Return to search

Diversity and evolution of coronaviruses and astroviruses in bat, wildbirds and rodents

Bats and birds are known to be the reservoirs of a number of zoonotic diseases. The

capacity of flight and the diversity of these animals may make them special in maintaining

and disseminating diverse viruses leading to instances of emerging zoonoses. In particular

bats are increasingly recognized to be reservoirs of a wide range of viruses, including Nipah,

Ebola and severe acute respiratory syndrome (SARS) coronaviruses. In most instances these

viruses appear to establish long-term persistence in bats.

In this thesis I report the identification of novel astroviruses from different

insectivorous species of apparently healthy bats sampled in Hong Kong and in 11 provinces

of Mainland China with high positive rates. Astroviruses are important causes of diarrhea in

many animal species, including humans. This study revealed a remarkably high genetic

diversity of bat astroviruses, which form novel distinct phylogenetic groups in the genus

Mamastrovirus. Evidence for varying degrees of host restriction for bats astroviruses has

been found. The finding of diverse astroviruses in Miniopterus bats captured within a single

cave habitat in Hong Kong illustrates a very unusual virus host relationship between

astroviruses and these bats.

Surveillance of astroviruses in rodents, the only mammal with species numbers

surpassing that of bats, has revealed a novel astrovirus in only 1.6 % of the faecal samples of

urban brown rat (Rattus norvegicus) in Hong Kong in marked contrast with the prevalence

and diversity of astroviruses in bats. Rat astrovirus was phylogenetically related to human

astroviruses MLB1 which was detected from clinical samples from diarrhoeal patients in

Hong Kong in this study. The unusually high positive rates of astroviruses in bats have been

again highlighted.

Avastroviruses were detected in 7.1% of the aquatic wild bird samples. Avastrovirus

have also been detected in doves in Hong Kong, pond herons and a less whistling duck in

Cambodia. A phylogenetic analysis of these novel astroviruses together with other previously

known astroviruses revealed that avastrovirus can be divided into 3 monophyletic groups. On

the other hand, avian coronaviruses was detected in 12.5% of the aquatic wild bird samples.

Phylogenetic analysis of these avian coronaviruses has led us to suggest taxonomic separation

of these viruses into two groups as gammacoronaviruses and deltacoronaviruses. Frequent

interspecies transmissions of gammacoronaviruses between duck species were demonstrated.

Analysis of the avian viral sequences and host mitochondrial DNA sequences suggested that

some coronaviruses may have coevolved with birds from the same order.

With the discoveries of coronaviruses and astroviruses in mammalian and birds, we

now have a better understanding on the diversity and ecology of these two virus families in

wildlife. These findings provide new insights into the ecology and evolution of these viruses

in nature and have revealed possible inter-species transmissions of these viruses. The role of

bats as a reservoir of viruses with potential to pose zoonotic threats to human health was also

reinforced. Studies of the virus ecology in wildlife as demonstrated in this thesis will help

formulating better strategies for controlling emerging diseases in the future. / published_or_final_version / Microbiology / Doctoral / Doctor of Philosophy

  1. 10.5353/th_b4784973
  2. b4784973
Identiferoai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/174531
Date January 2011
CreatorsChu, Ka-wing., 朱嘉永.
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Source SetsHong Kong University Theses
LanguageEnglish
Detected LanguageEnglish
TypePG_Thesis
Sourcehttp://hub.hku.hk/bib/B47849733
RightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License
RelationHKU Theses Online (HKUTO)

Page generated in 0.0021 seconds