Title page for ETD etd-10252010-161938

Document Type Master's Dissertation
Author Cramer, Tamlyn Jill
Email s21075931@tuks.co.za
URN etd-10252010-161938
Document Title Monitoring the African horsesickness virus life cycle by real-time RT-PCR of viral dsRNA
Degree MSc
Department Genetics
Advisor Name Title
Prof H Huismans Co-Supervisor
Dr V van Staden Supervisor
  • CPE
  • Equidae family
  • cellular pathogenesis effects
  • African horsesickness virus
  • AHSV
Date 2010-09-02
Availability unrestricted

African horsesickness (AHS), caused by African horsesickness virus (AHSV), is an infectious, non-contagious, insect-borne viral disease that affects members of the Equidae family. AHSV is a non-enveloped virus, consisting of 10 segments of double stranded RNA (dsRNA) encoding seven structural and four non-structural proteins. Infection of mammalian cell cultures with AHSV leads to severe cellular pathogenesis effects (CPE), whereas insect cells show no noticeable CPE. Differences are also apparent between different serotypes of AHSV with regards to viral production, viral release, membrane permeabilisation and CPE. In this study we investigated different aspects of the AHSV life cycle in cell culture.

The first aim of this study was the development of a real-time RT-PCR assay to quantify and monitor dsRNA from AHSV-infected cells. The dsRNA was used to quantify viral production, as dsRNA (one copy of each segment) is found only within viral particles and is not free within the cytoplasm of infected cells, thus giving a true representation of the amount of virus. This was achieved by cloning genome segment 5, optimising the extraction and purification of dsRNA, optimising the cDNA synthesis reaction, as well as the establishment and standardisation of the real-time PCR reaction.

The second part of the study investigated and compared viral production and viral release between three different serotypes of AHSV in either mammalian or insect cell lines. The amount of dsRNA, which represented cell associated virus from AHSV-3- and AHSV-4-infected BHK cells over a 48 hr time period, was monitored by real-time RT-PCR and revealed a second wave of dsRNA production. These findings possibly suggest that a second round of infection of released viruses is re-entering previously uninfected or infected cells to replicate further. AHSV production was monitored in KC cells and indicated no production of progeny virions. However, an improvement was obtained when AHSV was first passaged on KC cells before being used for infections. The results from this study are in agreement with the fact that for a particular virus to replicate efficiently in a specific cell line, it should first be adapted to those cells.

The dsRNA was quantified from samples representing equivalent amounts of infectious virus (i.e. same titre values) of AHSV serotypes 2, 3 or 4. The amount of dsRNA was approximately four-fold higher from serotype 2 than from serotypes 3 and 4. When the percentage of viral entry into cells was analysed, the majority (approximately 90%) of virus from serotypes 3 and 4 entered the cells, whereas serotype 2 showed viral entry of only about 50%. These findings suggested that a large amount of virus from serotype 2 was non-infectious, while the majority of virus from serotypes 3 and 4 was infectious. However, serotype 2 was a great deal more cytotoxic to cells (e.g. earlier onset and severity of CPE) when compared to cells infected with either serotypes 3 or 4.

2010, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Cramer, TJ 2010, Monitoring the African horsesickness virus life cycle by real-time RT-PCR of viral dsRNA, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-10252010-161938/ >


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