Zoonotic Diseases: Academic Review

This is a vast topic — my search returned several comprehensive reviews cataloguing 62+ zoonotic diseases shared between dogs and humans. Here's a structured overview of what I found, organized by pathogen type and with geographic notes where the literature provides them.

Bacterial zoonoses are the most extensively documented category. The major dog-transmitted bacterial pathogens include Leptospira spp., Pasteurella spp., Salmonella, Campylobacter, Brucella canis, Capnocytophaga canimorsus, Bordetella bronchiseptica, Coxiella burnetii (Q fever), MRSA, and Yersinia enterocolitica. Vector-borne bacterial zoonoses carried by dogs include Borrelia burgdorferi (Lyme disease), Ehrlichia spp., Anaplasma spp., Rickettsia rickettsii (Rocky Mountain spotted fever), and Yersinia pestis (plague).

Geographically, a scoping review of North American canine zoonoses research (507 publications) found the five most-studied pathogens were Ehrlichia spp. (16%), Borrelia burgdorferi (13%), Leptospira spp. (11%), rabies virus (8%), and influenza viruses (8%). Leptospirosis shows particularly striking regional variation: a 2025 systematic review covering 13,827 dogs across 12 countries found seroprevalence ranging from 9% to 75%, with the highest rates in South America and Asia, driven by tropical climates, proximity to water, and socioeconomic factors. In Spain, a large survey of 4,643 dogs found Leishmania infantum seroprevalence of about 10%, Dirofilaria immitis at 6%, Anaplasma spp. at 5%, and Ehrlichia canis at 4%, with both Leishmania and Dirofilaria expanding northward.

Viral zoonoses from dogs are fewer in number but include the most consequential: rabies remains the leading dog-transmitted viral zoonosis globally, causing tens of thousands of human deaths annually, overwhelmingly in Africa and Asia where canine vaccination coverage is low. Norovirus transmission from dogs to humans has also been documented. The COVID-19 pandemic brought attention to SARS-CoV-2 in dogs, though the comprehensive review by Macpherson et al. (2022) classified this as Category 3 — rare, with dogs only occasionally implicated.

Reverse zoonoses (human-to-dog transmission) are an emerging concern. A 2024 systematic review covering 91 articles found that respiratory viruses (SARS-CoV-2, influenza) and bacteria like Mycobacterium tuberculosis and MRSA are the most commonly documented human-to-animal pathogens. The US, India, and Hong Kong were the most frequently reported regions for these events.

Fungal zoonoses are less prominent in the literature but clinically important. Microsporum canis is a well-known cause of dermatophyte infections transmissible from dogs to humans. A study in Kerala, India found Trichophyton spp. (68%) and Microsporum spp. (32%) as the dominant dermatophytes in dogs. Malassezia pachydermatitis, part of normal canine skin flora, has caused severe infections in neonates and immunocompromised patients via healthcare workers who owned dogs. In southern Mexico, stray dogs were found carrying Aspergillus spp. (predominantly A. niger) in about 36% of dogs with skin lesions. Blastomyces dermatitidis is now considered endemic in southern Saskatchewan, Canada, based on a 21-year retrospective of canine cases.

Parasitic zoonoses arguably represent the broadest category. The most important globally are Echinococcus granulosus (cystic echinococcosis), Leishmania infantum (visceral leishmaniasis), Toxocara canis (visceral/ocular larva migrans), Trypanosoma cruzi (Chagas disease, Latin America), hookworms (Ancylostoma spp.), Giardia, and Cryptosporidium. Visceral leishmaniasis in dogs is found in roughly 50 countries, with millions of infected dogs — Brazil, Mediterranean Europe, and parts of Asia are hotspots, and the disease is expanding northward in Europe. In Colombia, intestinal parasites were found in 68% of dogs examined, with Ancylostoma spp. (30%) and Giardia (14%) most common — both transmissible to humans.

The most comprehensive categorization I found is by Macpherson et al. (2022), which classified 62 dog-human shared zoonoses into three tiers: 13 diseases where dogs are essential to maintenance and transmission (including rabies, leptospirosis, leishmaniasis, echinococcosis, and toxocariasis), 24 where human/dog behavior drives transmission (including bite-wound infections, tick-borne diseases, dermatophytes), and 25 where the dog link is rare but documented.

A true country-by-country breakdown with prevalence data for each pathogen is beyond what a quick search can assemble — it would require a structured table drawing on dozens of regional surveillance studies. This initial scan gives a reasonable landscape, but extended thinking could build a more systematic geographic comparison.

My search returned a rich set of sources on how farm dogs participate in zoonotic disease cycles. Here's the landscape, organized by the major pathogen groups.

The dog as a uniquely positioned bridge species on farms

A cross-sectional study of Ohio livestock farms by Moran et al. (2018, Zoonoses and Public Health) provides the clearest picture of the problem's scope. Of 446 livestock farm owners surveyed, 67% owned dogs; 70% allowed those dogs direct access to livestock; 76% rarely or never picked up dog feces; and 96% reported at least one high-risk dog–livestock management practice. Critically, about 52% of dog-owning households included someone at higher disease risk (young children, elderly, immunocompromised), yet over 90% expressed little to no concern about disease transmission between dogs and livestock or dogs and people. This combination — high contact, poor biosecurity, low awareness — defines the risk environment.

Echinococcosis / hydatid disease: the classic dog–livestock–human cycle

The most thoroughly documented zoonotic cycle involving farm dogs is Echinococcus granulosus. Dogs are the definitive host, harboring the adult tapeworm in their intestine and shedding eggs in feces; livestock (especially sheep) serve as intermediate hosts developing hydatid cysts; and humans become accidental intermediate hosts by ingesting eggs. The cycle perpetuates when dogs eat raw offal from infected livestock — a practice that remains common where home slaughter occurs.

A study of shepherd dogs in Tuscany found 78% of farms positive for at least one intestinal parasite, with Toxocara spp. on 64% of farms and taeniids on 32%. Although no E. granulosus was detected in that particular study, the widespread presence of related taeniids (T. hydatigena, T. multiceps) confirmed that dogs still have access to raw offal — the key risk behavior for E. granulosus transmission. In mid-Wales, an older survey found 25% of farm dogs infected with E. granulosus, with nearly 59% of farms harboring at least one infected dog. Iceland's historical experience is instructive: when 20–25% of the human population was estimated to be infected around 1850, the dog-to-human ratio was roughly 1:3–4, and dogs shared living quarters with families. Targeted public education and dog management essentially eliminated the parasite by the early 1900s.

Neospora caninum: a bidirectional dog–cattle cycle

Dogs are the definitive host for Neospora caninum, the leading cause of bovine abortion worldwide. The transmission is bidirectional: dogs become infected by consuming bovine placenta, aborted fetuses, or uterine discharge, then shed oocysts that contaminate cattle feed. Dijkstra et al. (2002) compared 12 herds with evidence of postnatal N. caninum infection to 21 control herds and found that on infected farms, dogs consumed placenta on 75% of farms and defecated on feeding alleys on 92%, versus 38% and 24% on control farms.

The seroprevalence data are striking. In New Zealand, dairy-farm dogs had a 74.5% seroprevalence to N. caninum versus 30.7% in urban dogs, and farms with dogs had significantly higher cattle seroprevalence than farms without. A Uruguayan national survey of 4,223 dairy cattle across 102 herds found animal-level seroprevalence of 22.3%, with the number of dogs on farms significantly associated with infection levels. In Galicia (Spain), seroprevalence was higher on farms with dogs, and infected cows were 5.3 times more likely to abort. While Neospora is not directly zoonotic (it does not infect humans), the dog–cattle cycle causes substantial economic losses and illustrates how farm dogs function as amplifiers of inter-species pathogen transmission.

Leptospirosis and brucellosis: bacterial spillover

Farm dogs are exposed to Leptospira spp. and Brucella spp. through contact with infected livestock urine, reproductive tissues, and contaminated water. A Brazilian survey of rural dogs found 25% seropositive for Leptospira and 25% for Brucella ovis, with 75% of the 32 properties studied positive for leptospirosis. Dogs in contact with brucellosis-positive cattle in Argentina showed 7.5% confirmed seropositive for B. abortus — a species typically associated with cattle rather than dogs — highlighting cross-species transmission. Free-ranging behavior was consistently identified as a risk factor for both infections across multiple studies.

Parasitic sentinel role and vector-borne diseases

Farm and rural dogs also serve as sentinels for broader zoonotic parasite circulation. A 4-year survey of stray dogs in Pakistan found 24.4% positive for intestinal parasites, with Ancylostoma caninum and Toxocara canis most prevalent, and Echinococcus/Taenia the most geographically widespread. In rural Portugal, 59% of farm dog fecal samples were parasite-positive, with home slaughter a significant risk factor for Ancylostoma and Toxocara infection. In the Argentine Chaco, 77% of the 17 parasite species found in dogs were zoonotic, and 96% of dogs showed polyparasitism.

Dogs' ectoparasites add another layer: a 2024 study in rural Guatemala found Rickettsia felis and Bartonella henselae in dog fleas and ticks, demonstrating that dogs concentrate vector-borne zoonotic pathogens and serve as a bridge for human exposure.

The key gaps and takeaways

The consistent finding across these studies is a mismatch between risk and awareness. Farmers routinely allow dogs access to livestock, birthing materials, and feed storage areas while expressing minimal concern about disease transmission. Control strategies that have proven effective historically — restricting dogs' access to raw offal, deworming programs, fecal management, and public education — are straightforward but underimplemented, particularly in developing countries and small-scale farming operations.

This is from an initial search pass, and a topic this broad certainly has more literature than what I've captured here — particularly on specific pathogens like Toxoplasma gondii, Cryptosporidium, and Q fever where dogs may play secondary transmission roles.

Applied Field Scenarios & FAQ

Using the data presented in the literature above, here is how to handle specific field situations with your LGD.