Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: HIV infection is one of the world’s biggest health problems, with millions of
people infected worldwide. HIV infects cells in the immune system, where it
primarily targets CD4+ T helper cells and without treatment, the disease leads
to the collapse of the host immune system and ultimately death. Mathematical
models have been used extensively to study the epidemiology of HIV/AIDS.
They have proven to be effective tools in studying the transmission dynamics of
HIV. These models provide predictions that can help better our understanding
of the epidemiological patterns of HIV, especially the mechanism associated
with the spread of the disease.
In this thesis we made a functional comparison between existing epidemiological
models for HIV, with the focus of the comparison on the force of infection
(FOI). The spread of infection is a crucial part of any infectious disease, as
the dynamics of the disease depends greatly on the rate of transmission from
an infectious individual to a susceptible individual.
First, a review was done to see what deterministic epidemiological models
exist. We found that many manuscripts do not provide the necessary information
to recreate the authors’ results and only a small amount of the models
could be simulated. The reason for this is mainly due to a lack of information
or due to mistakes in the article.
The models were divided into four categories for the analysis. On the basis of
the FOI, we distinguished between frequency- or density-dependent transmission,
and as a second criterion we distinguished models on the sexual activity
of the AIDS group. Subsequently, the models were compared in terms of their
FOI, within and between these classes. We showed that for larger populations,
frequency-dependent transmission should be used. This is the case for HIV,
where the disease is mainly spread through sexual contact.
Inclusion of AIDS patients in the group of infectious individuals is important
for the accuracy of transmission dynamics. More than half of the studies
that were selected in the review assumed that AIDS patients are too sick to
engage in risky sexual behaviour. We see that including AIDS patients in the
infectious individuals class has a significant effect on the FOI when the value
for the probability of transmission for an individual with AIDS is bigger than
that of the other classes.
The analysis shows that the FOI can vary depending on the parameter values
and the assumptions made. Many models compress various parameter values
into one, most often the transmission probability. Not showing the parameter
values separately makes it difficult to understand how the FOI works, since
there are unknown factors that have an influence. Improving the accuracy
of the FOI can help us to better understand what factors influence it, and
also produce more realistic results. Writing the probability of transmission
as a function of the viral load can help to make the FOI more accurate and
also help in the understanding of the effects that viral dynamics have on the
population transmission dynamics. / AFRIKAANSE OPSOMMING: MIV-infeksie is een van die wêreld se grootste gesondheidsprobleme, met miljoene
mense wat wêreldwyd geïnfekteer is. MIV infekteer selle in die immuunstelsel,
waar dit hoofsaaklik CD4+ T-helperselle teiken. Sonder behandeling lei die
siekte tot die ineenstorting van die gasheer se immuunstelsel en uiteindelik sy
dood. Wiskundige modelle word breedvoerig gebruik om die epidemiologie van
MIV/vigs te bestudeer. Die modelle is doeltreffende instrumente in die studie
van die oordrag-dinamika van MIV. Hulle lewer voorspellings wat kan help
om ons begrip van epidemiologiese patrone van MIV, veral die meganisme wat
verband hou met die verspreiding van die siekte, te verbeter.
In hierdie tesis het ons ‘n funksionele vergelyking tussen bestaande epidemiologiese
modelle vir MIV gedoen, met die fokus van die vergelyking op die
tempo van infeksie (TVI). Die verspreiding van infeksie is ‘n belangrike deel
van enige aansteeklike siekte, aangesien die dinamika van die siekte grootliks
afhang van die tempo van oordrag van ‘n aansteeklike persoon na ‘n vatbare
persoon.
‘n Oorsig is gedoen om te sien watter kompartementele epidemiologiese modelle
alreeds bestaan. Ons het gevind dat baie van die manuskripte nie die nodige
inligting voorsien wat nodig is om die resultate van die skrywers te repliseer
nie, en slegs ‘n klein hoeveelheid van die modelle kon gesimuleer word. Die
rede hiervoor is hoofsaaklik as gevolg van ‘n gebrek aan inligting of van foute
in die artikel.
Die modelle is in vier kategorieë vir die analise verdeel. Op grond van die
TVI het ons tussen frekwensie- of digtheidsafhanklike oordrag onderskei, en
as ‘n tweede kriterium het ons die modelle op die seksuele aktiwiteit van die
vigs-groep onderskei. Daarna is die modelle binne en tussen die klasse vergelyk
in terme van hul TVIs. Daar is gewys dat frekwensie-afhanklike oordrag
gebruik moet word vir groter bevolkings. Dit is die geval van MIV, waar die
siekte hoofsaaklik versprei word deur seksuele kontak.
Die insluiting van die vigs-pasiënte in die groep van aansteeklike individue
is belangrik vir die akkuraatheid van die oordrag-dinamika van MIV. Meer
as helfte van die uitgesoekte studies aanvaar dat vigs-pasiënte te siek is om
betrokke te raak by riskante seksuele gedrag. Ons sien dat die insluiting van
vigs-pasiënte in die groep van aansteeklike individue ‘n beduidende uitwerking
op die TVI het wanneer die waarde van die waarskynlikheid van oordrag van
‘n individu met vigs groter is as dié van die ander klasse.
Die analise toon dat die TVI kan wissel afhangende van die parameter waardes
en die aannames wat gemaak is. Baie modelle voeg verskeie parameter waardes
bymekaar vir die waarskynlikheid van oordrag. Wanneer die parameter waardes
nie apart gewys word nie, is dit moeilik om die werking van die TVI te verstaan,
want daar is onbekende faktore wat ‘n invloed op die TVI het. Die
verbetering van die akkuraatheid van die TVI kan ons help om die faktore
wat dit beïnvloed beter te verstaan, en dit kan ook help om meer realistiese
resultate te produseer. Om die waarskynlikheid van oordrag as ‘n funksie van
die viruslading te skryf kan help om die TVI meer akkuraat te maak en dit kan
ook help om die effek wat virale dinamika op die bevolkingsoordrag-dinamika
het, beter te verstaan.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96983 |
| Date | 04 1900 |
| Creators | De la Harpe, Alana |
| Contributors | Snoep, J. L., Stellenbosch University. Faculty of Science. Dept. of Biochemistry. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xv, 110 pages : colour illustrations |
| Rights | Stellenbosch University |
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