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
When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short
23.03.2017 | Institut für Pflanzenbiochemie
WPI team grows heart tissue on spinach leaves
23.03.2017 | Worcester Polytechnic Institute
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
23.03.2017 | Life Sciences
23.03.2017 | Power and Electrical Engineering
23.03.2017 | Earth Sciences