The study was undertaken in eight endemic districts of Orissa, India, to find the members of the species complexes
of Anopheles culicifacies
and Anopheles fluviatilis
distribution patterns. The study area included six forested districts (Keonjhar, Angul, Dhenkanal, Ganjam, Nayagarh and Khurda) and two non-forested coastal districts
(Puri and Jagatsingpur) studied over a period of two years (June 2007-May 2009). An. culicifacies
A, B, C and D and
S and T sibling species were reported. The prevalence of An. culicifacies
A ranged from 4.2-8.41%, B
from 54.96-76.92%, C from 23.08-33.62% and D from 1.85-5.94% (D was reported for the first time in Orissa, except
for occurrences in the Khurda and Nayagarh districts). The anthropophilic indices (AI) were 3.2-4.8%, 0.5-1.7%, 0.7-
1.37% and 0.91-1.35% for A, B, C and D, respectively, whereas the sporozoite rates (SR) were 0.49-0.54%, 0%, 0.28-
0.37% and 0.41-0.46% for A, B, C and D, respectively. An. fluviatilis
showed a similarly varied distribution pattern in
which S was predominant (84.3% overall); its AI and SR values ranged from 60.7-90.4% and 1.2-2.32%, respectively.
The study observed that the co-existence of potential vector sibling species of An. culicifacies
(A, C and D) and An.
S (> 50%) was responsible for the high endemicity of malaria in forested districts such as Dhenkanal,
Keonjhar, Angul, Ganjam, Nayagarh and Khurda (> 5% slide positivity rate). Thus, the epidemiological scenario for
malaria is dependent on the distribution of the vector sibling species and their vectorial capacity.