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Institute of Medicine (US) Forum on Microbial Threats. The Causes and Impacts of Neglected Tropical and Zoonotic Diseases: Opportunities for Integrated Intervention Strategies. Washington (DC): National Academies Press (US); 2011.

Cover of The Causes and Impacts of Neglected Tropical and Zoonotic Diseases

The Causes and Impacts of Neglected Tropical and Zoonotic Diseases: Opportunities for Integrated Intervention Strategies.

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College of Veterinary Medicine, Ohio State University

Animals and people often live close together throughout the developing world. People are especially dependent on livestock and poultry for food, clothing, fertilizer, draught power, and an important degree of financial security. At the same time, these animals and their products create disease risks for the populations who most depend on them.

A zoonosis is an infectious disease that can be transmitted from an animal to humans. The transmission may be direct such as with rabies or indirect through either vectors such as ticks and mosquitoes (trypanosomiasis) or through food, water, or soil (helminths). A neglected zoonotic disease (NZD) is a zoonosis that is commonly associated with poverty and impacts the lives and livelihoods of millions of poor livestock keepers or those living in periurban slums primarily in developing countries. Some NZDs are part of existing lists of neglected tropical diseases (NTDs) or comprise their own list but all share similar characteristics and attributes.

A key characteristic of NZDs is that they are closely associated with poverty and they disproportionately affect neglected populations. Poor people are more at risk of contracting many zoonoses. For example, anthrax, bovine tuberculosis, and brucellosis are primarily occupational diseases, and small livestock producers worldwide are at risk and more frequently acquire these infections from their animals. The Food and Agriculture Organization estimates that, globally, there are between 500 million and 900 million food-insecure livestock keepers, and livestock contributes to the livelihoods of 70 percent of the world's rural poor (WHO et al., 2006). The poor are also more vulnerable to diseases associated with consumption of livestock products and are at risk for zoonotic diseases such as cysticercosis and other parasitic and food-borne illnesses. In addition, vectors, water, and the environment can also be sources of NZDs. Once infected, it is the poor that are least likely to get proper medical care. The impact of NZDs is also worse in poor households where a dual burden is borne because both people and their animals are involved. Thus, NZDs not only make members of families ill, but also at the same time, limit the productivity of their livestock and poultry and, thus, take away the funds that would be used for emergencies, their family's well-being, and funds used to cope with these illnesses.

As our world grows progressively interdependent and the populations of people, domestic animals, wildlife, and animal products also increase and expand globally, we can expect more interactions among these groups and certainly the era of emerging and reemerging zoonoses will also expand and grow proportionately (Tomley and Shirley, 2009). As the human–animal interfaces intensify and accelerate, there is a growing concern with the emergence and reemergence of more zoonoses and animal-associated diseases, including leptospirosis, leishmaniasis, Q fever, toxoplasmosis, anaplasmosis, food-borne trematodes, ehrlichia, bartonella, Chagas disease, and toxocariasis. Although most of these diseases can be considered in the category of neglected diseases and are increasingly associated with slums and periurban locations, some of these diseases are also found in developed countries because of the relocation of human populations, global travel, and the movement of food and animal products as part of the rapidly expanding global food system.

Of the 27 infectious diseases tracked by disability-adjusted life-years by the World Health Organization (WHO), 20 are classified as zoonotic and 7 others show that animal transmission cycles are important considerations (WHO et al., 2006). Thus, understanding these diseases by viewing them through the lens of animal health and veterinary medicine not only gives us a different perspective but also reveals new potential intervention strategies to reduce the significant burden of this group of diseases.

With the exception of zoonotic trypanosomiasis, which is restricted to parts of Africa, the rest of these zoonoses are found worldwide. The significance of neglected zoonoses is expanding, and their health and socioeconomic impacts are increasingly being experienced by many countries, particularly in the developing world. The prevention and control of this group of diseases has proven especially difficult ,and they continue to further burden public health systems as well as to undermine efforts to improve and expand livestock production and exports (WHO, 2010).

The morbidity and mortality of NZDs are difficult to assess. Many of the NZDs may be difficult to diagnose, may be found in poor communities lacking surveillance or adequate medical or veterinary care, and are both under-reported and underappreciated. Yet we do know that toxocara infections may produce asthma in addition to visceral and ocular migrans; Chagas disease can result in severe heart disease, especially in Hispanics; cystocercosis, the pork tapeworm, is now considered the leading cause of epilepsy among Hispanics; ascariasis is a helminth that is a leading cause of impaired child development; and strongyloides also leads to developmental impairment, especially in immune-compromised patients. Rabies is responsible for an estimated 50,000 to 60,000 deaths each year, and children are disproportionally impacted. The cost of rabies is substantial considering that approximately 10 million people received postexposure prophylaxis annually (CDC, 2009). Finally, like other NTDs, many of the NZDs impact personal health and productivity over an entire lifetime and result in chronic disease conditions. In some rural locations, they may significantly reduce the labor pool of agricultural workers in the very communities where their work is most critical.

There is a compelling case to address NZDs worldwide based on moral consideration, human rights, economic impact, global health, and the reduction of pain and suffering in both human and animal populations. NZDs have a dual burden because they can be devastating to both public health and animal health and the most vulnerable people are the millions of poor livestock keepers found globally.

With the expansion of occurrences and increased socioeconomic and health impacts of NZDs, a new paradigm to address this group of diseases must emerge. We can no longer view these diseases as individual crises in agriculture that are disconnected from public health authorities and programs. Rather, there is now a need to design and implement integrated responses for these diseases that cross species lines and health communities. This makes medical and epidemiological sense because many of these diseases are concentrated in remote rural areas or in urban slums, and interventions can be focused accordingly. Those afflicted with NZDs commonly have co-infections as well, so the treatment of multiple diseases in individuals may represent only a marginal cost increase and, thus, very favorable cost-benefit considerations.

The principal concern with NZDs is that these diseases have divided constituencies and authorities. There is a critical gap between public health needs and veterinary responsibilities. Government authorities are often slow to respond and may be perceived to be in competition for limited funds. For NZDs, the risk of human health is understood; yet the most effective control route is usually via the infected animals (WHO Department of Food Safety, Zoonoses, and Foodborne Diseases, 2009). Thus, investments in animal health and veterinary infrastructure can have a dual benefit for improving both human and animal health. We now recognize that most emerging and reemerging pathogens are zoonotic and that these microbes readily move across a continuum between species, seeking new niches for survival. In today's complex and interconnected world, the microbes will continue to have unprecedented opportunities to readily move across species, find new niches and hosts, and remain as significant threats to our health and economic well-being as they have for centuries past. It is time to shift our attention “upstream” and focus our prevention and interventions at the origins of these diseases. Certainly, there is new hope, and progress in attacking NTDs that needs to include the NZDs.

NZDs lack critical research and policy support, and as governments and nongovernmental organizations take on greater roles in global health, they lag behind. Eric Fèvre stated, “While malaria is undoubtedly a very serious health issue, its over-diagnosis hides other problems. To compound this, people in marginalized communities can easily fall off the policy radar—many may be born, live and die without official record being made of them and, as such, they have a weak, or nonexistent, political voice. Thus, while these diseases are grouped as ‘neglected zoonotic diseases,’ it would be equally correct to identify them as ‘diseases of neglected populations’ (Doble and Fèvre, 2010). Unfortunately, the severity of health and socioeconomic impacts of NZDs remain unclear. Surveillance, diagnostics, interventions, training, program delivery, and integrated health planning still continue to be done separately with regard to public and animal health. Yet an integrated “One Health” focus and strategy would result in more diseases being prevented and/or treated in more cost-effective methods, and not only would lives be improved and saved for both animals and people, but we would also create a new opportunity to help alleviate poverty and achieve the key Millennium Development Goals of eradicating poverty and hunger, reducing child mortality, and combating diseases.

One Health is defined as the collaborative effort of multiple disciplines— working locally, nationally, and globally—to attain optimal health for people, animals, and our environment (AVMA One Health Task Force, 2009). As the lives of billions of animals, people, and products converge globally in an unprecedented biological mixing bowl that is embedded in rapidly changing ecosystems, the world of zoonoses is getting more attention. One Health teams and strategies must be created and implemented as integrated strategies to prevent and reduce disease, especially those focusing on the millions of impoverished people who depend on livestock and poultry for their livelihoods. The wonderful progress to reduce and eliminate NTDs such as river blindess, lymphatic filariasis, trachoma, and Guinea worm demonstrate that NTDs can be successfully addressed. However, it is time to implement new frameworks to address NZDs and their global burdens, with a special emphasis on integrative and collaborative programs and with the same focus, energy, political will, and resources used to reduce these other NTDs. If not, the 21st century will continue to exclude those in need and their animal populations that also need care, support, and attention to improve their health. Improving animal health is now an important strategy for improving human health, and reducing the burdens of NZDs and other zoonoses is key to helping to helping to alleviate poverty.


  1. AVMA (American Veterinary Medical Association) One Health Task Force. One health: A new professional imperative. Schaumburg, IL: AVMA; 2009.
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  7. WHO; U.K. Department for International Development Animal Health Programme; Food and Agriculture Organization of the United Nations; World Organisation for Animal Health. The control of neglected zoonotic diseases: A route to poverty alleviation. Report of a joint WHO/DFID-AHP meeting; September 20 and 21, 2005; WHO headquarters, Geneva, with the participation of FAO and OIE. Geneva: WHO; 2006.
Copyright © 2011, National Academy of Sciences.
Bookshelf ID: NBK62511


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