Outfoxing Rabies, One Vaccine-Loaded Chicken Head at a Time

To mark the 10th World Rabies Day, Naturally Speaking’s Laurie Baker (@llbaker1707) steps out from her interviewer role to share how she and her collaborators at IBAHCM and the Friedrich Loeffler Institut (FLI), are using lessons from fox rabies elimination in Western Europe to outfox rabies. 

With Europe on the brink of World War II, the sudden appearance of rabies in foxes was the last thing on the minds of European veterinary authorities.  By the time they realised what was happening, it was too late. The epidemic had reared its ugly head and rabies was spreading through fox populations across Western and Central Europe.

Fox rabies on the move. Map showing the decadal spread of the European fox rabies epidemic over time from its beginnings in the 1940s. Courtesy of the FLI.

Rabies is a deadly viral infection that targets the brain and nervous system and is spread through the bite of an infected animal. Without immediate treatment the outlook is grim; nearly 100% of rabies victims die.

Rabies cycle in foxes. Foxes exhibit symptoms of rabies an average of 21 days after they are bitten as levels of the virus in the saliva increase. During the ~7 day infectious period they are able to pass on the virus, before they die from the disease.  Diagram courtesy of FLI.

The scourge of rabies is not new. Early records trace the disease back to Mesopotamia. Today, over 59,000 people die of rabies each year. Historically, people in Europe contracted rabies through dog bites, but this threat has been eliminated through vaccination of pets. The origin of fox rabies in Europe is still a matter of debate. While some scientists believe that the epidemic of fox rabies started south of Kaliningrad during World War II as a result of a sustained spill-over from dogs, recent studies have revealed the existence of similar rabies virus lineages in the Asian part of Russia, thus questioning this hypothesis. Whatever its origins, as the epidemic in foxes gained ground in the 1940s, it presented an entirely new threat to wildlife, domestic animals, and humans; one that required substantial changes in control policies.

In the late 1970s, European veterinary authorities were ready to launch a counterattack. Early attempts to contain rabies through fox culling failed. But they had hope in a new edible vaccine for foxes.  The new vaccine could prime a fox’s immune system providing protection from a future attack. However, developing an effective method for packaging and distributing the vaccines across vast areas for consumption by foxes presented a trickier challenge.

At first, the idea of dropping vaccine-loaded chicken heads from the sky seemed absurd.

How could they ensure that hundreds of thousands of foxes all over Europe would find and eat the vaccine? With careful study of fox behaviour and the use of the chemical marker, tetracyclin, which is detectable in fox teeth after consumption, the attack on rabies was ready to begin.

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Over the next three decades, vaccine-loaded chicken heads, later replaced by chocolate-bar resembling fishmeal baits, would rain down across Europe twice a year.  The result is one of the greatest vaccination success stories in wildlife to date. A little more than three decades on —with vaccines dropped over an area equal to more than 330,000 football pitches (2.36 million km2)—rabies was completely eliminated from nine countries in Western and Central Europe.

The unique history of this effort is recorded in the Rabies Bulletin Europe, a WHO database maintained by the Friedrich Loeffler Institut which contains detailed reports of rabies cases and European vaccination efforts. We are using these reports as a means to reconstruct a picture—using mathematical models—of how fox rabies spread through Europe and was effectively controlled by vaccination. More generally, our work looks at why infectious diseases persist and how vaccination can exploit a disease’s weaknesses. Our goal is to understand the key factors that made these vaccination air raids a success, and use this information to design future air raids to eliminate the disease.  This is critical because fox rabies continues to exist in large parts of Russia and Eastern Europe and has recently emerged in Turkey. If we fail to eliminate rabies in these areas, the spread of rabies will continue and could reinvade Western Europe, undoing decades of hard-won progress.

But eliminating a disease is not straightforward. Only two diseases have been successfully eliminated worldwide—smallpox and rinderpest (a disease in cattle)—despite costly global attempts to eliminate nine key infectious diseases. In practice, ridding an area of the last 10% of disease cases requires the same, if not more, effort than that used to eliminate the first 90% of cases. This is because in the final stages of elimination the behaviour of the disease often changes; it also becomes more difficult to detect a disease when it is reduced to low levels.

So how do we avoid a fate similar to that of Sisyphus, who was condemned to push a heavy boulder uphill for eternity, only for it to tumble back down when he was nearly at the top?

Thanks to advances in statistics, we now have the tools to study the patterns and understand the drivers of disease spread. This allows us to explore questions that will improve our ability to combat the disease: when and where should vaccines be dropped to be most effective? How does the landscape, such as mountains and rivers, direct or slow rabies spread? How does your neighbours’ strategy affect your ability to eliminate rabies in your region?

Diseases like rabies don’t respect borders—even as political uncertainties play out. Lessons learnt from mathematical models of the European rabies experience will be used in the war against rabies to improve the planning of ongoing vaccination air raids. But to defeat rabies, countries need to continue to work together and overcome their differences. Only with Europe united against the disease front, can rabies be outfoxed!western_europe_vac_cases_oct_2016Vaccines Away. Animation showing quarterly rabies cases and cumulative vaccination efforts from the previous 5 years in Western Europe from 1987-2006. Over 30 years, vaccines were dropped over an area equal to more than 330,000 football pitches (2.36 million sq. km). Blue polygons represent the vaccinated areas, with darker shades indicating areas vaccinated more than once, and red dots represent fox rabies cases. © IBAHCM.


Institute of Biodiversity, Animal Health & Comparative Medicine: Dr. Katie Hampson (@hampson_katie), Prof. Jason Matthiopolous (@JMatthiopoulos), and Micaela De La Puente Leon (@MicaDelaPuente).
Friedrich Loeffler Institut, Germany: Dr. Thomas Müller, Conrad Freuling, Patrick Wysocki and Ronald Schröder.

Interested in learning more about fox rabies? 

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