Studies on bionomics of microfilaria of brugia malayi and dirofilaria immitis in Korea
Though the filariasis is one of the main mosquito-borne endemic disease in Korea,
the vector species of mosquitoes has not yet been clearly differentiated. The
present study is designed to supplement the knowledge of the behavior or bionomics
of microfilariae of Brugia malayi(B. malay) and Dirofilaria immitis (D.immitis) in
the host animals and in the possible vector mosquitoes caught in the endemic areas
and, in addition, several bionomical studies of these microfilariae were carried
out in vitro or in vivo.
The methods and materials used and the results in this study are summarized.
Materials and Methods
1. Mosquito collection: The investigators collected mosqutoes from cow stables or
indoors in endemic areas of human filariasis inculding Cheju-Do and Yongju, and an
area of dog filariasis, Chinju.
The mosquitoes caught were brought to the laboratory, identified and dissected
under the microscope to examine the filarial larvae in them.
2. Mosquito rearing: The larvae of mosquitoes were collected from the field and
brought to the laboratory to be reared at room temperature(26°±2℃).
After emergence, the female adult mosquitoes were fed on a dog infected with
D.immitis, and the development of the microfilariae in the mosquitoes was observed
day by day.
3. Viability of the infective larvae in the environmental media: The infective
larvae escaped from the proboscis of the infected mosquitoes were placed into
saline, distilled water, well water and serum or a blood cell suspension of human
and dog blood in saline solution, and the motility and morphological change were
4. Life span of the microfilariae: Blood infected with D.immitis was transfused
to non-infected healthy dog. The number of microfilariae in 0.02ml. of blood of the
dog transfused with infective blood was examined at intervals of 4-7 days after the
transfusion until the disappearance of all microfilariae from the blood.
5. Periodicity of microfilariae in the peripheral blood: Peripheral blood was
taken every three hours from the infected human and dog, and the number of
microfilariae in 0.02ml. of blood was checked.
6. Provocation test of microfilariae in the peripheral blood: Diethylcarbamazine
citrate (Supatonin, Tanabe) 3mg/kg, was given one time only to the filariasis and
elephantiasis cases. The microfilariae was checked before and 20 minutes after the
7. Phototaxis of the microfilarise: The blood which contained the microfilaria of
D.immitis was introduced into a slender glass tube, 2.5mm in diameter on the
surface of which 5cm. of black enamel alternated with 5cm. of unenameled area.
Both ends of the tube were sealed with vaseline. The tubes were placed in a water
bath of 10℃ and 36℃, and exposed to direct sun-light for the study of the
behavior of the microfilariae.
The mosquitoes collected from the endemic areas of filariasis were as follows:
Anopheles sinensis, A.sineroides, Culex pipiens, C.tritaeniorhynchus, C.sinenis,
C.orientalis, C.hayashii, C.vagans, Aedes vexans, Ae.koreicus, Ae.albopictus,
Ae.togoi, Ae.japonicus, Ae.esoensis and other unclassified Aedes sp.
Anopheles sinensis and Culex pipiens in inland and Aedes togoi and Aedes
albopictus in Cheju-Do (island) were predominant.
No larvae of filaria species could be found from the dissected mosquitoes which
were caught at the endemic area. It was observed that the microfilaria of D.immitis
fed by mosquitoes (Aedes Koreicus, Aedes albopictus) developed to infective stage
within 2-3 weeks. The infective larvae which emerged from the proboscis of the
mosquitoes into the water were observed to be able to survive for an hour.
The microfilariae placed into the slender tube in the water bath under the
exposure of sunlight showed that the microfilariae were gathered in large number at
the enameled dark portion but there were no sign of temperature influence on
travelling of the microfilaria at temperature difference between 10° and 36℃.
The nocturnal periodicity of microfilariae of both B.malayi and D.immitis in the
hosts was observed and showed peaks at the period of 23-24 o'clock for B.malayi and
at 00-01 o'clock in d.immitis.
The microfilariae in the viscera of the host showed no significant changes
following the administration of Diethylcarbamazine citrate.
The microfilariae introduced by blood transfusion into the non-infected healthy
host were able to survive up to 105 days.
Since Senoo (1951) and others have reported that the species of human filaria in
Korea was B.malayi, many workers have reported several endemic areas of B.malyai in
Korea. Although no vector mosquitoes of the filariasis have as yet been
differentiated in this study, Anopheles sinensis, Culex pipiens, Aedes togoi and
Aedes albopictus have been suspected as vectors by some previous workers.
Fourteen specles of mosqultoes including Anopheles, Culex and Aedes were
collected during the mosquito season in the endemic areas such as Yongju, Chinju
and Cheju-Do. The predominant species were Anopheles sinensis and Culex pipiens in
the inland but Aedes togoi were in the island of Cheju-Do.
The development of the microfilariae of D.immitis in the mosquitoes was observed
and Aedes Koreicus appeared to be the possible vector mosquitoes of D.immitis.
Though the nocturnal periodicity of both B.malayi and D.immitis was confirmed by
many workers, the peak density of the microfilariemia in the present study was
between 23-24 o'clock in B.malayi
Although Katamine (1952) observed the increased microfilariae of Wuchereria
bancrofli in peripheral blood after the administration of Deithylcarbamazine, the
result of the present provocation test showed no difference in the number of
microfilariemia before and after the administration of the same drug. This suggests
that there might be some complex biological difference between these two filaria
The microfilaria of D.immitis showed negative phototaxis in the present study.
This fact may supplement that of the nocturnal periodicity of microfilaria.
High fever and other side actions were observed after the administration of
diethylcarbamazine in filasiasis but these side reactions were decreased after
repeated administration of the drug.
The side reactions appeared to be caused by a pyrogenic substance coming from
dead microfilariae of D.immitis which were transfused into non-infected healthy dog
which was able to survive up to 105 days, although Wong (1964) observed that the
microfilariae introduced in a non-infected healthy dog were found in the peripheral
blood until 11-43 days after the transfusion of the infected blood.
About two third of the larvae disappeared within 34 days after the transfusion.
this indicates that life-span of larvae is not long and it causes a constant
microfilariemia in the peripheral blood of the host.
To consider the possibility of escape of larvae from the proboscis into the
environmental media, the fate of the filarial larvae was studied. They survived
5-24 hours in saline, serum of blood cell solution and were destroyed within one
hour in well or tapwater. The natives believed that filaria could be infected
orally (by drinking well water) but this is not believable from the evidence above.
The present study supplements the knowledge of bionomics of microfilariae and
infective filarial larvae of the Brugia malayi and Dirofilaria immitis. The results
are summarized as follows:
(1) Fourteen species of mosquitoes were collected in the endemic areas of
filariasis, including Yongju, Chinju, and Cheju-Do.
(2) Culex pipiens and Anopheles sinensis were predominant in inland Korea, and
Aedes togoi and Aedes albopictus in Cheju-Do(island).
(3) Microfilaria immeitis developed to infective stage in Culex pipiens from 16
days, in Aedes albopictus from 13 days and in Aedes koreicus from 14 days.
The rate of development of microfilariae to the infective stage in the mosquitoes
was 68.5 per cent in Culex pipens, 20.3 per cent in Aedes albopicuts and 45.0
percent in Aedes Koreicus.
(4) The infective larvae which escaped from the proboscis of the mosquitoes
survived one hour in water and 40 hours in human and dog serum.
(5) The transfused microfilaria immitis survived as long as as 105 days in
healthy dog vessels.
(6) The peak density of microfilariae in the peripheral blood of the host
appeared at 23-24 o'clock in B.malayi and at 00-01 o'clock in D.immitis.
(7) Microfilaria immitis showed negative heliotropism.
(8) Diethylcarbamazine citrate administration appeared to cause no definite
effect on microfilaria in ;the peripheral blood of the malayian filariasis cases.
(9) side action including high fever after Diethylcarbamazine citrate treatment
appeared to be due to production of the pyrogenic substance from dead microfilaria
which had been destroyed by the drug.