Toxocara canis is a helminth zoonosis that is estimated to infect more than 100 million dogs and 1 billion people, mostly in the tropics. Humans can be infected by accidentally ingesting embryonated T. canis eggs from the environment or occasionally after ingesting L 3 larvae from paratenic hosts. This study investigated the importance of vertical transmission and the role of puppies in the epidemiology of T. canis through the examination of fecal samples from dogs less than one year of age in Grenada, West Indies, a small island tropical developing country. Samples were stored at 4 °C or in 10% formalin until microscopic examination for helminth eggs or using a rapid antigen test for the presence of protozoan species. A knowledge, attitudes and practices study was completed among dog owners, physicians and veterinary students. Of 306 dogs less than one year of age, 147 (48%) were found to have T. canis eggs. Vertical transmission was indicated by the proportion of infected dogs increasing from 50% at two weeks of age (from in utero transmission) to 70% by 12 weeks (in utero and lactogenic transmission). After 12 weeks the positivity rate dropped rapidly with no dogs over 40 weeks of age being infected. As T. canis eggs were found in puppy feces at two weeks of age, initial treatment of puppies should begin earlier, at twelve days post-partum, than currently recommended to prevent shedding of eggs. Perhaps even more importantly, treatment of pregnant dogs, preventing vertical transmission, would have a major impact on the control of T. canis infection. Knowledge of T . canis and other zoonotic helminths such as Ancylostoma caninum was found to be low among dog owners, physicians and veterinary students. None of the dog owners treated their dogs for helminths, all were unaware of the risk of zoonoses, and only 9% picked up dog feces. Efforts to prevent vertical transmission and to increase awareness and knowledge of these zoonoses could result in reducing their public health impact.

Ancylostoma ceylanicum hookworms are recognized agents of human infection in the Asia–Pacific region. We investigated prevalence of zoonotic hookworm infections in dogs in Grenada in 2021; 40.8% were infected by hookworms, including Ancylostoma ceylanicum . Surveillance of this parasite in dogs and humans is needed in tropical/subtropical countries in the Americas.

This review categorizes 62 zoonoses humans share with dogs based on their clinical, public health importance, and global distribution. Three categories were identified. Category 1 comprise the most widespread and public health important zoonoses and includes 13 zoonoses where dogs play an essential role in the maintenance and transmission of the infectious organisms. This category comprises Rabies lyssavirus , Leptospirosis, Leishmania, Trypanosoma cruzi, Trypanosoma brucei spp ., Clonorchis sinsensis, Opisthorchis viverrini, Paragonimus spp ., Echinococcus granulosus, Echinococcus multilocularis, Taenia multiceps, Dracunculus medinensis, Toxocara canis, Ancylostoma spp ., and Strongyloides stercoralis. Category 2 includes 24 zoonoses of lesser public health importance in which human or dog behavior plays a major role in transmission. Category 2 includes, Microsporum spp ., Prevotella spp ., Bacteroides spp ., Porphyromonas spp ., Bergeyella zoohelcum, Neisseria spp ., Pasteurella spp ., Capnocytophaga canimorsus, Staphylococcus spp ., Streptococcus spp ., Salmonella spp ., Anaplasma spp ., Ehrlichia spp ., Borrelia spp ., Rickettsia spp ., Yersina pestis, Giardia duodenalis, Cryptosporidium spp ., Toxoplasma gondii, Dibothriocephalus latum, Spirometra spp ., Schistosoma spp ., Echinococcus canadensis, and Sarcoptes scabei var canis. Category 3 includes human infection where the zoonotic infection link is rare but has occasionally implicated dogs. This category includes SARS-CoV-2, Bordetella bronchiseptica, Mycobacterium spp ., Corynebacterium spp ., Coxiella burnetti, Helicobacter spp. , Campylobacter spp ., Brucella canis, Balantioides coli, Blastocystis hominis, Bacillus anthracis, Dipylidium caninum, Taenia spp ., Trichuris vulpis, Gnathostoma spp ., Thelazia spp ., Dirofilaria spp ., Onchocera lupi, Heterophyes heterophyes, Metagonimus spp. , Fasciolopsis buski, Ctenocephalides felis, Cheyletiella spp ., Otodectes cynotis , and Cochliomya homnivorax . Changes in human behavior and control of canine infection would reduce the public health importance of these zoonoses.