7 f 0 INSTITUT PASTEUR/ELSEVIER I Res....
7
f
0 INSTITUT PASTEUR/ELSEVIER
I
Res. Virol.
Paris 1991
I -, .c- 1;
-4
‘
1991, 142, 67-70
/
‘. ‘.-” C:‘,
:” ’
‘:
i;* /I . I
L-L!&
!
- / :. _ /
BRIEF NOTE
Changes in Rift Valley fever neutralizing antibody prevalence
among small domestic ruminants following the 1987
outbreak in the Senegal River basin
Y. Thiongane (l), J.P. Gonzalez (2), A. Fati (3) and J.A. Akakpo (3)
(1) Institut Sénégalais de Recherches agricoles (ISRA), BP 2057, Dakar-Hum (Sénégal)
(2) Institut Français de Recherche Scientifique pour le Développement en Coopération
(ORSTOM), Dakar, and
(3) Ecole Inter-Etats de Science et Médecine Vétérinaires (EISMV), BP 5077, Dakar
SUMMARY
Following the Rift Valley fever (RVF) epizootic of 1987 in the Senegal River basin,
2 series of serosurveys were carried out. In 1988 and 1989, respectively, 303 and 331
randomly selected sheep and goats were investigated and sera tested for the presence
of specific RVF-virus-neutralizing antibodies.
In 1988,24.4 % of the sera was found to have anti-RVF neutralizing antibodies and
in 1989, 19.3 % was found. In 1988, we observed in the Dagana district, including
the 1987 epizootic area, a signiffcantly higher prevalence (7 1.1 %) than in the two other
more distant districts of Podor (21.5 %I and Matam (9.7 %). From 1988 to 1989, the
antibody seroprevalence dropped significantly from 71.7 to 23.9 % within the Dagana
district. Young animals showed a significantly lower antibody prevalence (7.9 %,
N = 114) than adults (25.3 %, N = 2171.
RVF virus circulated at a low level in 1988-89 without any epizootic manifestation.
The population turnover generated an important non-immune population potentially at
risk.
Key-words: Senegal, RVF, Neutralizing antibody; Serosurvey, Senegal River basin,
Sheep, Goats.
INTRODUCTION
Epizooties are precursor manifestations of epi-
Rift Valley fever (RVF) is an African ar-
demies (Ksiazeck et al., 1989; Lancelot et a/.,
boviral zoonosis that is transmitted by mosqui-
1989). Enzootic maintenance of the virus is de-
toes.
Severe epizootic and epidemic
pendent on physical factors related to the rela-
manifestations have occurred during the past two
tive abundance of potential vectors and hosts
decades in Africa (Peters and Meegan, 1988).
(Davies et al., 1985 ; Peters and Meegan, 1988).
Submitted December 21, 1990, accepted January 2, 1991.
-
68
Y. THIONGANE ET AL.
Despite the degree of knowledge of such risk fac-
RESULTS AND DISCUSSION
tors within a specific area, an intensive serosur-
vey of domestic ruminants remains the most
In 1988, there was a highly significant differ-
convenient way to detect any RVF virus activi-
ence between the RVF antibody prevalence in
ty even at a low level. Moreover, there is a need
the Dagana district (71.7 vo) and the two others,
for a longitudinal study in order to understand
Podor (21.5 070) and Matam (9.7 Yo) (p < 0.001
the real impact of the virus on livestock in trop-
by Chi-square test). Consequently, a negative gra-
ical Africa.
dient of RVF virus antibody prevalence from the
delta to the Upper Senegal River basin was ob-
Recent epidemic and epizootic manifestations
served. The Dagana district, which is closely
in the southern Mauritania (Jouan et al., 1989)
related to southern Mauritania where a major
prompted us to start a serosurvey of RVF in
epidemic was recorded in 1987, showed the
domestic ungulates from the Senegal River ba-
highest positive rate. Moreover, the highest an-
sin and to annually assess the risk for the non-
tibody prevalence in small ruminants was found
immune populations.
by Kiazeck et al. (1989) in the same Dagana area
on both sides of the river, compared to the
coastal area and middle and Upper river basin
MATERIALS AND METHODS
where RVF antibody prevalence remained signifi-
cantly lower. In 1989, a significant difference no
Study area
longer existed (p > 0.05). From 1988 to 1989,
The delta, lower and middle Senegal River Basin
the RVF antibody prevalence dropped globally
(fig. 1) including the 1987 area of major epidemic and
epizootic manifestation, were targeted to identify any
change in the rate of specific RVF virus antibody
prevalence. The localities under study are a11 includ-
MAURITANIA
ed in the Sahelian edaphic zone of West Africa with
17
an annual rainfall of less than 600 mm, and are
described in detail elsewhere (Jouan et al., 1989;
Guillaud et al., 1989).
16
Sampling method
Sheep and goats randomly selected were bled in
August 1988 and 1989, at the beginning of the rainy
....
....
season, which lasts for 3 to 4 months. Blood sam-
100h
~
......
. .
...... .....
ples were drawn by jugular venipuncture, sera decant-
ed following clot formation and stored at -20°C
prior to laboratory testing.
Fig. 1. Map of locality where animal populations are sur-
veyed for RVF in the Senegal River basin.
Darkened area on the map represents the major enzoot-
Neutralizing test
ic and epizootic region recorded during the 1987 RVF out-
break. Dashed lines stand for district limits.
Neutralizing antibody test was performed using
Study localities : 1 = Raïnadé, 2 = Rosso, 3 = Colonat,
Vero monolayer cells infected with a viral suspension
4 = Niassante,
5 = Thille
Boubacar,
6 = Podor,
7 = NDioum,
8 = Dere
Lao,
9 = Goudoude,
of titre 106.5 PFU/ml at a dilution of 1/1,600 RVF
10 = Ourossogui, 11 = Kanel.
virus Smithburn strain. In accordance with a previ-
1 = Dagana district including the delta and lower Sene-
ously described method, antibody-positive sera were
gal River basin. II and III = Podor and Matam districts in-
determined by the lack of cytopathogenic effect at
cluding the middle Senegal River basin and part of the
the serum dilution of 1/160 (Davies et al., 1988).
Upper Senegal River basin upstream from Matam.
RVF
= Rift Valley fever.
ELISA = enzyme-linked immunosorbent assay.
R VF ANTIBODY SEROSUR VEYS OF SENEGALESE ANIMALS
69
from 24.4 % to 19.3 % (table 1). For the
and herders favouring intensive animal repro-
Dagana district, only the loss of neutralizing an-
duction to recover the dramatic loss by abortion
tibody was significant, from 71.7 to 23.9 %
from the 1987 epizotic (Lancelot et al., 1989),
(p < 0.001).
thereby increasing the non-immune population.
A more detailed analysis done on the 1989 se-
On one hand, low level RVF virus activity was
rum samples (table II) showed no significant
observed on detecting IgM seropositive sheep
difference in antibody prevalence (p > 0.05) be-
during the interepizootic period in the Senegal
tween sheep and goats, as previously observed
River basin (Saluzzo et al., 1987; Gonzalez et
in this area by Guillaud et al. (1988) using an
al., 1989), and on the other hand, in the present
ELISA test. However, Young animals had a sig-
paper, a dramatic increase in the non-immune
nificantly lower antibody prevalence (7.9 070,
population during these two past years is shown.
N=114, x=9) than adults (25.3 %, N=217,
Conclusively, the declining antibody protection
x = 55) (p < 0.001). This last observation cari be
in the flocks and the presence of RVF virus in
explained by a change in the structure of the
the Senegal River basin, increases the risk of an
population, with older animals being slaughtered
epizootic, and hence an epidemic, in the com-
first, thus decreasing the immune population,
ing rainy seasons in relation to vector activity.
Modifications de la prévalence des anticorps
Table 1. Prevalence of RVF-virus-neutralizing
neutralisan ts an ti-virus de la fièvre
antibodies in small ruminants from the Senegal River
de la Vallée du Rift chez les petits ruminants
basin in 1988.
domestiques à la suite de l’épidémie de 1987
dans le bassin versant du fleuve Sénégal
Date of sampling
Department
of origin
1988
1989
Deux séries d’enquêtes sérologiques ont été
menées dans la région du bassin versant du fleuve
Dagana
28/39 (71.7)
38/159 (23.9)
Sénégal où a eu lieu une manifestation épidémoépi-
Podor
37/172 (21.5)
181115 (15.7)
zootique du virus de la fièvre de la Vallée du Rift
Matam
9/92 (9.7)
8/57 (14.0)
(FVR) en 1987. Deux échantillons de sérums ont été
prélevés respectivement en 1988 et en 1989 chez 303
Total
74/303 (24.4)
641331 (19.3)
et 331 petits ruminants (chèvres et moutons) pris au
hasard et ont été testés pour la mise en évidence
Results shown = positivekota tested (Vo).
d’anticorps neutralisants. Sur les 634 animaux tes-
tés au total et respectivement en 1988 et en 1989, la
séroprévalence est de 24,4 et 19,3 %.
Table II. Comparative seroprevalence on small
En 1988, dans le département de Dagana parti-
ruminants by species, age and origin in the Senegal
culièrement touché par l’épizootie de 1987, la pré-
River basin in 1989.
valence en anticorps est significativement plus élevée
(71,7 070) par rapport aux départements de Podor
District Age
Sheep
Goat
(21,5 070) et de Matam (9,7 olo) situés plus en amont
sur le cours du fleuve.
Dagana Adult
14/43 (32.6)
22/58 (37.9)
De 1988 à 1989, on observe une chute de la pré-
Juvenile
2/39 (5.1)
0/19 (0.0)
valence des anticorps neutralisants de 71,7 à 23,9 %
Podor
Adult
8/56 (14.3)
3/17 (17.6)
dans le département de Dagana.
Juvenile
6/33 (18.2)
1/9 (11.1)
La prévalence en anticorps neutralisant contre
Matam Adult
6/24 (25 .O)
2/19 (10.5)
l’antigène RVF est significativement moins élevée
Juvenile
O/ll (0.0)
0/3 (0.0)
chez les jeunes animaux (7,9 Oro) que chez les adultes
Total
Adult
28/123 (22.7) 27/94 (28.7)
(25,3 VO).
Juvenile
8/83 (9.6)
1/31 (3.2)
Dans la période post-épizootique de 1988 à 1989,
Both
36/206 (17.4) 28/125 (22.4)
une surveillance suivie permet de conclure en faveur
d’une absence de circulation active du virus de la FVR
Results shown = positive/total tested (Vo).
chez les ruminants domestiques du Nord-Sénégal.
70
Y. THIONGANE ET AL.
”
Le renouvellement rapide de la population.non
tical study of a Rift Valley fever epidemic. Res. Col.,
immune de petits ruminants représente un risque
140, 175-186.
potentiel épizootique et secondairement épidémique
Ksiazek, T., Jouan, A., Meegan, J.M., Le Guenno, B.,
dans cette zone sahélienne d’enzootie connue.
Wilson, M., Peters, C.J., Digoutte, J.P., Guillaud,
M., Ould Merzoug, N. & Touray, E.M. (1989), Rift
Valley fever among domestic animais in the recent
Mots-clés: Sénégal, FVR, Anticorps neutralisant ;
West African outbreak. Rex Virol., 140, 67-77.
Bassin versant du fleuve, Petits ruminants domesti-
Gonzalez, J.P., Wilson, M.L., Diop, A., Fortez, C. &
ques, Epidémiologie.
Adam, F. (1989), Laboratoire de Virologie Expéri-
mentale ; le virus Ngari, in “Rapport sur le fonction-
nement technique de l’Institut Pasteur”
(J.P. Digoutte) (pp. 129-131). Institut Pasteur de
Dakar, Dakar.
Guillaud, M., Le Guenno, B., Wilson, M.L., Desoutter,
D., Gonzalez, J.P. & Digoutte, J.P. (1988), Préva-
References
lente en anticorps contre le virus de la fièvre de la val-
lée du Rift chez les petits ruminants du Sénégal. Ann.
Davies, F.G., Jacobsen, P. & Sylla, D. (1988), Laboratory
ht. PasteurWirol., 139, 455-459.
manual on Rift Valley fever : isolation and identifi-
Lancelot, R., Gonzalez, J.P., Le Guenno, B., Diallo, B.C.,
cation technics, in “Report of FAO/WHO group on
Gandega, Y. & Guillaud, M. (1989), Epidémiologie
emergency preparedness for Rift Valley fever control
descriptive de la fièvre de la vallée du Rift chez les
in West Africa” (pp. 1-134). WHO-VPH/88.77.
petits ruminants dans le Sud de la Mauritanie après
Davies, F.G., Linthicum, K.J. & James, A.D. (198.5), Rain-
l’hivernage 1988. Rev. Elev. Méd. vét. Pays trop., 42,
fa11 and epizootic Rift Valley fever. Bull. Org. mond.
485-49 1.
Santé, 63, 941-943.
Peters, C.J. & Meegan, J.M. (1987), Rift Valley fever, in
Jouan, A., Coulibaly, I., Adam, F., Philippe, B.,
“CRC hand-book series in zoonoses” (vol. 1)
Riou, O., Le Guenno, B., Christie, R., Ould Mer-
(G.W. Beran & J.H. Steele) (pp. 403-420). CRC
Zoug, N., Ksiazek, T. & Digoutte, J.P. (1989), Analy-
Press, Boca Raton, FL.
f
0 INSTITUT PASTEUR/ELSEVIER
I
Res. Virol.
Paris 1991
I -, .c- 1;
-4
‘
1991, 142, 67-70
/
‘. ‘.-” C:‘,
:” ’
‘:
i;* /I . I
L-L!&
!
- / :. _ /
BRIEF NOTE
Changes in Rift Valley fever neutralizing antibody prevalence
among small domestic ruminants following the 1987
outbreak in the Senegal River basin
Y. Thiongane (l), J.P. Gonzalez (2), A. Fati (3) and J.A. Akakpo (3)
(1) Institut Sénégalais de Recherches agricoles (ISRA), BP 2057, Dakar-Hum (Sénégal)
(2) Institut Français de Recherche Scientifique pour le Développement en Coopération
(ORSTOM), Dakar, and
(3) Ecole Inter-Etats de Science et Médecine Vétérinaires (EISMV), BP 5077, Dakar
SUMMARY
Following the Rift Valley fever (RVF) epizootic of 1987 in the Senegal River basin,
2 series of serosurveys were carried out. In 1988 and 1989, respectively, 303 and 331
randomly selected sheep and goats were investigated and sera tested for the presence
of specific RVF-virus-neutralizing antibodies.
In 1988,24.4 % of the sera was found to have anti-RVF neutralizing antibodies and
in 1989, 19.3 % was found. In 1988, we observed in the Dagana district, including
the 1987 epizootic area, a signiffcantly higher prevalence (7 1.1 %) than in the two other
more distant districts of Podor (21.5 %I and Matam (9.7 %). From 1988 to 1989, the
antibody seroprevalence dropped significantly from 71.7 to 23.9 % within the Dagana
district. Young animals showed a significantly lower antibody prevalence (7.9 %,
N = 114) than adults (25.3 %, N = 2171.
RVF virus circulated at a low level in 1988-89 without any epizootic manifestation.
The population turnover generated an important non-immune population potentially at
risk.
Key-words: Senegal, RVF, Neutralizing antibody; Serosurvey, Senegal River basin,
Sheep, Goats.
INTRODUCTION
Epizooties are precursor manifestations of epi-
Rift Valley fever (RVF) is an African ar-
demies (Ksiazeck et al., 1989; Lancelot et a/.,
boviral zoonosis that is transmitted by mosqui-
1989). Enzootic maintenance of the virus is de-
toes.
Severe epizootic and epidemic
pendent on physical factors related to the rela-
manifestations have occurred during the past two
tive abundance of potential vectors and hosts
decades in Africa (Peters and Meegan, 1988).
(Davies et al., 1985 ; Peters and Meegan, 1988).
Submitted December 21, 1990, accepted January 2, 1991.
-
68
Y. THIONGANE ET AL.
Despite the degree of knowledge of such risk fac-
RESULTS AND DISCUSSION
tors within a specific area, an intensive serosur-
vey of domestic ruminants remains the most
In 1988, there was a highly significant differ-
convenient way to detect any RVF virus activi-
ence between the RVF antibody prevalence in
ty even at a low level. Moreover, there is a need
the Dagana district (71.7 vo) and the two others,
for a longitudinal study in order to understand
Podor (21.5 070) and Matam (9.7 Yo) (p < 0.001
the real impact of the virus on livestock in trop-
by Chi-square test). Consequently, a negative gra-
ical Africa.
dient of RVF virus antibody prevalence from the
delta to the Upper Senegal River basin was ob-
Recent epidemic and epizootic manifestations
served. The Dagana district, which is closely
in the southern Mauritania (Jouan et al., 1989)
related to southern Mauritania where a major
prompted us to start a serosurvey of RVF in
epidemic was recorded in 1987, showed the
domestic ungulates from the Senegal River ba-
highest positive rate. Moreover, the highest an-
sin and to annually assess the risk for the non-
tibody prevalence in small ruminants was found
immune populations.
by Kiazeck et al. (1989) in the same Dagana area
on both sides of the river, compared to the
coastal area and middle and Upper river basin
MATERIALS AND METHODS
where RVF antibody prevalence remained signifi-
cantly lower. In 1989, a significant difference no
Study area
longer existed (p > 0.05). From 1988 to 1989,
The delta, lower and middle Senegal River Basin
the RVF antibody prevalence dropped globally
(fig. 1) including the 1987 area of major epidemic and
epizootic manifestation, were targeted to identify any
change in the rate of specific RVF virus antibody
prevalence. The localities under study are a11 includ-
MAURITANIA
ed in the Sahelian edaphic zone of West Africa with
17
an annual rainfall of less than 600 mm, and are
described in detail elsewhere (Jouan et al., 1989;
Guillaud et al., 1989).
16
Sampling method
Sheep and goats randomly selected were bled in
August 1988 and 1989, at the beginning of the rainy
....
....
season, which lasts for 3 to 4 months. Blood sam-
100h
~
......
. .
...... .....
ples were drawn by jugular venipuncture, sera decant-
ed following clot formation and stored at -20°C
prior to laboratory testing.
Fig. 1. Map of locality where animal populations are sur-
veyed for RVF in the Senegal River basin.
Darkened area on the map represents the major enzoot-
Neutralizing test
ic and epizootic region recorded during the 1987 RVF out-
break. Dashed lines stand for district limits.
Neutralizing antibody test was performed using
Study localities : 1 = Raïnadé, 2 = Rosso, 3 = Colonat,
Vero monolayer cells infected with a viral suspension
4 = Niassante,
5 = Thille
Boubacar,
6 = Podor,
7 = NDioum,
8 = Dere
Lao,
9 = Goudoude,
of titre 106.5 PFU/ml at a dilution of 1/1,600 RVF
10 = Ourossogui, 11 = Kanel.
virus Smithburn strain. In accordance with a previ-
1 = Dagana district including the delta and lower Sene-
ously described method, antibody-positive sera were
gal River basin. II and III = Podor and Matam districts in-
determined by the lack of cytopathogenic effect at
cluding the middle Senegal River basin and part of the
the serum dilution of 1/160 (Davies et al., 1988).
Upper Senegal River basin upstream from Matam.
RVF
= Rift Valley fever.
ELISA = enzyme-linked immunosorbent assay.
R VF ANTIBODY SEROSUR VEYS OF SENEGALESE ANIMALS
69
from 24.4 % to 19.3 % (table 1). For the
and herders favouring intensive animal repro-
Dagana district, only the loss of neutralizing an-
duction to recover the dramatic loss by abortion
tibody was significant, from 71.7 to 23.9 %
from the 1987 epizotic (Lancelot et al., 1989),
(p < 0.001).
thereby increasing the non-immune population.
A more detailed analysis done on the 1989 se-
On one hand, low level RVF virus activity was
rum samples (table II) showed no significant
observed on detecting IgM seropositive sheep
difference in antibody prevalence (p > 0.05) be-
during the interepizootic period in the Senegal
tween sheep and goats, as previously observed
River basin (Saluzzo et al., 1987; Gonzalez et
in this area by Guillaud et al. (1988) using an
al., 1989), and on the other hand, in the present
ELISA test. However, Young animals had a sig-
paper, a dramatic increase in the non-immune
nificantly lower antibody prevalence (7.9 070,
population during these two past years is shown.
N=114, x=9) than adults (25.3 %, N=217,
Conclusively, the declining antibody protection
x = 55) (p < 0.001). This last observation cari be
in the flocks and the presence of RVF virus in
explained by a change in the structure of the
the Senegal River basin, increases the risk of an
population, with older animals being slaughtered
epizootic, and hence an epidemic, in the com-
first, thus decreasing the immune population,
ing rainy seasons in relation to vector activity.
Modifications de la prévalence des anticorps
Table 1. Prevalence of RVF-virus-neutralizing
neutralisan ts an ti-virus de la fièvre
antibodies in small ruminants from the Senegal River
de la Vallée du Rift chez les petits ruminants
basin in 1988.
domestiques à la suite de l’épidémie de 1987
dans le bassin versant du fleuve Sénégal
Date of sampling
Department
of origin
1988
1989
Deux séries d’enquêtes sérologiques ont été
menées dans la région du bassin versant du fleuve
Dagana
28/39 (71.7)
38/159 (23.9)
Sénégal où a eu lieu une manifestation épidémoépi-
Podor
37/172 (21.5)
181115 (15.7)
zootique du virus de la fièvre de la Vallée du Rift
Matam
9/92 (9.7)
8/57 (14.0)
(FVR) en 1987. Deux échantillons de sérums ont été
prélevés respectivement en 1988 et en 1989 chez 303
Total
74/303 (24.4)
641331 (19.3)
et 331 petits ruminants (chèvres et moutons) pris au
hasard et ont été testés pour la mise en évidence
Results shown = positivekota tested (Vo).
d’anticorps neutralisants. Sur les 634 animaux tes-
tés au total et respectivement en 1988 et en 1989, la
séroprévalence est de 24,4 et 19,3 %.
Table II. Comparative seroprevalence on small
En 1988, dans le département de Dagana parti-
ruminants by species, age and origin in the Senegal
culièrement touché par l’épizootie de 1987, la pré-
River basin in 1989.
valence en anticorps est significativement plus élevée
(71,7 070) par rapport aux départements de Podor
District Age
Sheep
Goat
(21,5 070) et de Matam (9,7 olo) situés plus en amont
sur le cours du fleuve.
Dagana Adult
14/43 (32.6)
22/58 (37.9)
De 1988 à 1989, on observe une chute de la pré-
Juvenile
2/39 (5.1)
0/19 (0.0)
valence des anticorps neutralisants de 71,7 à 23,9 %
Podor
Adult
8/56 (14.3)
3/17 (17.6)
dans le département de Dagana.
Juvenile
6/33 (18.2)
1/9 (11.1)
La prévalence en anticorps neutralisant contre
Matam Adult
6/24 (25 .O)
2/19 (10.5)
l’antigène RVF est significativement moins élevée
Juvenile
O/ll (0.0)
0/3 (0.0)
chez les jeunes animaux (7,9 Oro) que chez les adultes
Total
Adult
28/123 (22.7) 27/94 (28.7)
(25,3 VO).
Juvenile
8/83 (9.6)
1/31 (3.2)
Dans la période post-épizootique de 1988 à 1989,
Both
36/206 (17.4) 28/125 (22.4)
une surveillance suivie permet de conclure en faveur
d’une absence de circulation active du virus de la FVR
Results shown = positive/total tested (Vo).
chez les ruminants domestiques du Nord-Sénégal.
70
Y. THIONGANE ET AL.
”
Le renouvellement rapide de la population.non
tical study of a Rift Valley fever epidemic. Res. Col.,
immune de petits ruminants représente un risque
140, 175-186.
potentiel épizootique et secondairement épidémique
Ksiazek, T., Jouan, A., Meegan, J.M., Le Guenno, B.,
dans cette zone sahélienne d’enzootie connue.
Wilson, M., Peters, C.J., Digoutte, J.P., Guillaud,
M., Ould Merzoug, N. & Touray, E.M. (1989), Rift
Valley fever among domestic animais in the recent
Mots-clés: Sénégal, FVR, Anticorps neutralisant ;
West African outbreak. Rex Virol., 140, 67-77.
Bassin versant du fleuve, Petits ruminants domesti-
Gonzalez, J.P., Wilson, M.L., Diop, A., Fortez, C. &
ques, Epidémiologie.
Adam, F. (1989), Laboratoire de Virologie Expéri-
mentale ; le virus Ngari, in “Rapport sur le fonction-
nement technique de l’Institut Pasteur”
(J.P. Digoutte) (pp. 129-131). Institut Pasteur de
Dakar, Dakar.
Guillaud, M., Le Guenno, B., Wilson, M.L., Desoutter,
D., Gonzalez, J.P. & Digoutte, J.P. (1988), Préva-
References
lente en anticorps contre le virus de la fièvre de la val-
lée du Rift chez les petits ruminants du Sénégal. Ann.
Davies, F.G., Jacobsen, P. & Sylla, D. (1988), Laboratory
ht. PasteurWirol., 139, 455-459.
manual on Rift Valley fever : isolation and identifi-
Lancelot, R., Gonzalez, J.P., Le Guenno, B., Diallo, B.C.,
cation technics, in “Report of FAO/WHO group on
Gandega, Y. & Guillaud, M. (1989), Epidémiologie
emergency preparedness for Rift Valley fever control
descriptive de la fièvre de la vallée du Rift chez les
in West Africa” (pp. 1-134). WHO-VPH/88.77.
petits ruminants dans le Sud de la Mauritanie après
Davies, F.G., Linthicum, K.J. & James, A.D. (198.5), Rain-
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