zDALY: An adjusted indicator to estimate the burden of zoonotic diseases

Abstract

The burden of human diseases in populations, or for an individual, is frequently estimated in terms of one of a number of Health Adjusted Life Years (HALYs). The Disability Adjusted Life Year (DALY) is a widely accepted HALY metric and is used by the World Health Organization and the Global Burden of Disease studies. Many human diseases are of animal origin and often cause ill health and production losses in domestic animals. The economic losses due to disease in animals are usually estimated in monetary terms. The monetary impact on animal health is not compatible with HALY approaches used to measure the impact on human health. To estimate the societal burden of zoonotic diseases that have substantial human and animal disease burden we propose methodology which can be accommodated within the DALY framework. Monetary losses due to the animal disease component of a zoonotic disease can be converted to an equivalent metric using a local gross national income per capita deflator. This essentially gives animal production losses a time trade-off for human life years. This is the time required to earn the income needed to replace that financial loss. This can then be assigned a DALY equivalent, termed animal loss equivalents (ALE), and added to the DALY associated with human ill health to give a modified DALY. This is referred to as the “zDALY”. ALEs could also be estimated using willingness-to-pay for animal health or survey tools to estimate the replacement time value for animals with high societal or emotional value (for example pets) that cannot be calculated directly using monetary worth. Thus the zDALY estimates the impact of a zoonotic disease to animal and human health. The losses due to the animal disease component of the modified DALY are straightforward to calculate. A number of worked examples such as echinococcosis, brucellosis, Q fever and cysticercosis from a diverse spectrum of countries with different levels of economic development illustrate the use of the zDALY indicator.

Improved methods to capture the total societal benefits of zoonotic disease control: Demonstrating the cost-effectiveness of an integrated control programme for Taenia solium, soil transmitted helminths and classical swine fever in northern Lao PDR

“…Although methods to estimate the costs of zoonotic disease to both livestock productivity and humans have been proposed [ 68 – 69 ], there has been no totally satisfactory conceptual framework for analyzing the total societal burden of zoonotic disease; that is the combined costs of disease from both the humans and animals [ 70 ]. The recently developed concept of the zDALY addresses this gap [ 65 ]. This study had both zoonotic ( T .…”

“…The zoonotic DALY (zDALY) was also used as an alternative approach to estimate the cost-effectiveness ratio of controlling T . solium taeniasis/cysticercosis [ 64 – 65 ]. Just like the aggregate net cost method, the zDALY also provides a framework for combining the human burden and the losses incurred by livestock keepers in single metric and it does this by considering the monetary impact on livestock keepers in terms of a time trade-off, in the sense of the value of people’s time required to recoup these losses, and by using gross domestic product (GDP) as a numéraire, it convert these into a non-monetary time unit called ‘animal loss equivalent’ (ALE) [ 65 ].…”

Modelling for Taenia solium control strategies beyond 2020

“…• true prevalence of T. solium infection in humans and pigs because of poor diagnostic methods • adult tapeworm life span • effect of pig-to-people population ratio on transmission • processes regulating parasite acquisition in humans and pigs 26 • health and economic burden 2,3 and cost-effectiveness of interventions (DALYs likely to underestimate disease burden); possible use of the zoonotic zDALY metric 21 • linking infection to disease models, particularly to human neurocysticercosis and epilepsy 27 What are the biggest risks?…”

“…1), which will help refine modelling simulations. Integrating dynamic transmission models with burden of zoonotic disease 21 and economic frameworks will help quantify the human health and agricultural sector gains and the cost-effectiveness of achieving newly defined global targets for zoonotic neglected tropical diseases. In northern Lao People's Democratic Republic, the cost-effectiveness of different intervention options was assessed.…”

A planetary vision for one health

“… 33 Employing a comprehensive One Health framework encourages multidisciplinarity in global health research, education, programme and policy assessments, planning, and implementation. It also requires further development of useful metrics for tracking One Health outcomes, 36 as well as better ways to assess impact. 31 …”