MVSc

In the recent years, frequent outbreaks of poultry
diseases have caused significant economic losses and among the
various sources of infection, freeflying migratory birds and
waterfowls are reported to be an important source for the
introduction of disease to domestic flocks. These freeflying
pirds and waterfowls abound in the waterlogged areas of Kerala
especially Alleppey, Kottayam, Thrissur and Malappuram
districts. Heavy losses were reported each year due to severe
outbreaks of duck plague and duck pasturellosis resulting in
the wiping out of the duck population in the state. This may
be due to the introduction of the disease agents by migratory
waterfowls. Hence a study was undertaken to elucidate the
role of waterfowls in the spread of diseases to domestic
poultry and ducks.
A total of 52 waterfowls were caught from different parts
of Kerala of which 15 were lesser whistling teals and 37 were
gargany. Postmortem examination of these birds were carried
out and the required materials were collected. Impression
smears from the cut surface of the liver revealed intranuclear
inclusion bodies in the hepatic cells in four cases (Bird Nos.
17, 23, 27 and 49) and two haemagglutinating agents were
isolated from the cloacal swabs of the bird numbers 18 and 22.

The haemagglutinating agents developed lesions in the
chicken embryos which died 3 to 5 days after inoculation. the
allantoamniotic fluid of the affected embryos agglutinated
teal and chicken erythrocytes. The lesions exhibited by the
embryos infected with Ta were congestion of the CAM and
embryos while in T22 the embryos were stunted, curled and at



the same time congested.


The liver of the embryo had



yellowish brown patches. The haemagglutination activity of
both the viral isolates were tested with red cells of various
species like cattle, horse, human '0', duck, rabbit and pig
but was negative in all cases.



Both the isolates lost their infectivity and haemagglutination property at 56°C for 30 min. the infectivity
and HA activity of the viral isolates T18 and T22 were retained
at pH 7.2 and were completely destroyed at pH 3.2 and pH 9.
Both the isolates were sensitive to treatment with chloroform,
revealing both as enveloped viruses, wherein the infectivity
was completely lost and HA activity was considerably reduced.
In the case of Tl8 HA activity was reduced from 512 to 16 and
for T22 from 128 to 8. The nucleic acid types of the viral
isolates were confirmed by inoculating the isolates to chicken
embryo fibroblast cultures pretreated with 100 µg and 200 µg
per ml of IudR which led to the conclusion that Ta was a RNA


virus and T22 a DNA virus.


The ELD50 of Ta and T22 were 107



ELD50/ml and 106 ELD50/ml. The ICPI, MDT and IVPI. were
calculated as for NDV. The ICPI for the isolates were 0.83

and 0.30 for T18 and T22 respectively, MDT was 120 hr for both
and the IVPI was calculated to be zero in both cases,
indicating that both the isolates were nonpathogenic.
In cell cultures both the isolates produced CPE which
affected the whole monolayer by 96 hrs. In the case of Tl8 the
CPE was characterised by rounding and clumping of cells, the
infected cells showing a tendency to get separated from the
neighbouring cells leaving long cytoplasmic strands, syncytium
formation with four or five nuclei and severe cytoplasmic
vacuolation. For T22 the CPE was characterised by rounding and
cytoplasmic vacuolation and karryorhexis. Intranuclear and
intracytoplasmic inclusion bodies could be demonstrated.
The pathogenicity studies of both the isolates were
carried out in one week old and six week old ducklings and
chicken, for which both were nonpathogenic and did not exhibit
any clinical signs or mortality. But viral infection was
established in six week old chicks by virus isolation till the
14th day of infection from the cloacal swabs for both the
isolates. The sera collected from these birds revealed an
antibody titre of 16 for T¬18 and 8 for T22 indicating the
infection. The antigenic relationship of the isolates was
examined with NDV, EDS-76 and fish viruses (FV and F6), of
which T22 did not show any antigenic similarity with any of the
viruses. But T1B on the contrary exhibited antigenic
relationship with the fishviruses FV and F6 but no antigenic





similarity with NDV and EDS-76. The antigenic similarity
exhibited by T18 with the fish viruses leads to the conclusion
that waterfowls may be disseminating the viruses responsible
for the outbreak of epizootic ulcerative syndrome in fishes.
The morphological features of T18 by electronmicroscopy

revealed an enveloped virus with a size of 150-185 nm with
pleomorphic forms and peplomers of a length of 18-20 nm.
Except the length of the peplomers it similated a
paramyxovirus. The morphology of T22 was not studied due to
technical defects.