Background
Health economists have traditionally quantified the burden of vector-borne diseases (such as chikungunya and dengue) as the sum of the cost of illness and the cost of intervention programmes. The objective of this paper is to predict the order of magnitude of possible reduction in tourism revenues if a major epidemic of chikungunya or dengue were to discourage visits by international tourists, and to prove that even a conservative estimate can be comparable to or even greater than the cost of illness and intervention programmes combined, and therefore should not be ignored in the estimation of the overall burden.

Methods
We have chosen three Asian economies where the immediate costs of these diseases have been recently calculated: Gujarat (an economically important state of India), Malaysia, and Thailand. Only international tourists from non-endemic countries have been considered to be discouraged, and a 4% annual decline in their numbers has been assumed. Revenues from these tourists have been calculated assuming that tourists from non-endemic countries would spend, on average, the same amount as all international tourists. These assumptions are conservative and consistent with the recent experience of Mauritius and Réunion islands. Non-Resident Indians (NRIs) have been considered half as likely to avoid travel to Gujarat compared to non-Indians. This paper reports inflation-adjusted expenditure figures as 2008 US$, assuming recent market exchange rates of 42.0 INR/US$, 3.22 MYR/US$, 0.68 EUR/US$, and 33.6 THB/US$.

Findings
A 4% decline in tourists from non-endemic countries would result in a substantial loss of tourism revenues . at least US$ 8 million for Gujarat, US$ 65 million for Malaysia, and US$ 363 million for Thailand. The estimated immediate annual cost of chikungunya and dengue to these economies is US$ 90 million, US$ 133 million, and approximately US$ 127 million respectively, indicating that impact on tourism revenues should not be ignored when calculating the burden of infectious diseases. The impact on Gujarat is relatively less because its share of world tourism receipts is just 0.04%, whereas Malaysia and Thailand have healthy shares of 1.64% and 1.82% respectively. A 4% decline in tourists to Gujarat from other Indian states would amount to US$ 9.6 million loss in domestic tourism revenues to Gujarat.

Interpretation
This paper shows that potential loss of tourism revenues due to a severe epidemic outbreak could be substantial. In some cases, ignoring this component could seriously underestimate cost-benefit results, forestalling promising interventions that could benefit the society as a whole or leading to inadequate investment of resources in prevention and public-funded control programmes. This would be to the detriment of especially poorer sections of the society, who may not be able to afford treatment costs. At present data are insufficient for us to make more than a preliminary estimate of the magnitude of the potential loss of revenues from tourism due to a major outbreak of chikungunya or dengue.