Unfortunately, setting your priorities isn’t always easy – especially when thousands of lives depend on your decisions.  In the world of diseases, deciding which illness to address first can prove crucial to a country’s future.  However, agreeing on the actual decision is actually the last step in disease prioritization.  Disease experts recognize that health isn’t limited to one area; what affects one country may have repercussions in another.  Evidently, prioritization isn’t just a way of choosing what you should do first.  It is a debate over what yields the most harm currently, and why solving it will yield the most benefit for a region and surrounding areas; it is a way of selecting the best option in the presence of many, given a finite amount of resources (Brookes, Del Rio Vilas, & Ward, 2015).

A significant amount of focus lies on animal-borne illnesses.  Infectious diseases don’t always come from humans – in fact, nearly three-quarters of them originate from wildlife, particularly from wild animals (“Setting Priorities,” 2017).  Such illnesses are known as zoonotic diseases, or zoonoses, indicating that they are transmissible from animals to humans.  Zoonoses cause about 20% of all human illnesses and deaths in poorly developed countries, leading to a shocking 2.4 billion cases of human afflictions per year (Rist, Arriola, & Rubin, 2014).

Fighting zoonoses and other infectious diseases requires many assets: a large workforce, surveillance technology, laboratory capacity, and sufficient funds are just a few of the necessary means.  These are needed to effectively improve health response rates to outbreaks and disease control tactics (Rist, Arriola, & Rubin, 2014).  As a result, disease prioritization is a difficult but much needed task, because it allows health leaders to focus these limited resources in a way that will yield the greatest advancements in these areas.

So then, the question arises: how can you get an entire group of health experts to agree that a few zoonotic diseases are more important than all the others?

The CDC has recently used a remarkable, proposed prioritization mechanism that facilitates the tedious process.  Dubbed the One Health Zoonotic Disease Prioritization Tool (OHZDP Tool), it consists of a five-step process and utilizes an Excel spreadsheet.  To use it successfully, this tool has its own complexities that health workers must sort out.  I was able to talk to Cassidy Rist, an assistant professor at the Virginia-Maryland College of Veterinary Medicine, who was a key developer of the OHZDP Tool.

The first step of using this tool is essentially group work.  The members should be knowledgeable representatives from different health sectors, such as vets, bacterial pathologists, etc.  The goal of the group is to create a list of what the experts believe are the most important diseases.

When I asked Rist how to go about this, she explained that making the list is actually easier than one would imagine.  She stated, “It generally is not that difficult for groups to agree on it, because you’re not limited.  You can make the list as long as you want to accommodate the interests of the group and the prioritization exercise itself.”  She added, “There are lots of reason that diseases will get on list, and those reasons are based on the purpose of the usage of the list.  If the purpose was to develop a new vaccine, then you wouldn’t put diseases that already have vaccines.”

The second step is simpler: developing the criteria to rank the diseases.  The criteria can include aspects such as epidemic potential, bioterrorism potential, mortality rate, and economic impact.

Step three is perhaps the most difficult, and requires the most teamwork.  The group has to develop a question for each criterion – but even the questions need to meet specific requirements.  Firstly, they must have either binomial answers, as in “Yes/No,” or multiple answers that involve percentages (Rist, Arriola, & Rubin, 2014).  These questions can be modified according to the purpose of the prioritization.

Ranking the criteria is the fourth step.  This utilizes an already existing ranking process called the Analytic Hierarchy Process (AHP), programmed into a Microsoft Excel Spreadsheet.  Each group member first individually ranks the criteria, and the program merges everyone’s responses.  This results in a ranked list of criteria, denoted by numerical weights; 5 means highest rank, 4 is second highest, etc.

The fifth and final step is to rank the zoonoses.  In order to accomplish this, the Excel program ranks the diseases according to responses to the group-generated questions.  A bit of arithmetic is involved: scores are assigned to each answer.  If the answer was binomial, “Yes” has a score of 1 and “No” has a score of 0.  If multinomial, the score is calculated by dividing the answer’s ordinal position by the number of answers to the question (e.g. if “< 10%” is the first answer out of four, the score is ¼ = 0.25) (Rist, Arriola, & Rubin, 2014).  The scores for all questions are then summed up, compared to the highest score, and normalized.  This creates the final list of ranked diseases.

The beauty of the tool, as Rist describes, is its objective and definitive nature.  “The tool prevents people from arguing about a specific disease.  You can’t play favorites, like “I worked on E. coli so I think this should be ranked in this place” – individuals can’t make those decisions.  They can only go through weighting the criteria, and results come out in this way that is transparent and people can see how the diseases were ranked as they were.  You can discuss the final list, but you can’t argue with the way it came out.”

Thirty years from now, the world population will be around 9.7 billion (“Global Disease Outbreaks,” n.d.).  More people will need adequate health services.  In countries where animal agriculture remains prominent, people will no longer be able to maintain a safe distance from potentially sick livestock (“Global Disease Outbreaks,” n.d.).  And, above all, infectious diseases will be able to thrive even more than they do now.  The OHZDP Tool offers an impartial, efficient way to help future leaders decide which disease will, given allocations, predominantly enhance public health.  It embraces a “multi-sectoral approach” to improve disease prevention and control, and provides flexibility to national governments on what they want the tool to accomplish (Rist, Arriola, & Rubin, 2014).  Prioritization is still an undeniably complex process, but luckily this mechanism provides some stress relief.

Recently, the CDC has used the OHZDP Tool in Kenya, Azerbaijan, and South Africa, though Rist does not know much about the tangible outcomes.   “But,” she notes, “Countries like it, and the CDC likes the outcomes they’re getting.  There will be a paper coming out that takes results of the workshops and compares them across different countries.  Right now, though, it seems to be effective in its goal of bringing human and animal health together in zoonotic diseases.”


Arriola, C. S., Rist, C. L., & Rubin, C. (2014). Prioritizing Zoonoses: A Proposed One Health Tool for Collaborative Decision-Making. PLoS ONE 9(10). http://dx.doi.org/10.1371/journal.pone.0109986

Brookes, V. J., Del Rio Vilas, V. J., & Ward, M. P. (2015). Disease Prioritization: what is the state of the art? Epidemiology & Infection, 143(14), 2911-2922.  https://doi.org/10.1017/S0950268815000801

“Global Disease Outbreaks.” (2016). Global Risks Report 2016, 11, 64-72. Retrieved from http://www3.weforum.org/docs/GRR/WEF_GRR16.pdf

Rist, Cassidy. (2017). Setting Priorities for Global Disease Surveillance, Preparedness and Response [PowerPoint slides].  Retrieved from https://blackboard.jhu.edu/bbcswebdav/pid-3954147dt-content-rid-16720737_2/courses/AS.280.228.11.IN17/JHU_2017%20Winter%20Intersession_MONDAY.pdf

Posted by Alice Kuan

Alice is a freshman pursuing a Public Health and Economics double major and a Psychology minor. As a marketer for HMR, she serves as the liaison between HMR and other student organizations and helps plan fundraisers. She is also a reporter on the HMR Global Health Team. At Hopkins, Alice serves on the Executive Committee of Public Health Student Forum, hosts a semesterly health fair in the Baltimore East Oliver Neighborhood, and tutors children from Baltimore City public schools. She is also an avid cellist and plays with the Hopkins Symphony, as well as small ensembles at the Peabody Institute. Outside of campus, she does research for a maternal and child health initiative that focuses on chronic diseases and gaps in treatment. Recognizing that funding is vital to public health, Alice hopes to shape her career as a health economist to help health institutions make well-informed financial decisions.

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