STUDIES OF FILARIASIS IN KEBAN AGUNG AND GUNUNG AGUNG VILLAGES IN SOUTH BENGKULU, SUMATERA, INDONESIA I11: Natural and artificial infections of vector mosquito species
Vol. XI1 No. I
1984
Bulletin Penetitian Kesehatan
(Health Studies in Indonesia)
STUDIES OF FILARIASIS IN KEBAN AGUNG AND GUNUNG AGUNG
VILLAGES IN SOUTH BENGKULU, SUMATERA, INDONESIA I11 :
Natural and artificial infections of vector mosquito species *
'
Sudomo, M.', Suwarto and Lim Boo ~ i a t ~
ABSTRACT
Sejumlah 13.133 nyamuk yang terdiri dari 4 species Mansonia spp dan 5.629 nyamuk yang terdiri
dun dua species Anopheles spp dari desa Keban Agung dun Gunung Agung telah dipenksa dengan jalan
pembedahan untuk mengetahui adanya infeksi larva Brugia, selama periode 24 bulan. Infeksi larva Brugia
pada nyamuk Mansonia spp lebih tinggi daripada pada nyamukAnopheles spp. Pada semua species nyamuk Mansonia pemah ditemukan mengundung larva Brugia stadium 3 (stadium infektifl sedangkan pada
Anopheles tidak pernah ditemukan larva Brugia stadium ini. Dalam percobmn penginfeksian dengan
penderita filariasis (B. rnalayi) dengan empat species Mansonia dun lima species Anopheles terbukti
bahwa semua species Mansonia rentan terhadap B. malayi sedangkan pada Anopheles hanya 2 species
yang d q a t d iinfeksi.
-
-
- -
--
INTRODU~ION
MATERIALS AND METHODS
Longitudinal studies were conducted on filariasis vectors following the survey on mosquito
fauna by Sudomo et al. 1983 in two filariasis
endemic areas in South Bengkulu. Suzuki et al.
(1981) in their preliminary survey of filariasis
vectors in the study areas, revealed several Mansonia spp. and some of the Anopheles spp. as potential vectors of Brugia malayi. The studies were
further extended for a 24 month period to
establish (1) seasonal variations of natural infection in mosquito vectors; (2) confirmation of
potential vectors, and (3) experimental infections
of various mosquito spp to assess the susceptibility of these mosquitoes to the parasite.
The study areas (Fig. 1) and the procedures of
the monthly routine nocturnal collections of
landing mosquitoes from indoors and outdoors
have been documented by Sudomo et al. (1983).
Most of the Mansonia and Anopheles spp. collected monthly were individually dissected to
examine for filariasis infection. Larvae collected
were mounted in glycerine and identified under
the compound microscope. The larvae were identified as Brugia sp. with the aid of the key by
Nelson (19601, and Rarnachandran (1970). They
were reconfirmed by Dr. Mak Joon Wah of Malaysia and Mr. Purnomo of Indonesia.
Nine mosquito species collected by light traps
at various periods from Keban Agung and Gunung
Agung villages were used for experimental
studies. They were sorted out and divided into
two batches, one for the experiments, a d
another for the control. ~h~ mosquitoes were
fed on four microfilariae (MF) carriers with 96,
84, g8 and 129 microfilariae per 20 mm3 blood.
After feeding, they were held in cages measuring
*
This study is supported by filariasis component of
the UNDP/World BankjWHO Special Programme
for Research and Training in ~ i o p i c a Diseases.
l
1. Health Ecology Research Centre, National Institute
of Health Research and Development, Ministry of
Health, P. 0 . Box 226, Jakarta, Indonesia.
2. WHO/Vector Bioloav and Control Research Unit11, P. 0 . BOX 302, Jakarta, Indonesia.
--
NATURAL AND ARTIFICIAL INFECTIONS OF VECTOR MOSQUITO SPECIES
Nipa palm
Swampy areas
Rice fields
secondary forest
(rubber)
Field station
Fig. 1. Map showing study areas in South Bengkulu, Sumatera, Indonesia.
45
SUDOMO, M. ET.AL.
In Gunung Agung 5,629 mosquitoes of the
same species as of Keban Agung were examined.
Of the four Mansonia spp. the lowest natural
infection rate was found in Ma. uniformis; Ma.
bonneae had the highest worm-load compared
t o all the other species. Like in Keban Agung
infection rates of An. nigerrimus and An. peditaeniatus were very low, and no infective-stage
Brugia larvae was found. (Table 2).
Nine mosquito species were used for experimental infections, and results are presented
in Table 3. Of the four Mansonia spp. higher
success of infection rates were shown in Ma.
bonneae, Ma. dives and Ma. uniformis than in
Ma. annulata. However, there was no marked
difference shown in the development of Mf
t o infective stage larvae among the four Mansonia spp. Ma. uniformis was found with higher
worm-load of Brugia 3rd stage larvae than the
other species, and the lowest was found in Ma.
annulata. In the controls only one mosquito of
Ma. bonneae and Ma. dives was found with one
3rd stage Brugia larvae each at 13.5 days. For
Anopheles species only An. peditaeniatus and
An. nigerrimus were found to take the infection, however development of Mf to 3 rd stage
larvae was found to be very low as compared
t o Mapspnia species. In the control, one mosquita/20f An, peditaeniatus and An. nigerrimus
which died at 6 days and 4 days respectively
30 cm3 and fed with sugar water only. The holding period for these mosquitoes was up to 13.5
days, and any mosquito which died during the
holding period was dissected. Survivors were
sacrified at the end of the period. The holding
period was based on Suzuki et al. (1981) who
showed that the Mf development to infective
stage larvae in the mosquitoes were from 7.5 13.5 days.
Equal numbers of mosquitoes for each of
the species were used as controls. These mosquitoes were kept in identical cages separately,
and at the same time. The same procedures
were used for the control mosquitoes as that
of the experimental ones, except that these
mosquitoes were fed with sugar water only.
RESULTS
A total of 13.133 mosquitoes comprising
four Mansonia spp. and two Anopheles spp.
were examined from Keban Agung, and results
are shown in Table 1. Among the four Mansonia spp.,Ma. bonneae and Ma. dives \r/ found
with a higher natural infection rate and wormload than Ma. uniformis or Ma. annulata. The
natural infection rates of An. peditaeniatus and
An. nigemmus was exceptionally low, but
none of them were found harboring infectivestage Brugia larvae.
Table 1. Natural infection with filarial larvae of lahding mosquito species from indoors and
outdoors collections combined in Keban Agung village at South Bengkulu, Sumatera.
Mosquitoes species
Ma. bonneae
Ma. dives
Ma. uniforrnis
Ma. annulata
An. peditaeniatus
An. nigerrimus
*
No. of
mosquitoes
examined
2404
1377
1794
3376
2855
1327
%
positive
%with
infective
larvae
0.54
0.65
0.28
0.21
0
0
1.25
1.23
0.72
0.50
0.14
0.45
Less than 10 infected mosquitoes.
46
Total
number
of larvae
124
71
61
51
5
7
Mean no. larvae per
infected mosquito
1 st & 2nd
3rd
stage
stage
5.47 f 2.98
4.29 f 2.49
3.77 f2.58
2.24f 1.72
1.25*
1.16*
3.38 f 0.28
2.78 f 1.52
2.4 f 1.14
1.86 f 1.22
-
NATURAL AND ARTIFICIAL INFECTIONS OF VECTOR MOSQUITO SPECIES
Table 2. Natural infection with filarial larvae of landing mosquito species from indoors and outdoors
collections combined in Gunung Agung village at South Bengkulu, Sumatera.
No. of
mosquitoes
examined
Mosquito species
%
positive
Mean no. latvae per
infected mosquito
Total
number
of larvae
%with
infective
larvae
3rd
Stage
1st & 2nd
stage
* Less than
1.31
1.61
0.77
1.08
0.58
0.79
1910
871
520
1015
686
627
Ma. bonneae
Ma. dives
Ma. uniformis
Ma. annulata
An. peditaeniaius
An. nigerrimus
0.73
0.69
0.58
0.49
0
0
5.45 k3.36
2.92 f 1.94
1.5'
2.0 k0.95.
1.75*
1.6 *
107
50
10
30
7
8
'
3.36 k 1.78
1.5
0.84
1 .3*
1.6 k0.8
+
-
-
10 infected mosquitoes.
Table 3. Percentage of development of M f to infective stage larvae (3rd stage) in various mosquito species
'from 0.5 13.5 days in experimental infection and mean number of larvae per infected mosquito.
-
I
Mosquito
species
No.of %
mosq. positested tive larvae
'I-
-
Experimental infections
YOdevelop- '
Mean larvae per
infected mosquito
2;
Ma. bonneae
Ma. dives
Ma. uniformis
Ma. annulata
An. peditaeniatus
An. nigerrimus
An. vagus
An. philippinensis
Coq. nigrosignata
240
170
120
180
180
60
20
20
40
993
746
621
256
842
38
O
O
0
40.8
42.9
36.7
19.4
29.9
30
0
0
0
n = Numberdissected;
* C =
Brugia sp.
+
=
TL:iF
1
3rd
stage
To , l s t 2nd
lst&
3rd
stages
2nd
stages
stages
65.3
63.8
67.6
69.1
99.5
94.7
-
34.1 6.61 k3.12
36.2 6.52 13.85
32.4 10.92 k4.15
30.9 5.05k2.82
0.5 16.1 1 56.45
5.3 2.0 k0.55
-
I
Number positive;
=
3.52 f0.56
3.69 k0.71
4.56 k0.92
2.25k0.44
0.07 '
0.1 1 *
-
-
Control
Died at
2-4
mas- days
quin
+
toes
NO.
of
240
170
120
180
180
60
20
20
40
-
42
31
28
38
35
8
6
2
9
Died at
5-8
days
n
49
0
34
0
32
0
55
0
48
0
15
1
6
0
8
0
lx 11
+
Sacrified
at 13.5
days
n
+
149 1
0
105 0
0
0
60 1 "1
87 0
0
1
97 3X
37 lX
0
8 0
0
0
100
lx 20 2X
Less than 10 individuals;
x = Dirofilariaspp.
was found with one Brugia larvae each, and of
those that were sacrified at 13.5 days, three of
the former and one of the latter were found
with 7 and 2 Dirofilaria larvae. None of the
An. vagus, An. philippinensis and Coq. nigrosignata used Were infected. In the control group,
few Coq. nigrosignata which either died or
sacrified were found with DiroJilaria larvae only.
For the purpose of analyses, the natural infection in all Mansonia spp. were considered
together. Correlation-coefficient tests show
that there was no correlation between monthly
infection and infectivity rates in the four mosquito species with either density or rainfall. It
is however significant that the estimated number
of infective Mansonia spp. averaged at 0.03 per
.
SUDOMO M. ET.AL.
man hour (range 0.024 t o 0.092) in Keban
Agung and 0.036 (range 0.022 t o 0.101) in Gunung Agung (Fig. 2). The estimation of the
infection and infectivity rates of the four Mansonia spp. revealed a high infective rates in almost
all months during the year particularly in Keban
Agung and t o a lesser degree in Gunung Agung.
DISCUSSION
The present studies on natural infection and
susceptibility of filariasis vectors a t Keban and
Gunung Agung, Bengkulu show that four Mansonia spp. are good vectors of Brugia filariasis
in the areas. The higher mean worm-load of
Keban Agung
.-.--.--*infection
Gunung Agung
17
4 - -
1980
---
+ .
f
-----
1981 -
^ -
*
Fig. 2. Estimated number of infected and infective Mansonia spp. per man-hour
1982
NATURAL AND ARTIFICIAL INFECTIONS OF VECTOR MOSQUITO SPECIES
Brugia larvae in Ma. bonneae and Ma. dives found
in natural infections was also reflected in
experimental infections with these two species
being higher than in Ma. annulata. The mean
worm-load in naturally infected Ma. uniformis
was lower than Ma. bonneae and Ma. dives;
however experimentally, Ma. uniformis was
found to be highly susceptible. It is therefore
concluded that among the four Mansonia species, Ma. bonneae, Ma. dives and Ma. uniformis
are more efficient vectors than Ma. annulata.
The present findings further support the preliminary observations by Suzuki et al. (1981) on
these four species as the principal vectors of
periodic B, malayi in the study areas.
A very low rate of natural infection with
brugian larvae was found in An. peditaeniatus
and An, nigerrimus, but no 3rdstage larvae were
detected in them. Experimentally, these mosquitoes were found to take the infection very
well, but the percentage with development of
Mf to infective stage larvae was negligibly low.
Suzuki et al. (1981) examined 1517 An. hyrcanus group (=An. peditaeniatus and An. nigerrimus) but found none of them was naturally
infected; however, experimentally they showed
that the Mf could develop to 3rd-stage larvae, 8%
days onward after feeding on Mf carriers. It was
most unfortunate that during these experimental
infections with both Mansonia and Anopheles
spp. there were no control experiments. Thus it
is quite likely that the 3rd-stage brugian larvae
found in these two mosquitoes may be due to
natural infection. As B. pahangi is prevalent
among the domestic cats in the study area (Suzuki et al., 1981; Lim & Sudomo (in press) there
is a likelyhood that the 3rd-stage larvae found
in their experiments could be B. pahangi. None
of the An. vagus, An. philippinensis and Coq.
nigrosignata .used in these experiments were
found to take the infection. Based on the present
studies, it is unlikely that Anopheles spp. may
play a significant role in the B. malayi transmission in the study areas.
In conclusion it was apparent from the experimental and natural infection results that the
four Mansonia spp. are the principle vectors of
B. malayi with Ma. bonneae and Ma. dives being
more efficient vectors than Ma. uniformis and
Ma. annulata. Considering the estimation of high
infective numbers of these mosquitoes and the
total number of bites per man as received over
a period, the role of Mansonia spp. in the transmission of B. malayi on these two areas cannot
be over emphasized. Although the infective
larvae of different Bmgia spp. are morphologically indistinguishable, experimental evidence
obtained, corroborates this view.
SUMMARY
A total of 13,133 and 5,629 mosquitoes
comprising of four Mansonia spp. and two Anopheles spp. was examined for natural infection
with Bmgia larvae in both Keban Agung and Gunung Agung villages, Sumatera for a 24 month
period. The natural infection rates of Mansonia
spp. were significantly higher than the Anopheles spp. All the Mansonia spp. were found with
infective stage Brugia larvae as compared t o
none found in the Anopheles spp.
Experimental infections with four Mansonia
spp. and five Anopheles spp. to microfilariae
carriers show that all the four Mansonia spp.
were susceptible while only two of the five Anopheles spp. took the infections.
The natural and experimental infections of
all the four Mansonia spp. were found t o be
naturally efficient and successful experimental
vectors of B. malayi. It is, thus concluded that
the Mansonia spp. are the principle vectors of
B. malayi transmission in both the study areas.
ACKNOWLEDGEMENTS
The authors are grateful to the field staff,
National Institute of Health Research and Development (NIHED) Jakarta, and also t o Dr. E.
Oswari, Director of Health Services, Bengkulu
and Dr. Abu Hanifah, Chief, CDC/Bengkulu,
for their supports. Thanks are also due to Dr.
N, G. Gratz, Director, VBC, Geneva, Dr. C. P.
Pant, Chief, ECV, Geneva for their criticisms,
and Dr. Y. H. Bang, Project Leader, VBCRU2 Jakarta for his support.
They are also grateful t o Dr. P. K. Rajagopalan, Vector Control Research Centre, Pondi-
SUDOMO ,M. ET. AL.
cherry, India, for his advice; Dr. Mak Joon Wah,
Filariasis Division, Institute for Medical Research, Kuala Lumpur, Malaysia and t o Mr. Pur-
nomo, Staff of the Navy Medical Research Unit,
Jakarta, Indonesia for their confirmation of the
Bmgia larvae in the vectors.
REFERENCES
I;im Boo Liat and M. Sudomo (in manuscript).
Studies of filariasis in Keban Agung and Gunung Agung villages in South Bengkulu,
Sumatera V: Animal fiiariasis.
Nelson, G.A. (1960). The identification of filarial larvae in their vectors. Indian J. Mariology, 14 : 585-592.
Ramachandran, C.P. (1970). A guide to methods
and technique in filariasis investigation. Institu te for Medical Research Bulletin, Kuala
Lumpur No. 15 : 39 pp.
Sudomo, M., Suwarto and Lim Boo Liat (1983).
Studies of Filariasis in Keban Agung and Gunung Agung villages in South Bengkulu, Sumatera, Indonesia : I. The mosquito fauna
with reference to seasonal studies of two Anopheles and Culex tntaeniorhynchus. Bull.
Health Studies in Indonesia XI. 1 : 25-35
Suzuki, T., M. Sudomo, Y.H. Bang and Lim Boo
Liat (1981). Studies on malayan fiariasis
in Bengkulu (Sumatera), Indonesia with
special reference t o vector confirmation.
Southeast Asian J. Trop. Med. Pub. Hlth. 12 :
47-54.
1984
Bulletin Penetitian Kesehatan
(Health Studies in Indonesia)
STUDIES OF FILARIASIS IN KEBAN AGUNG AND GUNUNG AGUNG
VILLAGES IN SOUTH BENGKULU, SUMATERA, INDONESIA I11 :
Natural and artificial infections of vector mosquito species *
'
Sudomo, M.', Suwarto and Lim Boo ~ i a t ~
ABSTRACT
Sejumlah 13.133 nyamuk yang terdiri dari 4 species Mansonia spp dan 5.629 nyamuk yang terdiri
dun dua species Anopheles spp dari desa Keban Agung dun Gunung Agung telah dipenksa dengan jalan
pembedahan untuk mengetahui adanya infeksi larva Brugia, selama periode 24 bulan. Infeksi larva Brugia
pada nyamuk Mansonia spp lebih tinggi daripada pada nyamukAnopheles spp. Pada semua species nyamuk Mansonia pemah ditemukan mengundung larva Brugia stadium 3 (stadium infektifl sedangkan pada
Anopheles tidak pernah ditemukan larva Brugia stadium ini. Dalam percobmn penginfeksian dengan
penderita filariasis (B. rnalayi) dengan empat species Mansonia dun lima species Anopheles terbukti
bahwa semua species Mansonia rentan terhadap B. malayi sedangkan pada Anopheles hanya 2 species
yang d q a t d iinfeksi.
-
-
- -
--
INTRODU~ION
MATERIALS AND METHODS
Longitudinal studies were conducted on filariasis vectors following the survey on mosquito
fauna by Sudomo et al. 1983 in two filariasis
endemic areas in South Bengkulu. Suzuki et al.
(1981) in their preliminary survey of filariasis
vectors in the study areas, revealed several Mansonia spp. and some of the Anopheles spp. as potential vectors of Brugia malayi. The studies were
further extended for a 24 month period to
establish (1) seasonal variations of natural infection in mosquito vectors; (2) confirmation of
potential vectors, and (3) experimental infections
of various mosquito spp to assess the susceptibility of these mosquitoes to the parasite.
The study areas (Fig. 1) and the procedures of
the monthly routine nocturnal collections of
landing mosquitoes from indoors and outdoors
have been documented by Sudomo et al. (1983).
Most of the Mansonia and Anopheles spp. collected monthly were individually dissected to
examine for filariasis infection. Larvae collected
were mounted in glycerine and identified under
the compound microscope. The larvae were identified as Brugia sp. with the aid of the key by
Nelson (19601, and Rarnachandran (1970). They
were reconfirmed by Dr. Mak Joon Wah of Malaysia and Mr. Purnomo of Indonesia.
Nine mosquito species collected by light traps
at various periods from Keban Agung and Gunung
Agung villages were used for experimental
studies. They were sorted out and divided into
two batches, one for the experiments, a d
another for the control. ~h~ mosquitoes were
fed on four microfilariae (MF) carriers with 96,
84, g8 and 129 microfilariae per 20 mm3 blood.
After feeding, they were held in cages measuring
*
This study is supported by filariasis component of
the UNDP/World BankjWHO Special Programme
for Research and Training in ~ i o p i c a Diseases.
l
1. Health Ecology Research Centre, National Institute
of Health Research and Development, Ministry of
Health, P. 0 . Box 226, Jakarta, Indonesia.
2. WHO/Vector Bioloav and Control Research Unit11, P. 0 . BOX 302, Jakarta, Indonesia.
--
NATURAL AND ARTIFICIAL INFECTIONS OF VECTOR MOSQUITO SPECIES
Nipa palm
Swampy areas
Rice fields
secondary forest
(rubber)
Field station
Fig. 1. Map showing study areas in South Bengkulu, Sumatera, Indonesia.
45
SUDOMO, M. ET.AL.
In Gunung Agung 5,629 mosquitoes of the
same species as of Keban Agung were examined.
Of the four Mansonia spp. the lowest natural
infection rate was found in Ma. uniformis; Ma.
bonneae had the highest worm-load compared
t o all the other species. Like in Keban Agung
infection rates of An. nigerrimus and An. peditaeniatus were very low, and no infective-stage
Brugia larvae was found. (Table 2).
Nine mosquito species were used for experimental infections, and results are presented
in Table 3. Of the four Mansonia spp. higher
success of infection rates were shown in Ma.
bonneae, Ma. dives and Ma. uniformis than in
Ma. annulata. However, there was no marked
difference shown in the development of Mf
t o infective stage larvae among the four Mansonia spp. Ma. uniformis was found with higher
worm-load of Brugia 3rd stage larvae than the
other species, and the lowest was found in Ma.
annulata. In the controls only one mosquito of
Ma. bonneae and Ma. dives was found with one
3rd stage Brugia larvae each at 13.5 days. For
Anopheles species only An. peditaeniatus and
An. nigerrimus were found to take the infection, however development of Mf to 3 rd stage
larvae was found to be very low as compared
t o Mapspnia species. In the control, one mosquita/20f An, peditaeniatus and An. nigerrimus
which died at 6 days and 4 days respectively
30 cm3 and fed with sugar water only. The holding period for these mosquitoes was up to 13.5
days, and any mosquito which died during the
holding period was dissected. Survivors were
sacrified at the end of the period. The holding
period was based on Suzuki et al. (1981) who
showed that the Mf development to infective
stage larvae in the mosquitoes were from 7.5 13.5 days.
Equal numbers of mosquitoes for each of
the species were used as controls. These mosquitoes were kept in identical cages separately,
and at the same time. The same procedures
were used for the control mosquitoes as that
of the experimental ones, except that these
mosquitoes were fed with sugar water only.
RESULTS
A total of 13.133 mosquitoes comprising
four Mansonia spp. and two Anopheles spp.
were examined from Keban Agung, and results
are shown in Table 1. Among the four Mansonia spp.,Ma. bonneae and Ma. dives \r/ found
with a higher natural infection rate and wormload than Ma. uniformis or Ma. annulata. The
natural infection rates of An. peditaeniatus and
An. nigemmus was exceptionally low, but
none of them were found harboring infectivestage Brugia larvae.
Table 1. Natural infection with filarial larvae of lahding mosquito species from indoors and
outdoors collections combined in Keban Agung village at South Bengkulu, Sumatera.
Mosquitoes species
Ma. bonneae
Ma. dives
Ma. uniforrnis
Ma. annulata
An. peditaeniatus
An. nigerrimus
*
No. of
mosquitoes
examined
2404
1377
1794
3376
2855
1327
%
positive
%with
infective
larvae
0.54
0.65
0.28
0.21
0
0
1.25
1.23
0.72
0.50
0.14
0.45
Less than 10 infected mosquitoes.
46
Total
number
of larvae
124
71
61
51
5
7
Mean no. larvae per
infected mosquito
1 st & 2nd
3rd
stage
stage
5.47 f 2.98
4.29 f 2.49
3.77 f2.58
2.24f 1.72
1.25*
1.16*
3.38 f 0.28
2.78 f 1.52
2.4 f 1.14
1.86 f 1.22
-
NATURAL AND ARTIFICIAL INFECTIONS OF VECTOR MOSQUITO SPECIES
Table 2. Natural infection with filarial larvae of landing mosquito species from indoors and outdoors
collections combined in Gunung Agung village at South Bengkulu, Sumatera.
No. of
mosquitoes
examined
Mosquito species
%
positive
Mean no. latvae per
infected mosquito
Total
number
of larvae
%with
infective
larvae
3rd
Stage
1st & 2nd
stage
* Less than
1.31
1.61
0.77
1.08
0.58
0.79
1910
871
520
1015
686
627
Ma. bonneae
Ma. dives
Ma. uniformis
Ma. annulata
An. peditaeniaius
An. nigerrimus
0.73
0.69
0.58
0.49
0
0
5.45 k3.36
2.92 f 1.94
1.5'
2.0 k0.95.
1.75*
1.6 *
107
50
10
30
7
8
'
3.36 k 1.78
1.5
0.84
1 .3*
1.6 k0.8
+
-
-
10 infected mosquitoes.
Table 3. Percentage of development of M f to infective stage larvae (3rd stage) in various mosquito species
'from 0.5 13.5 days in experimental infection and mean number of larvae per infected mosquito.
-
I
Mosquito
species
No.of %
mosq. positested tive larvae
'I-
-
Experimental infections
YOdevelop- '
Mean larvae per
infected mosquito
2;
Ma. bonneae
Ma. dives
Ma. uniformis
Ma. annulata
An. peditaeniatus
An. nigerrimus
An. vagus
An. philippinensis
Coq. nigrosignata
240
170
120
180
180
60
20
20
40
993
746
621
256
842
38
O
O
0
40.8
42.9
36.7
19.4
29.9
30
0
0
0
n = Numberdissected;
* C =
Brugia sp.
+
=
TL:iF
1
3rd
stage
To , l s t 2nd
lst&
3rd
stages
2nd
stages
stages
65.3
63.8
67.6
69.1
99.5
94.7
-
34.1 6.61 k3.12
36.2 6.52 13.85
32.4 10.92 k4.15
30.9 5.05k2.82
0.5 16.1 1 56.45
5.3 2.0 k0.55
-
I
Number positive;
=
3.52 f0.56
3.69 k0.71
4.56 k0.92
2.25k0.44
0.07 '
0.1 1 *
-
-
Control
Died at
2-4
mas- days
quin
+
toes
NO.
of
240
170
120
180
180
60
20
20
40
-
42
31
28
38
35
8
6
2
9
Died at
5-8
days
n
49
0
34
0
32
0
55
0
48
0
15
1
6
0
8
0
lx 11
+
Sacrified
at 13.5
days
n
+
149 1
0
105 0
0
0
60 1 "1
87 0
0
1
97 3X
37 lX
0
8 0
0
0
100
lx 20 2X
Less than 10 individuals;
x = Dirofilariaspp.
was found with one Brugia larvae each, and of
those that were sacrified at 13.5 days, three of
the former and one of the latter were found
with 7 and 2 Dirofilaria larvae. None of the
An. vagus, An. philippinensis and Coq. nigrosignata used Were infected. In the control group,
few Coq. nigrosignata which either died or
sacrified were found with DiroJilaria larvae only.
For the purpose of analyses, the natural infection in all Mansonia spp. were considered
together. Correlation-coefficient tests show
that there was no correlation between monthly
infection and infectivity rates in the four mosquito species with either density or rainfall. It
is however significant that the estimated number
of infective Mansonia spp. averaged at 0.03 per
.
SUDOMO M. ET.AL.
man hour (range 0.024 t o 0.092) in Keban
Agung and 0.036 (range 0.022 t o 0.101) in Gunung Agung (Fig. 2). The estimation of the
infection and infectivity rates of the four Mansonia spp. revealed a high infective rates in almost
all months during the year particularly in Keban
Agung and t o a lesser degree in Gunung Agung.
DISCUSSION
The present studies on natural infection and
susceptibility of filariasis vectors a t Keban and
Gunung Agung, Bengkulu show that four Mansonia spp. are good vectors of Brugia filariasis
in the areas. The higher mean worm-load of
Keban Agung
.-.--.--*infection
Gunung Agung
17
4 - -
1980
---
+ .
f
-----
1981 -
^ -
*
Fig. 2. Estimated number of infected and infective Mansonia spp. per man-hour
1982
NATURAL AND ARTIFICIAL INFECTIONS OF VECTOR MOSQUITO SPECIES
Brugia larvae in Ma. bonneae and Ma. dives found
in natural infections was also reflected in
experimental infections with these two species
being higher than in Ma. annulata. The mean
worm-load in naturally infected Ma. uniformis
was lower than Ma. bonneae and Ma. dives;
however experimentally, Ma. uniformis was
found to be highly susceptible. It is therefore
concluded that among the four Mansonia species, Ma. bonneae, Ma. dives and Ma. uniformis
are more efficient vectors than Ma. annulata.
The present findings further support the preliminary observations by Suzuki et al. (1981) on
these four species as the principal vectors of
periodic B, malayi in the study areas.
A very low rate of natural infection with
brugian larvae was found in An. peditaeniatus
and An, nigerrimus, but no 3rdstage larvae were
detected in them. Experimentally, these mosquitoes were found to take the infection very
well, but the percentage with development of
Mf to infective stage larvae was negligibly low.
Suzuki et al. (1981) examined 1517 An. hyrcanus group (=An. peditaeniatus and An. nigerrimus) but found none of them was naturally
infected; however, experimentally they showed
that the Mf could develop to 3rd-stage larvae, 8%
days onward after feeding on Mf carriers. It was
most unfortunate that during these experimental
infections with both Mansonia and Anopheles
spp. there were no control experiments. Thus it
is quite likely that the 3rd-stage brugian larvae
found in these two mosquitoes may be due to
natural infection. As B. pahangi is prevalent
among the domestic cats in the study area (Suzuki et al., 1981; Lim & Sudomo (in press) there
is a likelyhood that the 3rd-stage larvae found
in their experiments could be B. pahangi. None
of the An. vagus, An. philippinensis and Coq.
nigrosignata .used in these experiments were
found to take the infection. Based on the present
studies, it is unlikely that Anopheles spp. may
play a significant role in the B. malayi transmission in the study areas.
In conclusion it was apparent from the experimental and natural infection results that the
four Mansonia spp. are the principle vectors of
B. malayi with Ma. bonneae and Ma. dives being
more efficient vectors than Ma. uniformis and
Ma. annulata. Considering the estimation of high
infective numbers of these mosquitoes and the
total number of bites per man as received over
a period, the role of Mansonia spp. in the transmission of B. malayi on these two areas cannot
be over emphasized. Although the infective
larvae of different Bmgia spp. are morphologically indistinguishable, experimental evidence
obtained, corroborates this view.
SUMMARY
A total of 13,133 and 5,629 mosquitoes
comprising of four Mansonia spp. and two Anopheles spp. was examined for natural infection
with Bmgia larvae in both Keban Agung and Gunung Agung villages, Sumatera for a 24 month
period. The natural infection rates of Mansonia
spp. were significantly higher than the Anopheles spp. All the Mansonia spp. were found with
infective stage Brugia larvae as compared t o
none found in the Anopheles spp.
Experimental infections with four Mansonia
spp. and five Anopheles spp. to microfilariae
carriers show that all the four Mansonia spp.
were susceptible while only two of the five Anopheles spp. took the infections.
The natural and experimental infections of
all the four Mansonia spp. were found t o be
naturally efficient and successful experimental
vectors of B. malayi. It is, thus concluded that
the Mansonia spp. are the principle vectors of
B. malayi transmission in both the study areas.
ACKNOWLEDGEMENTS
The authors are grateful to the field staff,
National Institute of Health Research and Development (NIHED) Jakarta, and also t o Dr. E.
Oswari, Director of Health Services, Bengkulu
and Dr. Abu Hanifah, Chief, CDC/Bengkulu,
for their supports. Thanks are also due to Dr.
N, G. Gratz, Director, VBC, Geneva, Dr. C. P.
Pant, Chief, ECV, Geneva for their criticisms,
and Dr. Y. H. Bang, Project Leader, VBCRU2 Jakarta for his support.
They are also grateful t o Dr. P. K. Rajagopalan, Vector Control Research Centre, Pondi-
SUDOMO ,M. ET. AL.
cherry, India, for his advice; Dr. Mak Joon Wah,
Filariasis Division, Institute for Medical Research, Kuala Lumpur, Malaysia and t o Mr. Pur-
nomo, Staff of the Navy Medical Research Unit,
Jakarta, Indonesia for their confirmation of the
Bmgia larvae in the vectors.
REFERENCES
I;im Boo Liat and M. Sudomo (in manuscript).
Studies of filariasis in Keban Agung and Gunung Agung villages in South Bengkulu,
Sumatera V: Animal fiiariasis.
Nelson, G.A. (1960). The identification of filarial larvae in their vectors. Indian J. Mariology, 14 : 585-592.
Ramachandran, C.P. (1970). A guide to methods
and technique in filariasis investigation. Institu te for Medical Research Bulletin, Kuala
Lumpur No. 15 : 39 pp.
Sudomo, M., Suwarto and Lim Boo Liat (1983).
Studies of Filariasis in Keban Agung and Gunung Agung villages in South Bengkulu, Sumatera, Indonesia : I. The mosquito fauna
with reference to seasonal studies of two Anopheles and Culex tntaeniorhynchus. Bull.
Health Studies in Indonesia XI. 1 : 25-35
Suzuki, T., M. Sudomo, Y.H. Bang and Lim Boo
Liat (1981). Studies on malayan fiariasis
in Bengkulu (Sumatera), Indonesia with
special reference t o vector confirmation.
Southeast Asian J. Trop. Med. Pub. Hlth. 12 :
47-54.