Among the undesirable consequences of climate change is the sharp increase in the population of ticks. These mites, when they bite, can transmit several potentially dangerous diseases that are becoming a growing public health problem and a threat to those who enjoy nature walks.
An international team of scientists working in France has achieved very encouraging results with a new vaccine that, according to tests on mice, would slow the spread of Lyme disease – or borreliosis – and probably other tick-borne infections, such as encephalitis or Congo and Crimean hemorrhagic fevers. The innovative strategy consists of acting against the microbiota (bacteria, viruses and fungi of an organism), in this case the tick, to neutralize the borrelia bacteria inside it. It is believed that this method could also be used to combat diseases transmitted by mosquitoes, such as malaria, Zika or dengue. It would be a spectacular advance.
"The concept of the antimicrobial vaccine is revolutionary because it changes the vaccination paradigms that have existed since Edward Jenner and Louis Pasteur discovered vaccines", assures La Vanguardia the director of the project, Alejandro Cabezas-Cruz, a veterinarian of Cuban origin . He does his research at the National Food, Environment and Labor Health Safety Agency (ANSES), on the campus of the Veterinary School in Alfort, a suburb of Paris.
A classic vaccine immunizes directly against a pathogen. The new one being tested against borreliosis acts against the vector – in this case the tick, but it could also be used against mosquitoes – by inducing a modification of the tick's microbiota. This causes the pathogen – borrelia – to stop developing. If the victim of the tick is vaccinated, when the latter bites and sucks the blood it also ingests the antibodies generated by the victim. Given that the tick needs to be attached to the skin for about 72 hours to transmit borreliosis, it is thought that this time is enough for the antibodies to act in the mite and stop infecting. If it bites another victim, it won't infect them either. The change in the microbiota of a mother tick is likely to be passed on to the offspring, so the offspring would not be infected either.
"Modern science has not succeeded in eradicating a disease transmitted by vectors", remembers Cabezas-Cruz. According to him, a massive fumigation against ticks "is problematic due to environmental pollution and because ticks generate resistance to acaricides, so they stop having an effect after a while".
The vaccine could take ten years to be available to the public, but exceptional circumstances would cause it to be accelerated, as it already happened with messenger RNA vaccines due to covid.
Ticks are not only a serious problem for people. They are also a major threat to livestock and, therefore, to food production, especially in developing countries. These mites transmit diseases to animals, such as babesiosis, anaplasmosis and theileriosis. "There are countries in Africa that cannot raise cattle because of the diseases transmitted by ticks," emphasizes Cabezas-Cruz.
Tick researchers are confident that in the future their discovery could lead to the vaccination of wild animals that are a reservoir of pathogens, and thus drastically reduce epidemics. Cabezas-Cruz points out that something similar is already being done, for example in Spain, with the wild boar population, which are a reservoir of tuberculosis. These animals are given food treated with the vaccine so that they stop spreading the disease. Now it's time for ticks and blood-sucking species.
Warming has extended the period of activity of ticks, which hibernate in the coldest months, and has favored their reproduction. Climate change has also influenced its geographical distribution. Its presence now includes more territories. Other factors may have influenced its proliferation, such as the presence of unharvested wood in forests or the strategy of expanding green areas in urban centres.
The Public Health of France (SPF) has revealed disturbing data about borreliosis. In 2009, 40 cases of the disease were detected for every 100,000 inhabitants. In 2020, it had increased to 90 cases per 100,000 inhabitants. Encephalitis infections caused by ticks exceed 30, on average, each year. Some of the diseases transmitted by ticks can give mild symptoms, similar to the flu, or digestive problems, but sometimes, if not treated in time or due to other circumstances, they evolve into serious cases and can even cause death.
