Abstract
Environmental temperature is a key driver of malaria transmission
dynamics. Using detailed temperature records from four sites
(1800-3200m) in the western Himalaya, we model how temperature regulates
parasite development rate (the inverse of the extrinsic incubation
period, EIP) in the wild. Using a Briére parametrization of the EIP,
combined with Bayesian parameter inference, we study the thermal limits
of transmission for avian (P. relictum) and human Plasmodium
parasites (P. vivax and P. falciparum) as well as for two
malaria-like avian parasites, Haemoproteus and Leucocytozoon. We
demonstrate that temperature conditions can substantially alter the
incubation period of parasites at high elevation sites (2600-3200m)
leading to restricted parasite development or long transmission windows.
We then compare estimates of EIP based on measures of mean temperature
versus hourly temperatures to show that EIP days vary in cold versus
warm environments. We found that human Plasmodium parasites
experience a limited transmission window at 2600m. In contrast, for
avian Plasmodium transmission was not possible between September
to March at 2600m. In addition, temperature conditions suitable for both
Haemoproteus and Leucocytozoon transmission were obtained
from June to August and in April, at 2600m. Finally, we use temperature
projections from a suite of climate models to predict that by 2040, high
elevation sites (~ 2600 m) will have a temperature range
conducive for malaria transmission, albeit with a limited transmission
window. Our study highlights the importance of accounting for fine-scale
thermal effects in the expansion of the range of the malaria parasite
with global climate change.