Albergel, Jean

Diatta, Georges

Duplantier, Jean-Marc

Godeluck, Bruno

Legros, Fabrice

Pépin, Yannick

Rogier, C.

Trape, Jean-François

Horizon / Pleins textes

-p. 
Rocziki Akadeinii Medycznej w Biatymstoku 1996 vo1.41. Nr I, 136-141 
* TICK-BORNE BORRELIOSIS IN WEST AFRICA: RECENT 
EPIDEMIOLOGICAL STUDIES 
Jean-François TRAPE', Bruno GODELUCK', Georges DI ATTA', Christophe 
' ROGIER', Fabrice LEGROS', Jean ALBERCEL3, Yannick PEPIN', 
Jean-Marc DUPLANTIER4 ' 
I. Laboratoire de Paludologie, ORSTOM, B. P. 1386, Dakar, Sénégal 
2. Sewìce d'Epidétnìoiogie, Institut Pasteur, B. P. 220, Dakar, Sénégal 
3. Service d'Hydrologie, ORSTOM, B. P. 1386, Dakar, Sinégal 
4. Programme Eau & Santi, ORSTOM, B, P. 1386, D a h ,  Séndgal 
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ABSTRACT: Tick-borne borreliosis in West Africa is classically considered a rare 
disease whose geographic distribution is linlited to Saharan and Sahelian regions. 
We report results of epidenliological investigations which indicate that tick-borne 
borrehosis is endemic in  all regions of Senegal north to the 13'30" latitude and 
is a major cause of morbidity in these areas, Our findings indicate a considerable range 
extension for the vector tick Alectorobius sonrai and suggest that the ,persistence 
of Subsaharan drought is responsible for a large spread of tick-borne borreliosis i n  West 
Africa. 
Key words: Borrelia crociihìrue, Borreliosis, Relapsing fever, Alecforobius sonrui, 
Africa, Subsaharan drought. 
INTRODUCTION 
I n  West Africa, tick-borne borreliosis is due to the spirochaete ßorrclio 
.'*'crocidurue. Wild rodents and insectivores act as the reservoir for infcction and the only 
known vector is the ornithodorean tick Aleclorohifis sonrai. (1-4). This tick lives 
in  burrows and human contamination occurs classically when burrows open 
in bedrooms (4). After an incubation period of 4 days to two weeks, illness begills 
abruptly with high fever, shaking chills and headache. The first attack lasts about three 
days and is followed by an interval of about ten days without symptoms, after which 
an average of six relapses occur, each lasting about two days. Severe meningo- 
encephalitic complications can ensue (5). However, the prognosis is much better than 
with ß. dziffoni - which is endemic in East and Central Africa but absent from West 
Africa - and mortality rate is probably less than 0-5 per cent. 
Tick-borne borreliosis in West Africa is classically considered a rare disease 
and its geographic distribution is not well known (6) .  Most of the areas where the 
presence of the vector has been recorded are situated in Sahelian regions, from 
Mauritania and Northern Senegal to Tchad, where the average rainfall was less than SOO 
mm, and none reached the 750 mm isohyet which was considered the limit of vector's 
distribution (7). 
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BORRELIOSIS IN WEST AFRICA -- 
In order 
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MATERIALS AND METHODS 
to see how common relapsing fever is in Senegal thick blood smears 
RESULTS I .I *.., 
Epidemiological studies in Dielmo 
The mean study population was 235 people. A total of 24 cases of borreliosis 
were diagnosed during follow-up, an average annual incidence rate of 5.1%. Cases 
appeared sporadically throughout the duration of the study. Age of patients ranged from 
15 months to 52 years and no significant difference in the rate of incidence was 
observed in relation to age group. The daily recording of villager's presence and of their 
travelling was conclusive in precisely locating the place of infection for twenty patients 
, who had spent every night at home the month preceeding the start of clinical symptoms, 
137 
J.F. TRAPE 
A total of 25 1 rodents and insectivores were tested for B. crocidurue by direct 
examination of thick blood films and 232 were also studied by intraperitoneal 
inoculation of a white mouse. Two animals (0.8%) were found infected by the direct 
method (one M. erythroleucus and one A.  niIoticus) and seven animals (3.0%) by the 
inoculation method (G M. erytl7roleucus and one A.  niloficus). 8.2% o f  342 burrows 
examined during four surveys contained A. sonrai (8.5% inside houses and 7.1% in the 
fields). 
Batches of A. sonrai collected inside houses were ground in saline solution 
then inoculated intraperitonealy into white mice. Four of the batches developed 
to B. crocidurae infection in white mice. In six bedrooms of villagers who had recently 
suffered borreliosis, a sentinel white mouse was kept in a cage for one night. Two white 
mice developed an infection during the following days. 
, 
Distribution of A. sonrai in Senegal 
Between 14'30'N and 15"30'N, out of 278 burrow examined, 118 (42%) 
contained A. sonrai. The proportion of positive burraws in each of the three regions 
studied was 41%, 37% and 32%, respectively. Between 13'30" and 13'59'N, out 
of 465 burrows examined in five different regions (Dielmo village and one region per 
degree o f  longitude between 13"W and 17"W), 35 (75%) contained thc vector. At this 
latitude, we constantly found A. sotirui from the Atlantic Ocean on the West and to tlie 
Mali border on the East. Between 12O30'N and 13"29'N, we found A. sonrai in one 
single burrow (13"15'N, 13"12'W) out of 454 studied in six different regions (one 
region per degree of longitudc between I I OW and I7"W). 
Borreliosis in clinic outpatients 
In Keur Moussa, ß. crocidurue was found in smears from 12 (0.9%) of the 
1,340 children investigated. By age, the proportion of positive thick sinears was 0/490 
for children younger than 2 years old, 2/417 (0.5%) for those between 2 and 4, 5 1308 
( I  A%) for those between 5 and 9, and 511 19 (4.2%) for those between IO and 14. All 
patients who were positive complained of acute fever. 
I n  Mlomp, we tested 927 patients of all ages with acute fever, including 580 
children aged 5-14 years. No cases of infection were observed. 
Between 1989 and 1993, we documcntcd the origins of infection of 126 
patients fioin various medical units. With the possible exception o f  one single case 
(a patient who travelled in different localities of south-eastern Senegal), all of the 
patients were infected to the north of 13'30" latitude. 
I '  
B. crocidurae in small mammals 
Out of 2,164 rodents and insectivores belonging to 14 species captured in 23 
locations between 13"30'N and 16"30'N, 195 (9.0%) were found infected by direct 
thick blood filin examination (Table). Between 12'30" and 13'15'N, we tested for 
B. crocidurae 367 rodents captured in 13 different locations (9 in south eastern Senegal 
and 4 in Casamance). No cases of infection were observed. 
138 
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BORRELlOSlS IN WEST AFRICA 
Table I. List of species of small mammals found infected with Borrelia crocidurae 
in West Africa. 
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Relations to rainfall 
RODENTS 
Heliosciurus gambianus 
Desmodi I I iscus braueri 
Tatera gambiana 
Taterillus gracilis (complex) 
Cricetomys gambianus 
Arvicanth is ni lot icus 
Dasymys incomtus 
Mastomys erythroleucus 
Mastomys huberti 
Mastomys natalensis 
Mus musculus 
Myomis daltoni 
Rattus rattus 
Rattus norvegicus 
INSECTIVORES 
Crocidura sp. 
Atelerix albiventris 
data fiom the litterature 
Since the 7Sb mm isohyet has previously coincided with the known southerly 
limit of the vector, the drought in Subsaharan Africa, persistant since 1970, might 
explain the vector’s progression and the spread of the disease towards the south. 
In order to test this hypothesis, we mapped the average annual precipitations in Senegal 
for the periods 1947b.1969 and 1970-1992, and studied the relationship between the 
evolution of the rain gauge readings between these two periods of time and the present 
known distribution of the vector. 
Between 13”30’N and 13’59”’ the latitudes where we constantly found 
A .  sonrai for the first time, the average pluviometry have decreased by about 25% since 
the beginning of the clrought period. Whilst the average rainfall varied according to the 
regions from 850 mm to 1,000 mm for the period 1947-1969, it was always below 750 
, mm for the perkd 19’70-1992. Between 12O30’N and 13’30’N the average pluviometry 
decreased in similar ]proportions, but remained above 800 mm in each of the regions 
’ in which our studies were unable to demonstrate the presence of either A. sonrai 
or B. crocidurae. In trie case of the only area in which we found the vector, rain gauge 
readings of the station nearest to the collection locality of A. sonrai indicated an average 
of 749 mm for the period 1970- 1992. 
139 
J.F. TRAPE 
DISCUSSION 
Tick-borne borreliosis is endemic in all regions of Senegal north to the 13" 
30" latitude and is a major cause of morbidity in these areas. Investigations in Dielmo 
show for the first time that tick-borne borreliosis is locally transmitted in a Sudan 
savanna area of West Africa, with epidemiological features similar to those which liave 
been previously described in the Sahel (1-4, 7). 
Our findings indicate a considerable range extension for B. crocidirrae and its 
vector A, sonrai. The southern locality where the vector has been collected reaches 
13'15'N, i.e. more than one degree in latitude further south than its formerly known 
limit (7). 
We believe that the most probable explanation for our observations is that the 
spread of the endemic area has occurred recently and that the persistence of Subsaharan 
drought is responsible for a large spread of tick-borne borreliosis in West Africa 
by allowing the vector tick A ,  sonrai to colonize new savanna areas. This would be the 
first known example of a vector-borne disease whos'e spread in West Africa has been 
caused by present cliinatic changes. 
' 
BOI$ELIOZA W ZACHODNIEJ AFRYCE, AKTUALNE RADANIA 
E PIDE M IOLOG I CZN E 
S trcszczcii ic I 
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Borelioza z Lyme w Zachodnicj Afryce byla traktowana raczcj Jako rmdkn 
choroba, kt6rej geograficznc rozmicszczcnic jest ograniczonc do, rcgion6w Sallílry 
i Sahelu. Plzeprowadzono badania epidcmiologicznc, ktdru wsknziijq na cndcmicznc 
13030,, gdzie jest gt6wnym czynnikiem etiologicznym zachorowan. Wystçpowatnic 
wektora tcj choroby, kleszczy Alcctorobius sonrai i suszy w tyrn rcgionic 
wsp6ldecyduje o szerokim rozprzcstrzcnicniu sie tej choroby w Zachodnicj Af~ycc. 
I wystçpowanic boreliozy we wszystkich regionach Scnegalu na p6lnoc od r6wiiolctnika 
I 
REFERENCES 
I .  
2. 
Trape JF, Duplaiitier JM, Bouganali' Il, Codeluck B, Legros F, Cornct JI', 
Cainicas J L  (1991) Tick-borne borreliosis in West Africa. Lance1 337: 473-475. 
Codcluck B, Duplantier JM,  Ba K, Trape J F  (1994). A long¡ludinal survey 
of Borrelia crocidurae prevalence in rodents and insectivores in  Senegal. 
Ain J Trop Med Hyg SO: 165- I G8 
Rodhain F (1 976) Borrelia et fiévres récurrentes: aspects Cpiddmiologiques 
actuels. BUN Inst Pasteur 74: 173-2 I8  
Mathis C (1948) La spirochétose récurrente á tiques au Sénégal. I n :  L'oeuvre des 
Pastoriens en Afrique Noire (Afrique Occidentale Française). Paris: Presses 
Universitaire de France 
Connet C (1942) Complications méningées et oculaires de la fiévre récurrente 
africaine. Med Trop 2: 895-902 
. 
3. 
4. 
5. 
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BORRELlOSlS IN WEST AFRICA 
6. Trape JF, Godeluck B, Diatta G, Rogier C, Legros F, Albergel J, Pépin 
Y, Duplantier JM. The spread of tick-borne borreliosis in West Africa and its 
relation to Subsaharan drought. Am J Trop MeJ Hyg (inpress) 
Morel PC (1965) Les tiques d'Afrique et du Bassin méditerranéen. Maisons- 
Alfort: IEMVT 
Diatta C, Trape JF, Legros F, Rogier C, Duplantier JM (1994).A comparative 
study of three methods of detection of Borrelia crocidurae in wild rodents 
in Senegal. Trans Roy Soc Trop Med Hyg 88: 423-424. 
Matheron C (1965) Les variables rCgionalisCes et leur estimation. Paris: Masson 
7. 
8. 
9. 
Author's address: Dr Jean Francois Trape, Orstom B. P. 1386 Dakar, Senegal 
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Tick-borne borreliosis in West Africa : recent epidemiological studies

Tick-borne borreliosis in West Africa : recent epidemiological studies

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