Evidence brief: The economic burden of loiasis: A comprehensive cost-of-illness analysis of regionally representative, individual-level data from rural Gabon

Abstract

Loiasis is a vector-borne filarial infection endemic to parts of sub-Saharan Africa. It disproportionally affects economically disadvantaged communities in rural, forested regions. To better understand the economic burden of loiasis, we conducted a comprehensive cost-of-illness study in an endemic region of Gabon, with the aim of quantifying the financial costs incurred by individuals infected with the disease from a societal perspective. We conducted a cross-sectional survey in 2023 in rural Gabon. Study participants took part in diagnostic testing for loiasis and were interviewed based on a standardized questionnaire covering a wide range of medical and non-medical costs. Participants reporting eye worm migration or harboring loiasis microfilariae were defined as loiasis positive. Various cost estimates were derived by creating a synthetic control group by means of entropy-balancing and then applying generalized linear models (GLM) for the study region. We show that the average annual costs directly attributable to loiasis amount to 39.94 USD per individual per year. Average cost estimates are primarily driven by indirect costs and direct non-medical costs. We further show that in the rarer cases that individuals seek treatment at formal or informal healthcare providers for loiasis-specific symptoms, costs from the patient’s perspective can be excessively high and amount to about 43 percent of the average monthly per capita income in the study region.

1. Introduction

Loiasis, a parasitic infection transmitted by deerflies, is estimated to affect more than 20 million individuals in the rural parts of West and Central Africa [1,2]. Initially considered a benign condition whose main policy relevance lay in complicating treatment for onchocerciasis (river blindness) and lymphatic filariasis in cases of co-infection [3,4], loiasis has received limited attention. However, recent studies demonstrate that the infection can have severe health consequences, including a substantial burden of disease [4], impaired cognition [5], organ failure [6], and even excess mortality [7,8].

The high number of infected individuals in Africa, combined with growing evidence of the adverse health effects of loiasis, has led many scholars to call for its inclusion on the WHO’s list of neglected tropical diseases (NTDs) [1,8–10]. This demand is further reinforced by recent epidemiological data showing the infection’s increasing presence and repeatedly documented negative consequences.

Few studies have yet attempted to estimate the economic burden of loiasis and shed light on the direct and indirect costs attributable to the disease. While several studies report that loiasis patients suffering from acute symptoms (e.g., migration of the adult worm through the conjunctiva of the eye, Calabar swelling or headaches [11,12]) seek treatment from health professionals including nurses, doctors, and traditional healers [13,14], cost estimates are not readily available. Some preliminary evidence on costs is provided by Veletzky and colleagues. Focusing exclusively on loiasis-positive individuals in an endemic region of rural Gabon and obtaining item-specific price data from small sub-samples, the authors simulate loiasis-specific treatment costs under various scenarios. According to the authors’ preferred specification, loiasis resulted in treatment costs of 58 United States Dollars (USD) per person per year [14].