2009.03.025.

3BSAVA (2016) Leishmaniosis (Scientific Information Document). Available at: <https://www.bsavalibrary.com/content/chapter/10.22233/9781910443514.chap3#html_fulltext>

4McGrotty Y (2022) IDEXX topic of the month: Canine leishmania – a quick guide. BSAVA Webinar Library. Available at: < https://www.bsavalibrary.com/content/chapter/10.22233/9781910443491.ch156>

5ESCCAP (2019) Modular Guide Series: Control of Vector-Borne Diseases in Dogs and Cats. Available at: <https://www.esccap.org/uploads/docs/okkgb4dw_1058_ESCCAP_MG5__English_v12.pdf>

6Solano-Gallego L & Baneth G (2012) Canine leishmaniosis. From: BSAVA Manual of Canine and Feline Haematology and Transfusion Medicine. Ch 20, pp174-181. British Small Animal Veterinary Association.

7Moreno J & Alvar J (2002) Canine leishmaniasis: epidemiological risk and the experimental model. Trends Parasitol. 18, 399–405.

8European Centre for Disease Prevention and Control (2023). Facts about leishmaniasis. Available at: <https://www.ecdc.europa.eu/en/leishmaniasis/facts>

9BSAVA (2023) Brucella canis (Scientific Information Document). Available at: <https://www.bsavalibrary.com/content/chapter/10.22233/9781910443514.chap9#html_fulltext>

10McGrotty Y (2022) IDEXX topic of the month: Canine brucellosis: what you need to know. BSAVA Webinar Library. Available at:


11Public Health England (2022) Human Animal Infection and Risk Surveillance Group. Available at: <https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/960013/20210210_Brucella_canis_statement.pdf>

12BSAVA (2016) Lyme disease (Scientific Information Document). Available at: https://www.bsavalibrary.com/content/chapter/10.22233/9781910443514.chap5#html_fulltext

13Wright I (2018) The risk of Lyme disease exposure to UK dogs. InFocus. Available at: <https://www.veterinary-practice.com/article/the-risk-of-lyme-disease-exposure-to-uk-dogs>

14UK Health Security Agency (2022) Lyme diseases: signs and symptoms. Available at: <https://www.gov.uk/government/publications/lyme-disease-signs-and-symptoms/lyme-disease-signs-and-symptoms>

15Pet Health Network (2023) Can Lyme Disease in Dogs Spread to People? Available at: <https://www.pethealthnetwork.com/dog-health/dog-diseases-conditions-a-z/can-lyme-disease-dogs-spread-people>

16Bonner J (2009) Problematic parasite to pet and owner. BSAVA Companion. 6, 15-17. DOI: https://doi.org/10.22233/20412495.0609.15

17GOV.UK (2019) Echinococcus multilocularis: how to spot and report the disease. Available at: <https://www.gov.uk/guidance/echinococcus-multilocularis-how-to-spot-and-report-the-disease>

18GOV.UK (2023) Bringing your pet dog, cat or ferret to Great Britain. Available at <https://www.gov.uk/bring-pet-to-great-britain/tapeworm-treatment-dogs>