The Swiss Tropical and Public Health Institute, together with European and African collaborators, carried out a mass dog vaccination in Chad and determined its effect on human rabies exposure. The study employed a bio-mathematical method for estimating the transmission dynamics of rabies. The researchers conclude that with political will and the necessary funding, elimination of rabies is possible in Africa.
Rabies is a viral disease that kills tens of thousands of people every year, predominantly in Africa and Asia.The disease is transmitted through the bites of infected dogs and foxes. In Westand Central Europe, rabieswas eliminated some 20 years ago. Switzerland was declared free of rabies in 1999 after implementing astrategy targeting foxes.
"If you want to prevent humans from dying from rabies in Africa and Asia, you need to eliminate dog rabies,"said Jakob Zinsstag from the Swiss Tropical and Public Health Institute (Swiss TPH), first author and principalinvestigator of a study in Science Translational Medicine. Swiss TPH, together with collaborators in Europeand in Africa, demonstrated the proof-of-concept that elimination of rabies is feasible. "We have shown thatAfrican teams in one of the poorest countries can eliminate human rabies through mass vaccination of dogs.What is needed next is additional funding and a concerted political will," said Zinsstag, an epidemiologist andveterinary public health expert.
The investigation was carried out in N’Djamena, the capital of Chad where 1.1 million people live alongsidesome 30,000 dogs. In 2012 and 2013, 20,000 dogs were vaccinated each year against rabies. Hence, morethan 65% of the city’s estimated dog population participated in the intervention, "an excellent coverage rate,"said Zinsstag. "We mobilised the neighbourhood chiefs and they in turn mobilised the people and their dogs."
A Model African-European Collaboration
Swiss TPH is a world-leading institute in the field of human and animal health - increasingly known as "OneHealth" - and maintains a productive collaboration with Chad dating back to the 1990s. Swiss TPH collaboratedwith a public-private partnership in Chad, namely the Centre de Support en Santé Internationale (CSSI) andthe Institut de recherche en élevage pour le développement (IRED). An additional player was the LaboratoireCentral Vétérinaire (LCV) in Bamako, Mali.
For the genetic analyses of collected rabies viruses, Swiss TPH was supported by the ETH Zurich in Basel,Switzerland, and by the Institut Pasteur in Paris, France. At Swiss TPH, an interdisciplinary team was establishedwith expertise in molecular diagnostics, mathematical modelling and veterinary epidemiology. "Themathematical modelling shows that the reproductive number, that is the number of secondary infections forone rabies-infected dog, fell under one, hence transmission is interrupted, and a molecular analysis shows thatthe circulating strains disappear," said Zinsstag and Nakul Chitnis, a co-investigator at Swiss TPH.
Further Insights through Phylodynamics
The study is one of the first research projects to apply a rigorous phylodynamic method to dog rabies, andhence, it expands upon the normative phylogenetics (i.e. assessing the genetic relatedness of virus strains)with the dynamics of transmission over time. This made it possible to calculate the reproductive number ofrabies among the dogs after the first mass dog vaccination in 2012.
"Dog rabies was likely re-introduced through the import of dogs by humans from outside N’Djamena after therabies elimination had been achieved," Zinsstag explains. The phylogenetic analysis supports this finding,since the sequence of nucleoprotein of the new viruses showed a different genetic structure. "The molecularmethod ascertained the results put forth by the mathematical model through an independent approach," said Zinsstag. "Therefore eliminating rabies is not a technical problem, but a matter of political will and sufficientfinancial resources."
The Swiss TPH study was financially supported by the UBS Optimus Foundation in Switzerland (vaccine, epidemiologicalfield work and laboratory investigations). The Chadian government covered other costs (logisticsand personnel).
Towards Elimination of Rabies in Central and West Africa
Eliminating dog mediated human rabies by 2030 is part of the Sustainable Development Goals (SDGs). "It willbe a formidable challenge to reach this SDG goal by then, but we can prevent people from dying from dogtransmittedrabies," said Zinsstag. "Our study provides an important proof-of-concept for the Global Alliance forRabies Control (GARC) and the Pan-african Rabies Control Network (PARACON) that rabies elimination inAfrica indeed can be achieved."
As a next step, Swiss TPH and its partners plan to extend mass dog vaccination against rabies across Chad."We have calculated that with 28 million euros, it would be possible to eliminate rabies throughout the country.However, an important challenge is migration: once Chad is free from rabies, the disease might be re-importedfrom neighbouring countries such as Cameroon and Sudan. We therefore need a concerted Pan Central andWest African approach, led by the Economic Unity of West African States ECOWAS and the African Union.This would bring along the additional benefit of promoting peace through cooperation." Zinsstag estimates thatin order to free Central and West Africa from rabies, the costs would amount to around 1 billion euro over a 20-year period.
One Health Rabies Research at Swiss TPH
Swiss TPH maintains a West African research network in the field of human and animal health based on anexcellent collaboration with many African partners, such as CSSI in Chad and the Centre Suisse de RecherchesScientifiques en Côte d’Ivoire (CSRS), among others. Swiss TPH pursues a two-pronged approach with theoverall aim of eliminating rabies in humans: eliminating dog rabies and making post-exposition prophylaxisaccessible to all people in West and Central Africa. For this last approach, Swiss TPH collaborates with theGlobal Vaccine Alliance (GAVI).
One Health is, in Zinsstag’s own words, the "added value of a close collaboration of human and animal health.If medical experts and veterinarians work together more closely, they can improve health to a greater extentthan they could alone." The concept of One Health was instigated by the veterinary epidemiologist Calvin W.Schwabe in the 1960s. Swiss TPH has developed the scientific theory behind it as well as the associatedPage 3teaching and training. For instance, Swiss TPH developed the first massive open online course (MOOC) inOne Health, which is now being offered in its second year.