A Comparative Assessment of Epidemiologically Different Cutaneous Leishmaniasis Outbreaks in Madrid, Spain and Tolima, Colombia: An Estimation of the Reproduction Number via a Mathematical Model

Abstract

Leishmaniasis is a neglected tropical disease caused by the Leishmania parasite and transmitted by the Phlebotominae subfamily of sandflies, which infects humans and other mammals. Clinical manifestations of the disease include cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis (MCL) and visceral leishmaniasis (VL) with a majority (more than three-quarters) of worldwide cases being CL. There are a number of risk factors for CL, such as the presence of multiple reservoirs, the movement of individuals, inequality, and social determinants of health. However, studies related to the role of these factors in the dynamics of CL have been limited. In this work, we (i) develop and analyze a vector-borne epidemic model to study the dynamics of CL in two ecologically distinct CL-affected regions—Madrid, Spain and Tolima, Colombia; (ii) derived three different methods for the estimation of model parameters by reducing the dimension of the systems; (iii) estimated reproduction numbers for the 2010 outbreak in Madrid and the 2016 outbreak in Tolima; and (iv) compared the transmission potential of the two economically-different regions and provided different epidemiological metrics that can be derived (and used for evaluating an outbreak), once R0 is known and additional data are available. On average, Spain has reported only a few hundred CL cases annually, but in the course of the outbreak during 2009–2012, a much higher number of cases than expected were reported and that too in the single city of Madrid. Cases in humans were accompanied by sharp increase in infections among domestic dogs, the natural reservoir of CL. On the other hand, CL has reemerged in Colombia primarily during the last decade, because of the frequent movement of military personnel to domestic regions from forested areas, where they have increased exposure to vectors. In 2016, Tolima saw an unexpectedly high number of cases leading to two successive outbreaks. On comparing, we estimated reproduction number of the Madrid outbreak to be 3.1 (with range of 2.8–3.9), which was much higher than reproduction number estimates of the Tolima first outbreak 1.2 (with range of 1.1–1.3), and the estimate for the second outbreak in Tolima of 1.019 (with range of 1.018–1.021). This suggests that the epidemic outbreak in Madrid was much more severe than the Tolima outbreak, even though Madrid was economically better-off compared to Tolima. It indicates a potential relationship between urban development and increasing health disparities.

Autochthonous Outbreak of Cutaneous Leishmaniasis due to Leishmania infantum in Corrientes Province, Argentina

“…That said, the molecular biology studies that have taken place in northwestern Argentina (in Salta) and in the province of Santiago del Estero have not identified this species. 3,7,8 Our analysis suggests an urbanization of CL, which is consistent with similar clinical and epidemiological patterns observed in the Mediterranean basin, 30,31 and the presence of good transmission vectors and high prevalence of canine infection, which facilitate the spread of the disease. 28,29 These circumstances could herald a much greater impact and magnitude of CL in the region in the near-to-medium term.…”

Data scarcity and ecological complexity: the cutaneous leishmaniasis dynamics in Ecuador

“…Using data from Valle Hermoso, we estimated R 0 to be around 3.9, suggesting potential for regular outbreaks in future and need for significant improvements in existing intervention programmes. Our estimate of R 0 is higher than estimate reported from neighbouring countries Colombia (R 0 = 1.3 [48]) and Peru (R 0 = 1.9, if domestic dogs are primary reservoirs [66]), which could be due to a difference in the reporting system and/or ecology of the subregions. Nevertheless, the results suggest that improved reporting and early treatment of cases can control the disease drastically; however, the rates of decrease in cases will depend on intensity to control alternative host ( potentially bird) density in the region.…”

“…A compartmental type epidemiological framework was proposed to model anthropozoonotic parasite transmission in a community of two hosts (birds as potential host and humans as an alternative host) and a vector species (similar models are developed and analysed in [30,34,47,48]). The model includes an additional compartment that corresponds to the unreported cases, considering that in rural areas there is no access to conventional treatment, and lacks traditional and ancestral knowledge of the disease [15,32,49].…”

Estimating the basic reproduction number for the 2015 bubonic plague outbreak in Nyimba district of Eastern Zambia

“…As the infection was assumed to be spread through vectors, the Ross Macdonald Susceptible-Infectious-Removed-Susceptible-Infectious model, denoted as SIR-SI, was initially created as a first step in the modelling process [ 38 ]. This model type, originally developed for malaria, is a standard mathematical model for vector-borne pathogens that tracks the infections in both the human and the vector populations [ 6 , 25 – 27 , 36 , 37 , 38 , 44 – 46 ]. The parameter values used for creating the model were obtained from various literature and where such information could not be readily found the parameter values were estimated based on reasonable assumption and biological plausibility.…”