| dc.description.abstract | Newcastle disease is an infectious and highly
contagious disease affecting mainly chickens and turkeys.
Various other birds as well as in may be affected
by the virus. In recent years, the disease has caused
severe economic losses in Kenya. Outbreaks of the
disease have occurred even in areas where, in the past,
vaccination had been practiced regularly. Though
much work has been done in other countries, very little
work has been carried out in Kenya regarding the
biological and biophysical nature of the virus .and
also the disease. It was therefore necessary to
study the occurrence of the disease in Kenya and the
behaviour of some associated locally isolated virus
strains.
Data on the outbreaks of the disease and on
positive diagnoses was collected from the annual
reports of the Kenya Veterinary Department with the
kind permission of Dr. Chema, Deputy Director of
Livestock Development (Research), and used to study
the epidemiology and ecology 0 the disease. Thirty two
virus isolates were recovered from clinical
materials submitted for laboratory diagnosis from
different parts of Kenya. Their biophysical and
biological characteristics were determined, namely:-
(xiii)
1. 'l'he ability of the virus to haemagglutinate
fowl, equine, bovine, ovine, caprine and
canine erythrocytes.
2. Inactivation of the haemar;agglutination activity
and infectivity by heat, ultraviolet light
and disinfectants.
3. Serological relationships by cross
haemaggIu'ti.na.Lton-d.nhLb.i, tion tests.
4~ Residual and eluted virus using 2 strains
at room temperature.
5. Times to elution at 400.
6. Heplication and cytopathogenicity of the
virus in various cell cultures.
'7I
• Viability of the virus in various ma t er-i.a'l s
at room temperature (water, feed , litter J soiI
and feo.thers )•
. The disease was found to be widely distributed
throughout the country. Analysis of positive diagnoses
of the disease for the period 1967 - 1980 showed a
trend with three peaks in a year coinciding with the
cold and we t periods in the year. The highest peak
occurred in the June July period. The trend of
positive diagnoses and number of outbreaks declined
progressively with the use of the killed vaccine that
was first used in 1958 -- 1959. By 1965, the Leve I
(xiv)
of the disease had reached a low value after vhich
there was a dramatic rise. The level of the disease
declinBd again in 1972 - 1973 with the introduction
of the F strain vaccine.
All the isolates haemagglutinated fowl, bovine,
ovine and canine erythrocytes. Most of them
haemagglutinated caprine erythrocyte"'. Five isolates
haemaggutilna t.8:u1 equl.ne ery t_hrocy tes au-!- both 4°C
37°C, 10 haemagglutinated the same cells at 37°C
and
and
not at 4°C while 17 isolates failed to haemagglutinate
them at all. Twenty isolates had heat stable
haemagglutinins anc1 12 had heat labile haemagglutinins.
Some strains were heat labile for haemaggl1.l.tination
activity and infectivit.y wh i.Le others »iex:e stable in
both parameters. Ultraviolet light treatDent increased
the titre fourfold within 4 hours of exposure for some
isolate s wh i Le for others the titre remained unchanged.
Thirteen isolates were classified as fast elutors and
19 as slow eLut ors, Graphic(~l presentation of residual
and eluted virus against 'ti.me showed characteristic
hyperbolic curves. Cross haemagglutination-inhibition
tests among 6 isolates and 2 vaccine strains and
their antisera sh9wed high titTes for each virus and
its homologous antiserum but highly var-Lab Le reactions
with heterologous antisera.
All isolates tested produced cytopathic effects
in cells of chicken embryo, sheep lung, sheep kidney
and calf kidney cells characterised by rounding up of
cells and complete degeneration within 96 hours.
Eosinophilic cytoplasmic inclusion bodies were also
observed. Syncytia formation was observed only in
cells of the chicken embryo. The virus multiplied
to higher titres in chicken embryo lung cells,
chicken embryo intestinal cells and chicken embryo
heart cells than in chicken embryo fibroblastso
The virus was destroyed in 10 minutes by 1%
and 0.1% lysol, 1% sodium hypochlorite, 70% ethyl
alcohol and 1:400, 1:600, 1:2000 and 1:6000 dilutions
of biocid-30. The virus could not.be destroyed
completely by 4% formalin in 10 minutes.
The virus survived for 7 days in water and
feathers, 10 days in soil and 14 days in mash and
litter at room temperature. The virus survived for
21 days in water containing 2% (w/v) bovine serum
albumin (BSA), 28 days in water containing 10% BSA·
and 49 days in water containing 20% BSA.
These findings indicate clearly that there
are marked variations among the Newcastle disease
virus isolates present in Kenya. This may explain
some of the field observations related to the
Newcastle disease. | en |
