Among the undesirable consequences of climate change is the sharp increase in the tick population. These mites, when bitten, 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 in mice, would stop the spread of Lyme disease - or borreliosis - and, probably, other infections due to ticks, 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 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 breaks with the vaccination paradigms that have been in place since Edward Jenner and Louis Pasteur discovered vaccines,” project director Alejandro Cabezas-Cruz, a Cuban-born veterinarian, told La Vanguardia. He conducts his research at the National Agency for Health, Food, Environment and Work Safety (Anses), on the campus of the Alfort Veterinary School, a suburb of Paris.
A classic vaccine immunizes directly against a pathogen. The new one that is being tested against borreliosis acts against the vector – in this case the tick, but it could do so against mosquitoes – by inducing a modification of the tick microbiota. This causes the pathogen – the borrelia – to stop developing. If the tick victim is vaccinated, when the tick bites and sucks blood, it also ingests the antibodies generated by the victim. Since 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 on the mite and stop infecting. If it stings another victim, it won't sting either. It is likely that the change in the microbiota of a mother tick is transmitted to the pups, so they would not be contagious.
“Modern science has not been able to eradicate a vector-borne disease,” recalls Cabezas-Cruz. According to him, a massive fumigation against ticks "is problematic due to environmental contamination 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 speed it up, as has 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 thus 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 due to tick-borne diseases,” Cabezas-Cruz points out.
Tick researchers are confident that their finding could lead to vaccinating wild animals in the future, which constitute a reservoir of pathogens, thus drastically reducing epidemics. Cabezas-Cruz points out that something similar is already being done, for example in Spain, with the population of wild boars, which are a reservoir of tuberculosis. These animals are fed food treated with the vaccine to stop them from spreading the disease. Now it can be the turn of ticks and blood-sucking species.
The warming has lengthened 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 covers more territories. Other factors may have influenced its proliferation, such as the presence of unharvested wood in the forests or the strategy of expanding green areas in urban centers.
The French Public Health (SPF) has revealed disturbing data on borreliosis. In 2009, 40 cases of the disease were detected for every 100,000 inhabitants. In 2020, it had gone 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 cause mild symptoms, similar to the flu, or digestive problems, but sometimes, if they are not treated in time or due to other circumstances, they evolve into serious conditions and can even cause death.
