![]() 70 million people live in at risk areas covering over one and a half million square kilometres. Human African trypanosomiasis (HAT), more colloquially known as sleeping sickness, is a deadly disease which is endemic across much of sub-Saharan Africa. To be completed by Erin Human African Trypanosomiasis (HAT) This work considers the effects of using "host-only" transmission models such as the quasi-equilibrium assumption upon disease dynamics and also the effect of omitting the latency period upon epidemic predictions. Some of Kat’s work focuses on the simplifications that are often made to reduce the complexity of models. Even when only considering just one specific disease the variations in the disease within different populations may lead to changes in not just the parameterisation, but also of how one may wish to take the modelling approach. Unsurprisingly models from the literature range greatly from deterministic to stochastic, endemic (including birth and death rates) or epidemic (an outbreak of limited duration), incorporating spatial spread, spatial heterogeneity, latency periods, age structure, acquisition and loss of immunity, multiple strains and many others. There are many different types of mathematical model for vector-borne disease transmission ideally these are sought to be kept mathematically tractable and as simple as possible whilst retaining the general dynamics of the biological system. Modelling the Dynamics of Vector-Borne Diseases Typically mathematical models of vector-borne diseases are based upon a two-population SI(R) model exhibiting “criss-cross” infection terms, where and are the force of infection of terms for hosts and vectors respectively:ĭependent upon the disease and population being modelled, this may be adapted to incorporate other more specific features. a feeding rate or vector desire to bite.abundance and spatial spread of both hosts and vectors.When the parasite has reached a certain stage in its reproductive cycle, the host becomes infectious after which, if it is bitten, it can transmit the disease to a susceptible vector through its parasite-infected blood and completing the transmission cycle (shown in the figure below).ĭisease transmission is usually characterised by: The time after becoming infected but before becoming infectious is known as the latency period. At this stage, if infected, the host is considered exposed but suers no adverse eects from the infection and cannot transmit the disease. ![]() Once bitten, the host has a chance to become infected with the disease. The typical course of infection for vector-borne transmission, ignoring disease, host or vector specics, starts with an infected vector (a blood feeding or sucking adult arthropod) taking a blood-meal from a susceptible member of the host population. Human diseases are not the only concern there are many others that infect other classes of hosts which are also of interest, particularly from the point of view of preserving endangered species. Such diseases are rife in the developing world a combination of optimal habitat for vectors in tropical regions and a lack of medical aid lead to large-scale endemics there. The story is similar for leishmaniasis where there are around 12 million people globally who are thought to be infected at any given time and about 80,000 people die annually from the most serious form, visceral leishmaniasis. ![]() Malaria, leishmaniasis, dengue fever and west Nile virus are but to name a few which currently have a huge social impact on human populations.Įach year in the region of 225 million people are infected with the malaria parasite and in 2009 around 781,000 of these resulted in disease-induced mortality. There are many such diseases, the dynamics of which are of great interest from the point of view of controlling infection. Vectors are usually haematophagous (blood-feeding) arthropods such as mosquitoes, sandflies or ticks. A vector-borne disease (specifically a biological transfer rather than mechanical) is one in which transmission of infection in a population (the host population) occurs only via a second population (vectors).
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