The human vector of Borrelia crocidurae in West Africa is the tick Ornithodoros sonrai, which lives in burrows of small wild rodents and is therefore in close contact with them. This disease was considered rare up to the end of the 1980s when a team of IRD researchers showed that in a rural area of the Dakar region tick-borne relapsing fever was the second most frequent reason for patients’ consultation at the local dispensary.
Since 1990, the IRD launched a comprehensive research programme on this disease, first in Senegal, then in the whole of West Africa. In Senegal, the investigation showed that the tick had colonized savannah and that the disease’s expansion was closely linked with the decrease in average rainfall since the long drought began in 1970. The advance of borreliosis prompted the research team to extend their epidemiological research and study the long-term trends, by 14 years of measurement of the infection’s incidence in a rural Senegalese community which was the subject of continuous demographic and health monitoring programme run jointly by the IRD, the Pasteur Institute and the University of Dakar.
The study was conducted from 1990 to 2003 on people in Dielmo, a village in the savannah in the Sine-Saloum region of Senegal, in order to determine the frequency and describe the clinical manifestations of malaria, tick-borne relapsing fever and other fevers not linked to these two diseases. The research team lived permanently in the village so that they could visit each inhabitant daily. Medical examinations and biological tests were systematically carried where someone had a fever or other symptoms that might signal the disease. The presence of Borrelia crocidurae was also tested in people without symptoms at least once a year. All rodent burrows near houses and inner yards of concession were counted and recorded. They were searched for ticks and the latter’s infection rate by the bacterium determined. Rodents and insectivores were captured in order to study the bacterial reservoir.
Over the period of study as a whole, an average 11 % of the population suffered from borreliosis each year, an exceptional incidence rate for a disease, whatever its cause. Only malaria, among the parasitic diseases and in any case to a lesser degree, and influenza, among viral diseases, are known to produce a comparable incidence level over such a long period. Tick-borne relapsing fever is the second cause of illness after malaria. All age groups were affected by it in the population studied.
The IRD team then conducted systematic surveys in Senegal, Mali and Mauritania in order to define the geographical distribution of the tick, determine the infection rate over the whole of its area of distribution and establish the proportion of villages affected by the disease. The results showed that the vector is present in massive numbers in these three countries in any area where average rainfall is below 750 mm. Out of 30 villages studied, 26 (87 %) were colonized by the tick which was present on average in 31 % of the burrows in the villages with a Borrelia crocidurae infection rate of 21 %. Two-thirds of the villages studied showed an exposure rate to tick-borne relapsing fever among inhabitants even higher than that of the people in Dielmo. It is in most of the rural areas of Senegal and Mali and in all parts of Mauritania that the disease is a major public health problem.
Paradoxically, this emerging disease is still completely misunderstood by health care personnel, although it has become one of the most frequent bacterial infections. Laboratory testing for determining the cause of a disease is rarely possible in tropical Africa, particularly in the rural areas. Borrelia crocidurae can be detected in blood samples only during peaks of fever. Its density is usually very low and diagnosis requires the skills of an experienced microscopist. The symptoms of the disease are exactly similar to those of malaria which is very frequent in the same populations. The disease is therefore systematically confused with malaria, and failure of treatment is attributed to antimalarial drugs. Furthermore, the existence of an animal reservoir and the omnipresence of rodents in rural areas makes prevention of the disease hardly feasible. However, a cheap effective treatment is possible which involves the use of antibiotics of the tetracycline family which are available in most clinics in the bush.
Marie Guillaume | alfa
Protein 'spy' gains new abilities
28.04.2017 | Rice University
How Plants Form Their Sugar Transport Routes
28.04.2017 | Universität Heidelberg
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Life Sciences
28.04.2017 | Life Sciences
28.04.2017 | Life Sciences