A new disease –Lyme- is one of the fastest growing vector-borne diseases in the Western world – the threat it poses has become increasingly apparent in recent years. Estimates suggest that more than 300,000 people are diagnosed with the disease each year in the US and more than 65,000 cases a year are diagnosed in Europe. However, the true number of people affected is probably underestimated due to under-reporting and the limitations of current diagnostic tests.
On any ranked list of nasty diseases transmitted by mosquitoes, ticks and fleas in the Western world, Borrelia burgdorferi, would have to lie near the top. These bacteria cause Lyme disease, which was first recognised in the US in the early 1970s among patients in Lyme, Connecticut. However, the oldest known case was the Tyrolean Iceman, a 5,300-year-old Copper-age mummified individual, discovered in the Italian Alps.
Borrelia burgdorferi is a spirochete (corkscrew-shaped bacterium) that consists of more than 20 sub-species, five of which can cause disease in humans.Borrelia can flourish inside the tick, where they migrate from the gut to the saliva glands. In this way, they can penetrate human skin when a tick takes a blood meal and disseminate via the blood to multiple tissues. To survive and establish infection, Borrelia mutates in a number of ways to become invisible to the host’s immune system.
The main vector for transmitting the bacteria in Europe is the deer tick, Ixodes ricinus, but other Ixodes species act as vectors in the US and in Asia. Humans can become infected after being bitten by an infected tick. However, as Ixodes ticks can also transmit other pathogenic bacteria and viruses, it can be hard to diagnose Lyme disease among the potentially large number of infections that may have been contracted as a result of the tick bite, meaning it often goes untreated.
But it’s not just ticks we have to worry about. Lice, fleas, and mosquitoes have also been found to contain Borrelia. Worrying, Borrelia bacteria may also be transmittedfrom person to person through saliva, organ transplants, blood transfusions, sexual contact or breast milk. It has also been suggested that Lyme disease could be transferred to a foetus via the placenta, however this has yet to be proven.