S.pullorum infection in layers and layer parents
SUMMARY
This case involved the occurrence of clinical disease, drop in
egg production, though little mortality in parent birds of
layer chickens. Mortality in young chicks was not reported to
be associated with this occurrence. A case with similar
bacteriological results in a layer flock derived from the
breeder farm is also described.
2.1. Parent Flock.
PRESENTING PROBLEM
Drop in egg production and some sick birds in a flock in lay.
HISTORY
Year:1986 Country: Brazil Case: 86-050
Bird Species: Chicken Bird Type : Layer Parent
Breed: <DELETED> 130-PS Age: 302 days
Symptoms: A few sick birds were noticed in the flock.
Yellowish diarrhoea was also noticed. An egg production drop
of about 20% over the week prior to presentation was
experienced. The farm manager stated that egg production drops
had occurred in previous flocks and that they tended to
persist to the end of the production cycle.
Birds on farm: 40.000
Birds in flock: 2.500
Birds affected: 200
Total Mortality: Not available
Mortality last 3 days: 2-3 per week
Age when problem first noted: 295 days
Feed type: Mash feed mixed on site
Water source: Artesian well
Water treatment: None
Litter type: Shavings, good condition
Vaccination History:
Marek Day 1 at hatchery
Newcastle Salisbury, days 7 (eye drop),30,60,120 (drinking
water),180 (Oil emulsion)
EDS-76 Salsbury, day 100 (Injectable)
Bronchitis Salisbury, days 3,30,60,120(water), 180 (Oil
emulsion).
Treatment already performed : None
CLINICAL AND PATHOLOGICAL INVESTIGATION
Clinical examination:
A total of six birds were presented for examination. All were
alive on arrival at the laboratory and exhibited the clinical
signs described above by the farm manager.
Post-mortem examination:
Similar lesions were found in all birds although there was
considerable variation in their extent. There was
hepatomegaly associated with foci of necrosis and petechial
haemorrhage in the liver tissue. The spleens were also
increased in size and in some of the birds
there was peri-splenic peritonitis. There was also
degeneration of ovules with a tendency towards desiccation and
the formation of caseous contents.
Presumptive Diagnosis :
Bacterial septicemia, probably Fowl typhoid. The low
mortality reported was the major factor which did not fit with
Fowl Typhoid.
Immediate action :
Firm instructions were given to the farm manager to place the
flock and its egg production in strict isolation pending the
results of laboratory examinations.
Laboratory examinations:
Material from the ovary, liver and spleen were plated directly
on Blood Agar, Brilliant Green Agar (BGA) and were also
incubated in Selenite Broth. A rich growth of small
transparent colonies were obtained on the primary BGA cultures
in less than 24 hours. The reaction in the medium was typical
of Salmonella (colour change from yellow to red). The
bacterial growth was submitted to direct agglutination testing
using Difco somatic antigen polyvalent sera and was found to
be group D. A simple biochemical series was set up using
Triple Sugar Iron Agar (TSI), maltose broth and dulcitol
broths. These were read in less than 48 hours after the
original accession (24 hours after inoculation). The reactions
were :
TSI : Acid (yellow) butt, alkaline (red) slant, no H2S
(black) at 24 hours although there was some on re-examination
at 48 hours after inoculation.
Maltose : Acid but no gas.
Dulcitol: Neither acid nor gas.
These reactions are typical of Salmonella pullorum
At this point the diagnosis was changed to Pullorum Disease
although because of the atypical presentation and severe
visceral lesions there was a lingering doubt about Fowl
Typhoid. Reference cultures of the isolate were prepared and
aliquots were submitted to the national Salmonella reference
centre, the Oswaldo Cruz Foundation, Rio de Janeiro. The
results were as follows :
Glucose : Acid without gas
Dulcitol : Neither acid nor gas
H2S : Negative at 1 day
Serology : Somatic group D1 (antigens 9,12)
The identification given was Salmonella pullorum, thus
confirming the diagnosis of Pullorum Disease.
Outcome :
The following advice was given to the veterinarian responsible
for the farm:
"Although it is theoretically possible to eliminate S.pullorum
from a flock through repeated blood testing and elimination of
reacting birds, this is unlikely to prove successful or
worthwhile in the present case because of the following
factors :
1. The flock is close to the end of production.
2. The seriousness of the lesions suggest that within-flock
transmission would be unusually high.
3. The number of birds clinically affected and the magnitude
in the drop in egg production suggest that a significant
proportion of the flock are already infected.
Based on the above considerations the following specific
recommendations are made:
a. The affected flock and any eggs in the hatchery should be
eliminated.
b. An intensive program of cleansing and disinfection of all
materials which have been in contact with the infected flock,
eggs or recently hatched chicks.
c. The house-cleaning program should begin by damping down the
litter with water containing iodophor or creoline. It should
be removed in covered trucks. The house and all equipment
should then be thoroughly washed down with water and then
disinfected by a 5% Formol spray with the curtains up
(respirator needed for operator). The house should be left
closed for at least one week, then disinfected with a
quaternary-ammonium product and allowed to dry. The
surrounding area should be cleaned up and sprayed with the
same QAC.
d. Repeat pullorum testing (100% rapid whole-blood
agglutination) on all flocks in production. Submit reactors
to bacteriological testing.
e. Avoid continuous prophylactic use of furazolidone, and do
not administer any antibiotics in the 3-4 weeks prior to
pullorum testing.
f. Investigate any further cases of clinical disease, drops in
egg production or chick mortality.
g. Generally tighten up on 'bio-security'. Entry into poultry
houses to be strictly on basis of need. Verify control of
vehicles, materials and personnel. Educate site personnel
about potentially disastrous consequences of the spread of
this disease in a parent operation."
Over the following four months this and a number of other
flocks were eliminated and the whole system of preventative
medicine was tightened up. The control of the disease was
facilitated by the fact that the houses were well separated on
the site (minimum distance between nuclei of 100 meters) and
by the relatively warm and dry climate in the area. This
resulted in the elimination of S.pullorum infection, however
there is no doubt that infected chicks must have been produced
over an extended period (mainly prior to the diagnosis being
established).
Discussion :
This case has a number of interesting features. We normally
expect that a chicken-specific Salmonella causing clinical
disease in adult birds will be S.gallinarum. Obviously some
strains of S.pullorum are relatively pathogenic for adult
birds even though they may not cause quite as serious diseases
as S.gallinarum. The fact that mortality of chicks produced
by the affected flock was not reported is worth noting. There
are a number of possible explanations:
1. The mortality was occurring but was not reported to the
diagnostician.
2. The infection was so recent that infected chicks had not
begun to hatch.
3. The bacterial strain was so virulent that infected embryos
did not develop, pip, or hatch.
4. Routine antibiotic therapy was being used during the first
few days of life.
I would consider that the last option is the most likely.
Gentamycin is also often included in the Marek's disease
vaccine for chicks from problem flocks.
The occurrence of such a dramatic example of a disease which
is rarely seen in modern poultry production raises the
question "What went wrong ?". There were a number of
contributing factors. The poultry health scheme operated by
the state government in the 60's and 70's probably would have
prevented this occurrence. In fact a new nation-wide scheme
was put into operation by the Ministry of Agriculture.
However this scheme is largely bureaucratic in nature,
authorising or not the functioning of new breeder farms
according to the submitted plans of houses and hatcheries.
Few Ministry inspectors visit the field, fewer still are
experienced in poultry production. Although the
private/company veterinarian responsible for each breeder farm
is supposed to file results of pullorum testing and disease
diagnosis, compliance with the regulations is probably less
than 100%. Although the files of the diagnostic laboratories
are generally available to the Ministry this information is
not usually sought out. There is a general feeling that when
problems do occur the voluntary action of the industry will be
more effective and technically correct than that imposed by
the Ministry. Independent testing of the antigens in use is
lacking. Positive and negative test sera to help train
technicians are difficult to come by. A new voluntary
certification plan is now under development which is hoped to
remedy some of these deficiencies.
2.2 Layers
HISTORY
Year:1988 Country: Brazil Case:88-005
Bird Species: Chicken Bird Type :Layer
Breed: <DELETED> Age: 300 days
Clinical Signs: Drop in production, 20-30% in 2 of 3 nuclei.
Slight reduction in feed consumption. Considerable increase
in soft-shelled eggs.
Birds on farm: 120.000
Birds in flock: 10.000
Birds affected: ??
Total Mortality: Normal
Mortality last 3 days: None
Age when problem first noted: About 2 weeks prior
Feed type: Mash mixed on farm. No
recent changes of formula or
raw-materials.
Water source: Artesian well
Water treatment: No chlorine
Litter type: None - conventional cages
Vaccination History:
Marek Day 1 at hatchery.
Newcastle Salsbury, days 5 (eye drop),30,60,120 (drinking
water).
Bronchitis Salsbury, days 5,30,120(water).
Treatment already performed : Weekly insecticide sprays for
preceding four weeks, Carbaryl 85% 40 kg/1000 litres +
Dichlorvos 1 litre/1000litres. Spray was applied with a
tractor-mounted spray for agricultural use.
CLINICAL AND PATHOLOGICAL INVESTIGATION
Clinical examination:
Seven live and superficially normal hens were presented. Comb
size and leg pigment were variable but not markedly reduced.
Moderate to heavy infestation with the tropical dermanyssid
mite Ornithonyssus bursa was evident.
Post-mortem examination :
There was plenty of oystershell visible in the food material
present in the gizzard. A few tapeworms (Raillietina sp.)
were found in the small intestine. Abnormally formed ovules
were noted in the ovaries of four birds. Localised
peri-ovarian peritonitis was also noted in these same birds.
Other organs were unremarkable.
Presumptive diagnosis:
The moderate to severe infestation with blood-sucking mites
was considered to be the most severe problem afflicting the
submitted birds. Contamination of feed and water with
insecticides could have contributed to the drop in production.
The recent high ambient temperatures in these
non-environmentally-controlled houses could also have
contributed.
Immediate action:
Treatment of birds with a pyrethroid compound using small
power or hand sprayers, preferably with the feeders and
drinkers empty. In any case, care should be taken in not
contaminating feed or water. Consider use of concentrated
pyrethroid solution in PVC tubes threaded along the back of
the cages.
Laboratory tests :
Serological tests (Haemagglutination -Inhibition, HI) were
negative for Egg Drop Syndrome (<1:16) and low positives for
Infectious Bronchitis and Newcastle disease (to be expected in
vaccinated birds). Bacterial culture of the deformed ovules
revealed a rich growth of Salmonella pullorum by direct
plating on Blood Agar and BGA. Identification of the bacterium
was by the same techniques and with the same results described
above in the case in parent birds.
Outcome :
Effective treatment of the ectoparasite problem resulted in a
general improvement in the health of the flock and a gradual
return to the normal egg production curve. Some birds which
were obviously not in lay were culled.
Discussion :
In contrast to the previous case, here there were no
extra-ovarian visceral lesions attributable to S.pullorum.
The finding of these carrier birds is probably incidental to
the actual occurrence of the drop in egg production (although
it is interesting that the problem occurred at the same stage
of lay as in the parent bird case reported above). The high
incidence of pullorum-carriers in the present sample may be
simply due to the flock manager selecting those birds which
were a bit off-colour for laboratory examination. Note that he
did not describe the occurrence of sick birds in the flock and
considered mortality to be below normal. The provisional
diagnosis quoted above was probably correct.
It is tempting to suggest that this flock was congenitally
infected with pullorum disease. It was supplied by the same
organisation as that which managed the parent operation
described above. However both flocks could have become
independently infected from the reservoir of infection which
is known to occur in back-yard flocks. This would be
particularly easy for a layer flock because the general level
of bio-security is much lower than that observed for breeder
flocks.
The presence of S.pullorum did not necessitate specific
control measures in this flock because:
1. S.pullorum has not been reported to cause human disease so
table egg contamination was not a problem.
2. The flock was close to the end of the production cycle.
3. The fact that the birds were caged in small groups limited
the spread of the disease, whether by faecal contact or by
consumption of infected eggs (the shell-less eggs could have
been a problem if the birds had been on deep litter).
4. Not being parent birds, no vertical transmission will
occur.
5. The infection was not associated with noticeable clinical
illness in a significant number of birds.
6. Anti-bacterial therapy would have led to residues in the
eggs.
A number of non-specific measures applicable to the control of
any infectious disease were instituted:
A. Movement of personnel between infected and non-infected
sites was prohibited.
B. Proper disposal of carcasses using a pit with vermin-proof
lid was instituted.
C. Insecticidal spraying of dung was to be used if fly numbers
increased.
====================================================================
Paul Mc Mullin MVB CertPMP MRCVS
MSD AGvet
Hertford Road
Hoddesdon
Herts
Current (10/98) Contact Details:
E-mail:PaulMcMullin@Compuserve.com
Note for Certificate Candidates:
This copy of the case-histories were prepared for the RCVS library after
the examination. The author is identified. Materials to be presented for
examination should however, be anonymous.
Acknowledgments should be provided separately
(see examination regulations for further details).