Citation
Abd Rahman, Sohayati
(2009)
Epidemiology, Transmission And Isolation Of Nipah Virus In Large Fruit Bats (Pteropus Species)In Peninsular Malaysia.
PhD thesis, Universiti Putra Malaysia.
Abstract
Bats of the genus Pteropus are considered the natural reservoir hosts for NiV and other
henipaviruses. The present study was carried out to investigate the epidemiology of NiV
in Pteropus sp. in Malaysia. The specific objectives of this study are to describe the
geographical distribution and population characteristics of Pteropus spp. in the
peninsular, describe the geographical extent of NiV antibody in pteropid bats in the
peninsular, identify the risk factors associated with the infection, determine the natural
route of NiV excretion, transmission and serological patterns of the infection in captured
Pteropus, estimate the seroprevalence and incidence rate of NiV seroconversion in the
bats and investigate the possibility of viral recrudescence in naturally infected bats and in
experimentally NiV immuno-suppressed seropositive bats P. vampyrus and P. hypomelanus were found throughout Peninsular Malaysia.
P. hypomelanus inhabits the islands surrounding the peninsular while P. vampyrus were
found on the mainland. P. vampyrus was extremely sensitive even to low-level human
activities. Physically, P. vampyrus was significantly bigger and heavier than P.
hypomelanus. The physical characteristics of bats of both species differ significantly
given age and sex. Both species had similar breeding pattern throughout the year.
The seroprevalence of NiV in P. hypomelanus and P. vampyrus were 11% and 32.5%,
respectively. The odds ratio of seropositive for NiV was higher in P. vampyrus compared
to P. hypomelanus. A repeated cross-sectional study show that NiV seroprevalence in a
single population of P. hypomelanus ranged between 1% and 20%. The seroprevalence
was found associated with time and the reproductive status of female bats. The bats that
were either pregnant, lactating, carrying or nursing a pup were at a significantly higher
risk to be seropositive when compared to dry bats.
A prospective study on the bats revealed at least 5 basic serological patterns: i) High
Static Positive, ii) Low Static Positive, iii) Waned-off, iv) Waned-off and Rising and v)
Static Negative. Passive immunity to NiV of pup born to seropositive dam was detected
for a period of up to a year. This suggests that the maternal antibody against NiV may last
up to a year in captive bats.
The isolation of the virus from a bat’s urine from ‘Waned-off and Rising’ antibody
pattern provides for the first time, the objective evidence of the possible viral
recrudescent in Pteropus bats. The virus was excreted in very low concentration and in a very short time period. This indicates that a very narrow window exist where NiV is shed
by bats in the wild. The seroconvertion of another two bats within a month after the virus
isolation suggests the possibility of horizontal transmission within the colony. The NiV
incidence rate for seroconversion was 486 per 1000 bat-year.
Stress in seropositive bats induced chemically resulted in an increased neutrophil and
decrease in lymphocytes count. However, no virus was discovered from samples
collected during the experiment and from organs at the end of the study.
The findings from the study have contributed significantly to the understanding on the
distribution of NiV among healthy Pteropus bats, transmission and persistency of the
virus within the colony, and the basic bat immune response due to NiV infection
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