Controlling vector-borne diseases without borders
Vector-borne diseases (VBDs) account for more than 17 per cent of all infectious diseases in humans and put major pressure on the health of companion animals and livestock, resulting in billions of dollars lost annually.
Experts warn climate warming is providing ideal environmental conditions for vectors, which is impacting their distribution and the incidence of vector-borne diseases.
We take a look at three of the most prolific VBDs and the challenges they’re presenting.
Spread by phlebotomine sandflies, leishmaniosis infections are zoonotic and highly fatal to both dogs and humans if untreated. Dogs are the most important human reservoir , so ensuring the right preventative measures are taken, such as using parasite control collars, are key in helping to control the spread.
The disease is usually present in subtropical regions of the world, however the increased mobility of dogs from endemic areas through adoption and increased pet travel may introduce the disease to areas considered free from it. For example one strain, Leishmania infantum, was once restricted in areas around the Mediterranean, affecting an estimated 2.5 million dogs, but the disease has spread north and is now endemic in places it was not found before.
Rift Valley Fever
Taking its name from the valley in Kenya where it was first isolated, Rift Valley Fever (RVF) is a dangerous zoonotic disease that can be widely spread through two species of mosquitoes.
RVF has a devastating impact on rural communities in sub-Saharan Africa where it is mostly endemic. It affects large numbers of animals, including sheep, cattle and dogs, causing abortions in livestock and killing more than 90% of young animals.
Rift Valley Fever can jump to humans through interaction with livestock or mosquitos and cause fevers that, although less severe than those in animals, can cause encephalitis, blindness, haemorrhage and even death.
The concern is that, due to the presence of suitable RVF vectors in the US and Europe, the disease could spread rapidly if it reached these new territories where losses would be significant. It has already demonstrated its ability to move, following confirmed cases in Egypt, Saudi Arabia and Yemen.
Hope is on the horizon though as funding for RVF research increases. A research team at Oxford University is currently developing a RVF vaccine, which would be the first-ever vaccine for both human and animal use.
East Coast Fever
Approximately 50 million cattle are at risk of contracting East Coast Fever (ECF) and annual losses are estimated to be US$596m, according to GALVmed.
The tick-borne disease exists in sub-Saharan Africa but it has significant potential to spread through uncontrolled movement of animals due to the large presence of the tick vector and suitable habitats, while the vector has developed a resistance to some insecticides.
Although a vaccine exists, this strain is not always accessible for producers in the region. Research groups like the International Livestock Research Institute (ILRI) are working to improve distribution and develop new vaccine candidates.
The way forward
Eradicating these diseases is difficult, but effective parasite control of products in pets and livestock alongside management or vaccination programmes can help contain them.
Improving surveillance of VBDs will also help to discover changes in distribution early on, while imposing strict checks on animal movement will help limit vector movement.
Novel techniques are also being researched, such as genetically modifying insects to be resistant to certain types of viruses. Although this is currently targeted at human disease pathogens, as more people adopt a One Health approach it is hoped this will help the animal health sector progress too.
Read more about vector-borne diseases in our publication: The Growing Threat of Vector-Borne Disease in Humans and Animals.