Effects of environmental temperature on parasite development
(Extrinsic Incubation Period)
Using the thermodynamic parasite development model, we estimated the
effect of using the mean daily temperature and mean hourly temperature
on the calculation of the EIP for each site (1800-3200m). Our methods
described the rate of parasite development for Plasmodium species
(two human and one avian Plasmodium ), Haemoproteus , andLeucocytozoon parasites (Figure 3) at varying temperatures. For
high elevation sites (3200m), the EIP estimates for all parasites using
both measures suggested that transmission was not possible throughout
the year. Below, we describe where results from both measures coincide,
for other elevations and parasites, as well as where they differ in
detail. We find that both measures, based on either the diurnal
temperature range or the mean temperature, very largely give similar
results for the periods of the year where the EIP is within the
allowable range for transmission. However, for specific months, it is
possible that transmission is possible within one scheme but not within
the other (Figure 4).
For the 2600m site, there was no parasite transmission predicted using
the EIP based on both temperature measures for P. falciparum andP. vivax from May to March. However, in June, the mean
temperature range predicted no transmission of P. vivax whereas
the EIP days of 46.9±15.71 using the diurnal temperature range. In
April, the EIP days for P. vivax were longer by 13.95 days using
the diurnal temperature range (EIP days: 36.08±3.5) than the mean
temperature (EIP days: 22.13±4.04). The EIP days for P.
falciparum were 5.62 days shorter using mean temperature measures (EIP
days:40.29± 12.11) than the diurnal temperature (EIP days: 45.91±10.64)
in April.
For avian Plasmodium relictum , using both mean temperature and
diurnal temperature range, September to March was predicted as no
transmission period and May to August and April as predicted
transmission, at 2600m. In April, the EIP was 18.7 days longer using the
diurnal temperature range (EIP days:32.95±16.29) than the mean
temperature range (EIP days:14.25±2.25). For two malaria-like avian
parasites, Haemoproteus and Leucocytozoon , September to
March were predicted as no transmission period and June to August was
predicted as the transmission period (< 1 day difference in
EIP estimates) using both temperature measures. However, diurnal
temperature range predicted no parasite transmission in April whereas
mean temperature range estimated the EIP days of 8.27±1.1 and 5.62±0.75,
for Haemoproteus and Leucocytozoon , respectively.
For the 2000m site (Anusuya), October to March was predicted to have no
transmission period for P. falciparum and P. vivax using
both temperature measures. In April, using the mean temperature
predicted EIP days of 37.12±27.34 for P. falciparum and
34.73±9.66 for P. vivax , however no transmission was obtained
using the diurnal temperature range. Using the mean temperature, there
was no P. falciparum transmission predicted for May and
September. However, the diurnal temperature range approach predicted EIP
days of 51.7±17.94 in May and 50.7±17.02 in September.
Among avian parasites, P. relictum transmission window was
predicted from May to September using both temperature measures.
However, there was no P. relictum transmission predicted in
October using mean temperatures while the diurnal temperature range
method estimated EIP days of (47.4±19.46). In March, use of the diurnal
temperature range predicted no P. relictum transmission whereas
the mean temperature range measure suggested EIP days of 46.03±17.43. In
April, both temperature measures predicted P. relictumtransmission, however, EIP days using diurnal temperature range were
3.06 longer than for the mean temperature. For two malaria-like
parasites, Haemoproteus and Leucocytozoon, transmission
was predicted from June to September using both temperature measures.
There was no Haemoproteus transmission predicted for October to
April using both temperature measures. In May, Haemoproteusshowed no transmission using mean temperature whereas, using the diurnal
temperature, transmission was predicted with showed EIP days of
15.44±8.54. However, Leucocytozoon transmission was not predicted
from November to February, while only the mean temperature supported EIP
days of 17.71±13.56 in March and April. The diurnal temperature range
method indicated transmission in October with EIP days of 19.81±7.8.
For the lowest elevation site (1800m), P. falciparum and P.
vivax showed no transmission from December to February using both
measures, the DTR and the mean temperature. An exception was for P.vivax where the use of the diurnal temperature range showed an
EIP of 51.6±10.72 days in the month of February. The effect of
daily temperature variations on P. falciparum and P. vivaxpredicted a transmission window from May to October, March, and April.
In November, there was no transmission using the mean temperature for
both P. falciparum and P. vivax. The use of the diurnal
temperature range predicted transmission for both parasites in that
month, with EIP more than 45 days in both cases.
In contrast, for P. relictum , use of the diurnal temperature
range suggested transmission throughout the year. However, the use of
the mean temperature showed no transmission across the months December
to February. For the two malaria-like parasites, transmission months
ranged from May to October for Haemoproteus and May to November,
as well as April, for Leucocytozoon. The exceptions were: using
the mean temperature led to transmission in March while using the
diurnal temperature range led to transmission in April forHaemoproteus . In March, there was no transmission predicted using
the diurnal temperature range while mean temperature range predicted EIP
days of 12.79±11.96 for Leucocytozoon .
Our comparisons of mean temperature collected using experimental logger
data and WorldClim data from 2014-2015 showed threshold temperature not
supporting parasite transmission at the high elevation site (3200m)
throughout the year (Suppl. Fig. S1). However, at the 2600 m site,P. vivax transmission was predicted from May to September and
April whereas experimental data suggested only in April. For avian
parasites, P. relictum , Haemoproteus andLeucocytozoon the window in which transmission is predicted is
largely similar using these two source datasets, albeit leading to
longer EIP days with experimental data, with the only exception for the
month of April where this systematics are reversed. This larger pattern
was reversed at 1800 m, with shorter EIP days with experimental data as
compared to using WorldClim data, with the only exception again being
for the month of April. The 2000m site showed closely similar
transmission patterns for all parasites using both datasets, again
except for the months of March and April, for P. relictum andLeucocytozoon .