Abstract
Peste des petits ruminants (PPR) is an acute viral disease of small ruminants that inflicts
severe economic losses of livestock of Bangladesh every year. This study focused on the
prevalence and epidemiology of PPR in Bangladesh, pathology of PPR on natural
infections, quick diagnostic method for PPR, and isolation of PPR virus (PPRV) from
different outbreaks and their molecular characterization. Epidemiological data, serum and
tissue samples from PPR suspected outbreaks and pathological information at necropsy
were collected and analyzed. Formalin fixed tissues were processed for histopathological
and immunohistochemical study. RT-PCR was adapted with primer sets for different
genes and compared for their sensitivity and specificity. In addition, blood and nasal
swabs were collected on filter paper from PPR suspected live animals at febrile and nonfebrile stages for molecular detection and genotyping of PPRV. Possibility of storing
samples on filter paper under various conditions, deep-frozen or at ambient temperature
was explored for exchange between laboratories or for archiving viral RNA. F gene of a
representative local isolate was cloned and sequenced. RT-PCR positive PPR samples
were subjected to PPRV isolation and propagation in Vero cells. Twenty eight (28)
outbreaks were investigated where the overall morbidity and mortality were 74.92% (63%
to 100%) and 58.71% (23%-100%), respectively. Mortality was higher in the young goat
(<1 year). Introduction of newly purchased animals from the market played important role
in transmission of the virus in the flock. Movement of goats during religious festivals
increased PPRV spread in goats. An overall sero-prevalence was 21% indicating majority
of goats were not protected against PPRV. At necropsy, emaciated and dehydrated
carcasses, severe hemorrhagic enteritis, consolidated lungs and hemorrhagic lymphnodes
were observed. Microscopically, enteritis with large mononuclear cell infiltration,
tracheitis, broncho-interstitial pneumonia with large mononuclear cell infiltration and
fibrin accumulation were found. PPRV antigen was detected immunohistochemically in
the bronchial epithelial cell and macrophages in the lung alveoli. Seven PPRV isolates
were obtained and all the isolates produced cytopathic effects at 48-72 hrs post inoculation
on 3rd passage. Primers specific for N genes were found more sensitive than other genes in
detecting PPRV from field samples. With the samples collected on filter paper, RT-PCR
amplifying a 448-bp fragment of the F gene appeared positive for both blood and nasal
swabs when animal were in febrile state and only nasal swab yielded positive detection
when samples were taken in non-febrile state. PPR viral RNA could still be detected from
filter paper after 10 months storage at –70°C, demonstrating the excellent capacity of filter
papers to store genetic material. Phylogenetic analysis of sequence data F and N gene
fragments revealed that Bangladeshi PPRV belongs to Lineage IV. The F gene sequences
were relatively more conserved. The sequence divergence within Lineage IV ranged from
0.3% to 3.2% only and that between the lineages ranged from 6.3% to 13.6%. The N gene
sequences were more variable; the sequence divergence within Lineage IV ranged from
0.8% to 9.0% and that between the lineages ranged from 9.0% to 23.8%. Amino acid
substitutions in the F protein were scattered, whereas, a huge number of amino acid
substitutions were noted in the N protein. The N protein of recent Lineage IV isolates has
two unique amino acid substitutions which are not evident in other Lineage IV isolates.
The findings of the present study would enrich understanding regarding the status and
epidemiology of PPR in Bangladesh. It also enables to understand the molecular
characteristics of PPRV in Bangladesh. Filter paper method of sample collection provides
a simple and powerful approach for large-scale screening and epidemiological studies.
Analysis of partial sequence of F and N genes also demonstrate that the PPRV strain from
Bangladesh is genetically quite similar with the PPR viruses currently circulating in
southern Asia and are apparently developing into a new sub lineage within Lineage IV.