Natural vertical transmission of dengue viruses by Aedes aegypti in Chennai, Tamil Nadu, India.
OBJECTIVE
Dengue viruses are spread and maintained in an Aedes aegypti-human- Ae. aegypti cycle in urban areas of the tropics. Dengue viruses are also maintained in nature by vertical transmission by Ae. aegypti. A study was undertaken in Chennai, a known endemic city in south India, to comprehend the natural vertical transmission dynamics in Ae. aegypti and to assess its epidemiological importance.


METHODS
Ae. aegypti males collected in resting and landing collections were tested for dengue virus infection by antigen-capture enzyme-linked immunosorbent assay (ELISA) and further examined by insect bioassay, Toxorhynchites splendens inoculation-indirect immunofluorescence technique (Toxo-IFA) using serotype-specific monoclonal antibodies (Mabs), if found positive by ELISA.


RESULTS
Of the 509 pools of Ae. aegypti males (n=5408) screened, 15 pools, collected in April, June- July, November-December in 2003 and March, May in 2004, were found positive for dengue virus infection and the minimum infection rate (MIR) among adult males was high in June 2003 (28.0/ 1000). Three positive pools could be serotyped as dengue-2 (2 pools) and dengue-3 (1 pool).


CONCLUSIONS
Dengue virus isolations from wild caught males of Ae. aegypti indicate the occurrence of transovarial transmission. Vertical transmission was mainly observed in summer months when dengue infections in humans were low suggesting that dengue viruses adopt a novel strategy of surviving adverse climatic conditions.
Arunachalam
N
N
Centre for Research in Medical Entomology ICMR, Madurai, India. crmeicmr@icmr.org.in
Tewari
S C
SC
Thenmozhi
V
V
Rajendran
R
R
Paramasivan
R
R
Manavalan
R
R
Ayanar
K
K
Tyagi
B K
BK
D000330:Aedes / Q000821:virology*; D000818:Animals; D003715:Dengue / Q000453:epidemiology* / Q000635:transmission*; D003716:Dengue Virus / Q000302:isolation & purification*; D019353:Endemic Diseases; D006801:Humans; D007194:India / Q000453:epidemiology; D018445:Infectious Disease Transmission, Vertical; D008297:Male; D012621:Seasons