Essay: Animal and Human Health in the Tropics

Protecting Animals – Protecting Public Health

The rate of pet ownership is increasing globally as more people come to realize and appreciate the benefits of animal companionship. But pets can carry diseases that may spread between them and humans – either directly or indirectly, through fecal contamination of soil and water or through vectors such as ticks, fleas or sandflies. Therefore, good animal health contributes to public health – and effective parasite protection for pets can help save lives. However, in the tropics, some zoonotic diseases are neglected because they lack funding for crucial research and resources for their control. This leads to a gap in our knowledge about the significance and distribution of clinically important parasitic diseases of dogs and cats in much of this region. An expert group is on a mission to address this gap by supporting pet owners and veterinarians with information and guidelines on how best to diagnose, treat and prevent these diseases.

Pet ownership is increasing worldwide, with dogs and cats among the most popular choices.


Only a century ago throughout the world, many people lived closely together with their farm animals – sometimes even under the same roof. Getting up in the morning to feed them, farmers always needed to wake and work in unison with their animals – be it sheep, cattle, chickens or goats. Cats and dogs also accompanied peoples' daily work routines, whether catching mice or protecting a territory from strangers. 


Today, many people in countrysides and cities alike still enjoy the company of pets such as cats and dogs. Having a pet is even good for human health: spending time with pets can lower stress levels and benefit cardiovascular health. For example, dog owners benefit by going for walks with their pets regularly. Some studies even suggest that cat ownership can decrease the risk of heart attacks and stroke[1]. Many children have their own animal friend to take care of, which helps them learn responsibility. For all of these reasons, it’s no wonder that pet ownership is growing around the world and that pets are increasingly considered as part of the family. 


Dr. Filipe Dantas-Torres, Laboratory of Immunoparasitology, Department of Immunology, Aggeu Magalhães Institute (Fiocruz), Brazil – and Founding Director & Scientific Coordinator of the Tropical Council for Companion Animal Parasites (TroCCAP)

One could conclude that pet ownership is a growing global trend. But there are strong regional differences – based on the environment, culture and climate conditions. Similarly, depending on the geographic location in which dogs or cats reside, their parasites and diseases can be significantly different from one region to the other. Some of the diseases are zoonotic – meaning they can infect both animals and humans, through the ingestion or contact with infective stages of parasites harbored by pets, as well as the bite or sting of a vector such as a flea, tick or sandfly. So if animals are infected, public health can be threatened, too.


Cat ownership also provides benefits, with studies finding that our feline friends can decrease the risk of heart attack and stroke. For children, cats provide good companionship and the opportunity to learn responsibility.

As a part of responsible pet ownership, animals should be brought to veterinarians for regular health check-ups, which should include ensuring that they are up-to-date with vaccinations and effectively protected from parasites.



Pet Ownership in the Tropics

The tropics are unique, covering a massive area and a variety of landscapes. With regions spanning from Southeast Asia, the Pacific Islands, Northern Australia, South Asia (including India), Africa, Latin America and the Caribbean, the tropics experience everything from hot, humid weather to seasonally dry zones. Mountainous and less arid zones also characterize this region. Such diverse conditions also support a diverse range of pathogens and vectors.


In the tropics, the co-existence of true companion animals with semi-domestic and community animals complicate the fight against parasites.



In these regions, the dog and cat populations are far from comparable to Europe or North America. In the United States, the majority of Europe and in Australia, legislation promoting responsible pet ownership assures that the majority of companion animals are indeed ‘pets.’ Regular veterinary check-ups for pets are considered a normal responsibility of pet ownership. In contrast, three quarters of the dog population in developing regions of the tropics may be classified as free-roaming community or semi-domesticated dogs. These animals contaminate the environment with excreta that are a source of parasite eggs and larvae capable of infecting pet dogs and humans. 


Pet ownership in tropical countries is on the rise. In Malaysia and Vietnam, dog populations have increased by seven percent and nine percent, while cat population by two percent and five percent in the past five years alone[2]. According to The Brazilian Institute of Geography and Statistics (IBGE), Brazilians have more than 52 million dogs, which exceeds the number of children under 14 years.


Associate Professor Dr. Rebecca Traub with Melbourne Veterinary School, University of Melbourne in Victoria, Australia – and Founding Director & Executive Secretary of the Tropical Council for Companion Animal Parasites (TroCCAP)



In the tropics, the co-existence of true companion animals with semi-domestic and community animals contributes to the challenge of parasite control programs. Families owning dogs or cats in the tropics often lack information about the risk of zoonotic parasites and may also have limited financial resources to seek veterinary advise or implement regular parasite control. In addition, veterinary awareness and treatment of pets may be lacking, too. This is especially a huge problem in developing countries, as uncontrolled and untreated dog and cat populations coupled with poor sanitation can lead to heavily contaminated environments. Contaminated environments, especially in the direct surroundings of houses and villages, increase the exposure and likelihood of infection, especially for children.



Neglected Zoonotic Diseases – a Threat for Public Health

“Animals play a very important role in neglected tropical diseases – since there are a lot of zoonotic diseases between humans and animals. If we are fighting against neglected tropical diseases – to effectively control or eradicate them – we have to see beyond human beings only. And we have to take animals, or whatever the host is, as well as any vectors into the equation as well.”

Professor Dr. Norbert Mencke, Global Head of Policy & Stakeholder Affairs with Animal Health at Bayer


Many canine and feline parasites cause zoonoses, including species of Toxocara (dog roundworm), Ancylostoma (hookworm) and Echinococcus (tapeworm)The World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO) and the World Organisation for Animal Health (OIE) recognize the diseases caused by these parasites as “neglected zoonotic diseases.” Of WHO’s list of 17 neglected tropical diseases (NTDs), eleven are parasitic in nature. For example, ‘Soil Transmitted Helminths’ and the vector-borne leishmaniasis are good examples of NTDs that need to be tackled through a ‘One Health’ approach: Their strategic control requires the application of integrated multidisciplinary input involving veterinarians for the animal part, physicians for the human side of the diseases, as well as public health practitioners including the environmental and vector-control aspects.


If animals are infected with a zoonotic disease, public health can be threatened, too.


Both the European Scientific Council of Companion Animal Parasites (ESCCAP) and the Companion Animal Parasite Council (CAPC) in the United States are independent, non-profit organizations consisting of experts in the field of parasitology and public health from across Europe and the United States, respectively. Initially convened in 2002 (CAPC) and 2005 (ESCCAP), the role of these organizations is to develop recommendations for the optimal treatment and control of companion animal parasites, with the aim of protecting the health of pets and the health of the public, by reducing the risk of zoonotic parasite transmission. Their websites comprehensively present the life cycles, diseases, diagnosis, control, prevalence and distribution maps of a wide variety of internal and external parasites of dogs and cats. The guidelines aim to increase awareness and inform practicing veterinarians and public health professionals of the most relevant parasites within each region and provide specific guidance for best practice procedures to protect pets and the public from parasitic infections.



“One health means the recognition that human beings are not alone; we are part of the whole. We have left behind our old, anthropocentric view that human health is not linked to animal and environmental health.”

Dr. Filipe Dantas-Torres, Laboratory of Immunoparasitology, Department of Immunology, Aggeu Magalhães Institute (Fiocruz), Brazil




However, recommendations vary according to country, and in much of the tropics, resources to fund studies addressing these issues are still limited. For some parasites that are restricted in geographical distribution, knowledge about their impact as veterinary or human disease relies largely on local research and knowledge. The prevalence of these parasites may depend solely on the distribution of region-specific intermediate hosts, the vectors transmitting the parasite, the density of parasite and vector species, the density of humans and animals and certainly the interdependencies between vector and hosts. Further, the prevalence is strongly influenced by sylvatic factors or anthroponotic behaviors. Therefore, more specific guidelines are required for their diagnosis and control. For example, in areas where Dioctophyme renale, the giant kidney worm of dogs, is endemic (including South America, China and parts of Southeast Asia), patients may not be appropriately diagnosed or treated if veterinarians fail to consider the parasite as a differential cause of chronic dysuria and haematuria and, occasionally, peritonitis.


“Communication is key to making a difference in addressing public health topics which affect real lives – of people and of animals. It helps stimulate partnerships and collaboration, which is the best premise to fight for better lives.”

Janice Chow, Global Communications Manager with Animal Health at Bayer


Soil transmitted helminths hookworm and roundworm are no exception. Zoonotic ancylostomiasis caused by Ancylostoma ceylanicum, a highly prevalent hookworm of dogs in the Asia Pacific, is now recognized as the second most common hookworm infecting humans in socioeconomically disadvantaged communities in the region. Larvae of this hookworm infect humans by penetration of skin, most commonly the feet and buttocks. If untreated, this hookworm may cause diarrhea, severe abdominal pain and anemia. Toxocariasis is also an important zoonosis caused by the globally prevalent parasite Toxocara spp. It may manifest as visceral larva migrans, ocular larva migrans or as non-specific, mild symptoms referred to as ‘covert’ or ‘common’ toxocariasis. Studies revealed that toxocariasis is most prevalent among children from socio-economically disadvantaged populations – especially those within the tropics.


Leishmaniasis – a Deadly Disease

Of companion vector-borne diseases, leishmaniasis is one of the most serious. The first recorded cases of leishmaniasis occurred 4,000 years ago, and were found in the mummies of Ancient Egypt. Leishmaniasis is spread by infected sandflies, and dogs as well as humans can become infected. The disease is particularly insidious because its incubation period ranges from several months to several years. More than half of all infected dogs show no visible signs, and the disease may not be detected unless owners take their animals to a veterinarian who is well-informed of the occurrence of pathogens in the area. If signs occur, dogs may show skin lesions, which can be severe, as well as fever, weight loss and weakness, among other signs that may be easily confounded with other vector-borne diseases. Untreated, the disease often leads to death, and even treated animals remain infected for life and risk relapses. 


The organization TroCCAP works in close collaboration with practicing veterinarians, medical and public health professionals, regional governments and non-profit organizations. In addition to biannual meetings, the Council is highly engaged in capacity building, while organizing veterinary and public outreach events in each region to facilitate transfer of knowledge through local lectures, workshops, symposia within local conferences and webinars to primary stakeholders such as veterinarians and breeders. 


Working Towards a Solution

The Tropical Council for Companion Animal Parasites (TroCCAP) is a group of regional (e.g. Asia-Pacific, Latin America and Caribbean, and Africa) experts consisting of, veterinary clinicians, parasitologists, physicians and allied industry partners. The group collaborates to inform, guide and make best-practice recommendations for the diagnosis, treatment and control of companion animal parasites in the tropics, with the aim of protecting animal and human health. TroCCAP has already achieved its first goal, the publication of a guideline for canine endoparasites, with a feline guideline underway. 



In Europe and the United States there is 1 dog or cat to every 3 - 4 households. In contrast, 3/4 of the dog population in developing regions of the tropics may be classified as free-roaming community dogs.

This figure may equate to as high as 1 dog to every 5 people in Kathmandu, Nepal, and Bali, Indonesia; 1 dog to every 4 people in the Philippines and Bolivia; and 1 dog to every 3 people in rural Mexico. [3]



The past decade has seen a moderate increase in published research literature associated with companion animal parasites in tropical countries. With further research and public-private commitment, there is hope that further progress for human and animal lives in the tropics can be achieved.



[1] Qureshi, A. I., Memon, M. Z., Vazquez, G., & Suri, M. F. K. Cat ownership and the risk of fatal cardiovascular diseases. Results from the second national health and nutrition examination study mortality follow-up study. J. Vascular & Interventional Neurol. 2, 132–135 (2009).

[2] Bayer consolidated data from various sources

[3] AVMA, 2012; fediaf, 2010     

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