Abstract:
Flying foxes (Pteropid bats) are known for disease transmission of viral diseases to other
animals and to humans for decades. One suspected factor for the viral shedding in bats is
physiological stress. Although flying fox colonies are found island wide, no study has been
carried out to assess and interpret the stress hormone levels of bats in Sri Lanka.
Glucocorticoids (cortisol and corticosterone) are known stress hormones which change in terms
of physiological stress. Therefore, we assessed physiological stress levels of tested flying foxes
using urinary cortisol measurements. Urine was collected non-invasively from two different
roosts in two climatic zones; Viharamaha Devi Park Colombo – wet zone (6°54'44.4"N
79°51'45.0"E) (n=432) and Thaleimannar – arid zone (9°05'31.5"N 79°43'38.5"E) (n= 402) in
Sri Lanka for a 6-month period from November 2018 – April 2019. Collected samples were
inactivated using a standard inactivation protocol (RKI in-house SOP) under BSL 3 laboratory
conditions at the RKI, before assessing cortisol levels. Urine creatinine was measured, and
these creatinine values were used to normalize the cortisol concentration. Cortisol
concentration ranged between 10.90 – 2912.17 ng/ml with average of 195.15 ng/ml in
Thaleimannar roosting site and ranged between 4.89 – 2451.74 ng/ml with average of 173.85
ng/ml in Colombo roosting site. Overall urinary cortisol concentration of Pteropus giganteus
ranges from 4.89 – 2912.17 ng/ml in Sri Lanka with average of 199.68 ng/ml. Results showed
that cortisol concentration in urine tend to vary each month in both locations. This could be
due to the environmental factors such as temperature, rainfall, and availability of food in the
particular time period. It could also be due to physiological changes caused by mating and
pregnancy. With these initial data, the study is continuing to include intermediate and dry
climatic zones to get a clear understanding of the fluctuations of physiological stress in flying
foxes in Sri Lanka.
