Some Models for Epidemics of Vector-Transmitted Diseases

TL;DR

This paper develops and analyzes two epidemic models for vector-borne diseases like dengue, chikungunya, and Zika, incorporating direct transmission for Zika, and applies the models to real outbreak data to estimate key epidemiological parameters.

Contribution

It introduces a novel epidemic model that includes both vector transmission and direct sexual transmission for Zika virus, with methods to estimate the basic reproduction number from data.

Findings

Derived expressions for basic reproduction number in both models

Showed how to estimate R0 from initial exponential growth rate

Fitted model parameters to Zika outbreak data in Colombia

Abstract

Vector-transmitted diseases such as dengue fever and chikungunya have been spreading rapidly in many parts of the world. The Zika virus has been known since 1947 and invaded South America in 2013. It can be transmitted not only by (mosquito) vectors but also directly through sexual contact. Zika has developed into a serious global health problem because, while most cases are asymptomatic or very light, babies born to Zika - infected mothers may develop microcephaly and other very serious birth defects. We formulate and analyze two epidemic models for vector-transmitted diseases, one appropriate for dengue and chikungunya fever outbreaks and one that includes direct transmission appropriate for Zika virus outbreaks. This is especially important because the Zika virus is the first example of a disease that can be spread both indirectly through a vector and directly (through sexual contact). In both cases, we obtain expressions for the basic reproduction number and show how to use the initial exponential growth rate to estimate the basic reproduction number. However, for the model that includes direct transmission some additional data would be needed to identify the fraction of cases transmitted directly. Data for the 2015 Zika virus outbreak in Barranquilla, Colombia has been used to fit parameters to the model developed here and to estimate the basic reproduction number.