Some 50 European, African and Latin American institutions are participating, with Union support, in the third ICCTD (International Consortium on Ticks and Tick-borne Diseases) initiative. For the past eight years, this network has harnessed the efforts of more than 150 researchers who have resolved to combat, by different and complementary means, the damage caused by these particularly vigorous arachnids which wreak such havoc on livestock herds.
Minute parasites when they settle on the skin of mammals, ticks subsequently swell up as they absorb their victim's blood and can be the carriers of sometimes fatal diseases. Particularly vigorous and prolific, they exist in many forms and at every latitude. Anyone who takes a walk in the countryside, especially with a dog as companion, must surely be aware of them. But the damage caused in northern countries – even if they can have serious consequences for humans, in particular as the source of infection with Lyme disease – bears no comparison to the disasters they can cause in developing countries where they can decimate livestock herds.
|Attack by Rhipicephalus appendiculatus (Zambia). In the southern hemisphere alone, around 870 species of tick are potential carriers of disease, and many different varieties can be found in the same region.|
The first problem these ‘bloodsuckers' cause cattle, sheep and other small ruminants is anaemia, resulting in weight loss and thus loss of earnings for the rearers. Their skin is also damaged by the bites and loses its value. In addition to this ‘direct' damage, these parasites also transmit diseases such as anaplasmosis, cowdriosis, dermatopholosis, theilerois and babesiosis that cause losses among livestock in tropical and subtropical countries that are estimated to cost billions of euros a year.
Variety of weapons
"The problem is all the more crucial as, in the southern hemisphere, about 870 species of tick have been identified as having the potential to transmit disease. What is more, a large number of these species can be present in the same region. This means that even when a response is found for one type of parasite, such as a vaccine against a disease carried by one species, additional methods, such as acaricides, must continue to be used to combat the other types of tick. That is why we are seeking polyvalent methods,” explains Frans Jongejan of Utrecht University's Faculty of Veterinary Medicine (NL), coordinator of the action since it was launched in 1996.
The ITCCD already received Union support under the Fourth Framework Programme and has just received its ‘third mandate' under the Sixth Framework Programme with financial aid of €1 842 000 over a 48-month period. From the outset, this long-term effort has concentrated on a triple strategy.
|On the left, Amblyomma variegatum (female tick) and on the right, Rhipicephalus humeralis – (male tick).|
First of all, on the prevention front researchers are working on new multi-component vaccines that target both the parasites themselves and the diseases they transmit. This aspect is all the more important as the ticks have a tendency to develop a growing resistance to the chemical substances designed to destroy them. The massive use of these acaricides also poses serious problems from an environmental point of view.
Other network laboratories are concentrating on perfecting screening tests, in particular diagnostic tests that can be applied simultaneously to different pathogenic agents. Finally, epidemiological studies are being carried out to assess the socio-economic impact of tick-borne diseases.
Over the coming years, the ICTTD will organise its activities into working groups. The Database working group is compiling a huge database (THP base) of available information on three elements: the ticks, their victims (H for ‘host') and the pathogenic agents. This knowledge should make it possible to arrive at an improved diagnosis of the various diseases by comparing medical data with ecological or climatic data so as to be able to define the geographical distribution of tick species and of diseases in subtropical regions. The four avenues of research – Biosystematics Forum, Molecular Diagnostic Network, Genomic and Vaccine Design Group and Study Group on Tick-Host-Pathogen Interactions – are aimed primarily at improving biological knowledge of a nature to bring further progress in combating this plague. It is particularly important to understand the interaction between the ticks, their hosts and the diseases caused as well as to establish the genomic and proteomic data that could be used in launching new vaccines.