Barbazan, Philippe

Cartel, J.L.

Martin, P.M.V.

Nguyen, L.

Roux, J.F.

Spiegel, A.

Séchan, Yves

Horizon / Pleins textes

Cumulative mortality rates in Aedes polynesiensis after feeding 
on Polynesian Wuchereria bancrofti carriers treated with single 
doses of ivermectin, diethylcarbamazine and placebo 
J.-L. Cartel, Y. Sechan, A. Spiegel, L. Nguyeit, Ph. Barbazaiz, P. M. V. Martin, J.-F. Roux 
Institut Territorial de Recherches Medicales Louis Malarde, Papeete, Tahiti, Polynesie Francaise 
Abstract 
During a therapeutic trial, batches of 672 to 
1979 laboratory-bred Aedespolynesietzsis, the mosquito vec- 
tor of lymphatic filariasis in French Polynesia, were fed on 
Wuchereria baiicrofti carriers one, three and six months 
after they had been treated with either single doses of iver- 
mectin a t  100 mcg/kg, diethylcarbamazine (DEC) at 3 and 
6 mg/kg or placebo. High mortality, rates were observed 
during the 15-day period following the blood-meal in 
mosquitoes fed on carriers treated with microfilaricidal 
drugs and were significantly higher in mosquitoes fed on 
carriers treated with ivermectin than in those fed on carriers 
treated with DEC. Though its intensity decreased with the 
passage of time, the phenomenon was observed in mosqui- 
toes fed on carriers up to six months after treatment, espe- 
cially in those fed on carriers treated with ivermectin. By 
decreasing the number of mosquitoes able to transmit the 
infection, this lethal effect on Ae. polynesiensis might repre- 
sent an additional advantage of ivermectin in lymphatic 
filariasis control programmes. 
Introduction 
The results of a single-blind, dose-ranging 
study conducted in French Polynesia between 1986 and 1988 
have indicated that a single dose of 100 mcg/kg ivermectin re- 
sulted in the best efficacy and treatment tolerance for Wuclzere- 
riu bancrofti carriers (Roux et al., 1989). Also, a single 200 
mcg/kg dose induced a reduction in transmission by the vec- 
tor Aedes polynesiensis (Cartel et al., 1990). Therefore, in 
1989, a double-blind, placebo-controlled trial was imple- 
mented, the objectives of which were (i) to compare the effi- 
cacy and safety of single doses of ivermectin at 100 mcg/kg, di- 
ethylcarbamazine (DEC) at 3 mg/kg (the current standard 
regimen for mass treatment of Bancroftian filariasis in French 
Polynesia) and DEC at 6 mg/kg and (ii) to determine the ef- 
fects of these 3 regimens on transmission by mosquitoes fed on 
carriers treated with effective drugs as compared to those fed 
on placebo treated carriers. 
Accepted 30 August 1991 
Trop.Med. Parasito1.42(1991)343-345 
O GeorgThieme Verlag Stuttgart.NewYork 
Materials and methods 
Of 68 microfilariae (mo carriers who were included 
in the clinical trial and allocated randomly to treatment with a single 
dose of ivermectin 100 mcg/kg, DEC 3 or DEC 6 mg/kg, or placebo, 
38 participated in the entomological study. For the present study of 
mortality rates, batches of laboratory-bred Ae. polynesiensis were 
blood-fed on 26 mf carriers (8,7,3 and 8 respectively were treated with 
ivermectin 100 mcg/kg, DEC 3 mg/kg, DEC 6 mg/kg and placebo). 
All mosquitoes were 3 days old when blood fed. At 1,3 and 6 months 
after treatment, one arm of each carrier was enclosed for 1 O- 15 
minutes in a cage of mosquitoes (range 672 to 1979 mosquitoes per 
cage, median 13 14). For the following 15 days the cages were stored at 
27-29 “C in a constant-temperature room. The 10% sucrose solution 
used for mosquito feeding was removed 18 h before the blood-meal. 
Every morning, from the 2nd to the 15th day after the blood-meal, both 
the numbers of “naturally-dead” mosquitoes and mosquitoes killed 
for dissection were recorded. On the 15th day, the surviving mosqui- 
toes were killed and numbered. 
The study was kept blind until 7 months after treat- 
ment, neither carriers, nor clinicians or, entomologists were aware of 
the nature of the drug administered. Cumulative survival probabilities 
were calculated by the life-table method (Laplanche et al., 1981). The 
overall differences between the life-table survival rates were estimated 
using the log-rank summary chi-square statistic (Peto et al., 1977). 
Results 
The main results of both the clinical and ento- 
mological studies have been reported elsewhere (Barbazan et 
al., 1990; Cartel et al., 1991). In the current study, the percent- 
ages of fed and unfed mosquitoes (less than 2% were unfed 
until the 3rd day after the blood-meal, all had taken a blood- 
meal by the 4th day) as well as the mean numbers of W. baiz- 
crofii larvae at different stages were similar in “naturally- 
dead” and in killed mosquitoes. The overall cumulative 
survival probabilities were significantly lower (p < 0.001) 
both in mosquitoes fed on carriers treated with single doses of 
microfilaricidal drug (either ivermectin or DEC) compared to 
those fed on placebo treated carriers. Survival was also lower 
in mosquitoes fed on ivermectin treated carriers compared to 
those fed on DEC treated carriers at 1, 3 and 6 months after 
treatment (fig. 1, 2 and 3). Nevertheless, because the DEC 6 
mg/kg and ivermectin 100 mcg/kg survival curves cross at 3 
months after treatment (fig. 2), caution has to be taken in inter- 
pretation. The cumulative mortality rates were roughly similar 
(about 90%) by the 15th day after blood-meal, in mosquitoes 
fed on carriers 1 month after they had been treated with either 
single dose of ivermectin or DEC (6  and 3 mg/kg); by com- 
parison, they were less than 20% by the same day after blood- 
*. 
‘ ORSTOM Fonds Documentaire 
344 Tsop. Mec/. Pmmitol. 42 (1991) J.-L. Cartel, Y. Secliari, A. Spiegel et al. - 
100 - 
post blood-meal days 
Fig. 1 Cumulative survival probabilities in Ae. polynesiensis fed on 
Wuchereria bancrofti carriers by one month after treatment with 
placebo, DEC and ivermectin single doses . 
Lo 
.g 60- 
50- 
$ 40- 
a 
30- 
U 
ar 
placebo 
DEC 3 mgAg 
DEC 6 mglkg 
2o t \ lvermectin 100 mc#kg 
lot 
04 I I I  I : : : : : : ! !  I : I  
O 1 2  3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5  
post blood-meal days 
Fig. 3 Cumulative survival probabilities in Ae. polynesiensis fed on 
W. bancrofti carriers by six months after treatment with placebo, 
DEC and ivermectin single doses 
meal in mosquitoes fed on carriers treated with placebo (table 
I). In mosquitoes fed on carriers 3 months after they had been 
treated with microfilaricidal drugs, cumulative mortality rates 
were still of 80% or more by the 15th day after blood-meal 
when they were of 26 % in mosquitoes fed on carriers treated 
by placebo. They were of 80% in mosquitoes fed on carriers 6 
months after they had been treated with ivermectin, signifi- 
cantly higher (p < 0.01) than in mosquitoes fed on carriers 
who had been treated with DEC (either at 6 or 3 mglkg). 
The summarized results of our study may be 
expressed as follows: ( I )  mortality rates were much higher in 
mosquitoes fed on carriers treated with microfilaricidal drugs 
than in those fed on placebo treated carriers and significantly 
higher in mosquitoes fed on ivermectin than on DEC treated 
carriers, (2)  they were roughly similar each day during the 15- 
day period following the blood-meal and (3) the phenomenon 
was observed up to 6 months after treatment though its inten- 
sity decreased with the passage of time. 
90 -. 
80 -_ 
g 70- 
60- 
E 50-  
p 40- 
'2 7 30-- 
20 -- 
I O - -  
- 
L .- 
E 
\ placebo 
DEC 3 mgkg 
lvermectin 
100 mc#kg 
DEC 6 mgAg 
o - l ! l I l ! ! I : : : l r ! : I  
O 1 2  3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5  
post blood-meal days 
Fig. 2 Cumulative survival probabilities in Ae. polynesiensis fed on 
W. bancrofti carriers by three months after treatment with placebo, 
DEC and ivermectin single doses. 
Discussion 
The efficacy of ivermectin in killing ecto- 
parasites in animals has been well established (Benz et al., 
1989; Soll, 1989). In a study conducted in Australia, ivermec- 
tin administered subcutaneously to cattle resulted in immedi- 
ate high mortality of Culicoides brevifarsis (Standfast et al., 
1984). More recently, acute toxicity and 100% mortality have 
been observed in Ae. aegypti, Ae. albopictus and Culex quiiique- 
fasciatus fed a blood-ivermectin mixture through a chick skin 
membrane (Tesh and Guzman, 1990). Nevertheless, to our 
knowledge, mortality has not been reported in insects fed 
either on animals or on humans such a long time after treat- 
ment as 1,3 or 6 months. In  the above studies, the death of in- 
sects was nearly 100% in the few days (1-2) following the 
blood-meal although in our study the daily mortality rate re- 
mained stable (about 8 %) over the 15-day period following the 
blood-meal. This is possibly due to the fact that, in the current 
study, mosquitoes were not fed on carriers immediately after 
treatment. Regarding DEC, its efficacy in reducing the trans- 
mission of filariasis by the vector mosquitoes was first re- 
ported by Laigret et al. (1965) on the basis of epidemiological 
analysis, and also from entomological studies (Chen and Fan, 
1977) but the reduction was attributed to the effect of DEC on 
the development of W. bancrofti larvae and not to the death of 
vectors. 
The reasons why a single dose of 100 mcg/kg 
ivermectin induced important mortality in mosquitoes fed on 
carriers several months after they had been treated remain dif- 
ficult to explain. It is known that, in humans treated with a 6 
mg dose, concentration of ivermectin peaks at 4 hours after the 
intake and that peak plasma concentration metabolites occur 
somewhat later (Fink and Porras, 1989). Concerning elimina- 
tion of ivermectin from the body fluids and tissues, it has been 
shown in rats that radioactive residues have practically disap- 
peared from blood at 4 days after treatment (Chiu and Lu, 
1989). Presently, to our knowledge, there is no evidence that 
residues of ivermectin or its metabolites could persist for 
months in humans and be the cause of death of biting insects. 
Same remarks apply to DEC which has been demonstrated, at 
dosage of I O  mg/kg, to provoke a peak blood concentration in  
I 
," 
A 
Trop. Med. Parasitol. 42 (1991) 345 - Gortali ty rates in Aedes polyzesiensis 
Table 1 Cumulative mortality rates at 8th and 15th days after blood-meal in Ae. polynesiensis fed on W. bancrofti carriers by 1, 3 and 6 
months after treatment with ivermectin, DEC, and placebo 
Post-treatment Post Cumulative mortality in mosquitoes fed on carriers treated with: 
months blood-meal days lvermectin DEC DEC Placebo 
100 mcglkg 6 mglkg 3 mg/kg 
1 
3 
8 
15 
8 
15 
76 % 
98 Yo 
53 Yo 
86 % 
55 % 
94 o/ó 
43% 
87 Yo 
49 % 
90% 
29 % 
79 % 
7 Yo 
17% 
18% 
26 % 
6 a 43% 19% 19% 14% 
15 80% 65 % 60 % 28 YO 
3 hours which decreases to zero within 48 hours (Mackenzie 
and Kron, 1985). Nevertheless, when considering the phe- 
nomenon we have reported and the decrease of its intensity 
with the passage of time, it might be speculated that drug re- 
sidues persist in tissues and affect mosquitoes when biting 
treated humans. Whatever the explanation, tlie death of 
mosquitoes feeding on treated populations, more especially 
on populations treated with ivermectin, may represent an ad- 
ditional advantage in filariasis control strategy. This finding 
should be taken into account when efficacy of mass treatments 
in filariasis control programmes is assessed not only on the 
evolution of microfilaremia in carriers but also on the trans- 
mission by the vector mosquitoes. Further studies are planned 
in French Polynesia to assess whether similar results are ob- 
served in Ae. polynesietzsis and in Ae. aegypti fed on W. ban- 
crojìi carriers as well as on non microfilaremic volunteers 
treated with single doses of either ivermectin or DEC. 
Acknowledgements 
This study received financial support from the 
UNDP/World Bank/WHO Special Programme for Research and 
Training inTropical Diseases (TDR). We are indebted to Merck Sharp 
and Dohme Research Laboratories for supplying the drugs used in this 
study. We acknowledge the technical assistance of Mr. M. Faaruia, R. 
Thirel, A. Tetuanui, L. Colombani and P. Tuhiti (Laboratory of Ento- 
mology ORSMTOM/Institut Malarde). 
References 
Cartel, J.-L., A. Spiegel, L. Nguyen, B. Genelle, J.-F. Roux: Double- 
blind study on efficacy ans safety of single doses of ivermectin and 
diethylcarbamazine for treatment of Polynesian Wuchereria ban- 
crofti carriers. Results at six months. Trop. Med. Parasitol. 42 
(1991)38-40 
Clten, C. C., P. C. Fan: The effect of diethylcarbamazine treatment on 
development of bancroftian microfilaremia in Culex fatigans. 
SouthEastAsian J.Trop.Med. Publ. Hlth. 8 (1977)53-55 
CKu, S. H. L., A. Y. H. Lu: Metabolism and tissue residues. in W. C. 
Campbell Edit. Springer-Verlag New York, Berlin, Heidelberg, 
London, Paris,Tokyo. Ivermectinand Abamectin (1989) 215-229 
Fink, D. W., A. G. Porras: Pharmacokinetics of ivermectin in animals' 
and humans, in W. C. Campbell Edit. Springer-Verlag New York, 
Berlin, Heidelberg, London, Paris, Tokyo. Ivermectin and 
Abamectin( 1989)215-229 
Laigret, J., J.  Kessel, L. Malardé, B. Banibridge, H. Adams: La lutte 
contre la filariose apériodique en Polynésie Française. Bull. Soc. 
Path. Exo. 58(1965) 895-916 
Laplanche, A., C. Coin-Noirgué, R. Flamant: Méthodes statistiques ap- 
pliquées àla recherche clinique. Ed. Flammarion (1987) Paris 
Mackenzie, C. D., M. A. Kron: Diethylcarbamazine: a review of its ac- 
tion in onchocerciasis, lymphatic filariasis and inflammation. 
Trop.Dis.Bull.82(1985) 1-37 
Peto, R., N. C. Pike, P. Arinitage: Design and analysis of randomized 
clinical trials requiring prolonged observation of each patient. Part 
2. Analysis and examples British J. Cancer 35 (1 977) 1-39 
Roux, J.-F., J.-L. Cartel, PII. Perolat, J.-P. Boutin, Y. Sechan, M. 
Larivière, M. A. Aziz: Etude de I'ivermectin pour le traitement de la 
filariose lymphatique dûe à Wuchereria bancrofti en Polynesie 
Francçaise. Bull. Soc. Path. Exo. 82 (1 989) 72-8 1 
Soll, M. D.: Use of Ivermectin in laboratory and exotic mammals and 
in birds, fishes and reptiles. In W. C. Campbell Edit. Springer-Ver- 
lag New York, Berlin, Heidelberg, London, Paris, Tokyo. Ivermec- 
tin andAbamectin( 1989) 264-265 B d " ,  Ph., Y. SecIran. J.-P. Boutin, A .  Spiegel, J.-L. Cartel. J.-F. 
dose treatments of Wucliereria bancrofiicarriers on transmission in 
vector Aedespolynesiensis. VIIth International Congress of Parasi- 
(1990) 1 I70 
Ben:, G. W., R. A. Roncalli. S. J. Gross: Use of ivermectin in cattle, 
sheep, goats and swine, in W. C. Campbell Edit. Springer-Verlag 
New York, Berlin, Heidelberg, London, Paris, Tokyo. Ivermectin 
andAbamectin( 1989)215-229 
Cartel, J.-L., Y. Sechan, J.-P. Bourin. Pli. Celerier, R. Plichart, J.-F. 
Rotfx: Ivermectin for treatment of bancroftian filariasis in French 
Polynesia efficacy in man, effect on transmission by vector Aedes 
polynesiensis.Trop. Med.Parasitol.41 (1990)241-244 
Standfast, A., J .  J .  Muller, D. D. w i ~ s o f ~ ~  Mortality of culicoides Roux: Effect of ivermectin and diethylcarbamazine (DECI single brevitarsis (Diptera: Ceratopogonidae) fed on cattle treated with 
ivermectin. J. Econ~Entomo1~77(1985)41g~42, 
TesIl, R. B., H. Guznlan: Mortality and infertility in adult mosquitoes toiofl. Abst 'Io c6. soc. Française 'PPI. 2. after the ingestion of blood containing ivermectin. Am. J. Trop. 
Med.Hyg.43(1990)229-233 
Jean-Louis Cartel 
Institut Territorial de Recherches Médicales Louis Malardé 
B. P. 30, Papeete 
Tahiti, Polynesie Francaise 


Cumulative mortality rates in Aedes polynesiensis after feeding on Polynesian Wuchereria bancrofti carriers treated with single doses of ivermectin, diethylcarbamazine and placebo

Cumulative mortality rates in Aedes polynesiensis after feeding on Polynesian Wuchereria bancrofti carriers treated with single doses of ivermectin, diethylcarbamazine and placebo

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