Station bulletin

STATION BULLETIN 416

Avian Mass Immunization for

Infectious Bronchitis and

Newcastle Disease

W. R. Dunlop

R. G. Strout

AGRICULTURAL EXPERIMENT STATION

UNIVERSITY OF NEW HAMPSHIRE

DURHAM, N. H.

ACKNOWLEDGMENTS

The authors wish to express their appreciation to Professor
W. C. Skoglund, Head of the Department of Poultry Husbandry
at the University of Xew Hampshire, for his guidance in the re-
search program and the preparation of this liulletin.

We are also grateful to Mr. Robert E. Leventhal, Graduate
Research Assistant in Poultry, and to Mr. Donald E. Coller,
Senior Laboratory Technician, both of the Poultry Department.
University of New Hampshire.

Thanks also are extendetl to the many poultrymen in New
Hampshire who cooperated in this study. The Poultry Disease
Research Committee of the New Hampshire Poultry Growers
Association was instrumental in organizing the poultrymen. With-
out their financial help and willingness to provide experimental
flocks this study would not have been possil)le.

Acknowledgement is also made to the Lederle Laboratories
Division of the American Cyanamid Co. for providing a research
grant to make part of this study possible.

In addition, thanks are also extended to the following poultry
students at the University who did the actual spra}'ing in the field :
Edwin Antz, Harold Albin, Charles Avery, Andrew Brochu, John
Dodge, Fred Jennings, Roger Laber, Jerald Uuimby, and Dean
Towle.

COVER: One method of mass immunization by spray.

JANUARY 1955

Avian Mass Immunization for Infectious
Bronchitis and Newcastle Disease

By W. R. Du nlop and R. G. Strout=^

Introduction

THE PHENOMENAL growth of the poultry industry in the last
decade, manifested in size of flocks rather than in number of flocks, pre-
sents the need for an entirely new approach to poultry disease control.

Areas of heavy poultry populatidu lend themselves, unfortunately, to
rapid spread of acute diseases. An example of this is readily observed in the
prevalence of respiratory conditions, such as infectious bronchitis and New-
castle disease. The control of the diseases over the entire country presents a
very pressing problem. In spite of the highly specialized technicjues of vac-
cinations carried on today, this problem is increasing in magnitude.

It is apparent that in keeping pace with the industry of today, a method
of mass immunization is needed. The arduous task of vaccinating individual
birds not only presents an expensive labor problem but also invites a factor
known as human error. This factor is considered by some to be largely re-
sponsible for the inadequacy of avian immunization programs.

Mass immunization, whether a dust or a spray, is based on one of the
soundest principles in the study of the spread of virus diseases. Specifically,
it is understood that most virus diseases of the respiratory tract are spread
by means of the virus particles riding on dust particles or moisture droplets
in the air.

Review of Literature

In 1948, Hitchner and Johnson (7) reported the use of the Bj strain of
Newcastle virus in the intranasal vaccination of day-old chicks. While the
duration of immunity was not established, day-old vaccinated chicks were
immune at 4 months of age. It was also demonstrated that the vaccinatio;i
of laying birds did not produce any marked drop in egg production. At-
tempts to immunize baby chicks by atomization of the Bj virus resulted in
a high morbidity and mortality, but there was no evidence of paralytic
symptoms.

Later, Bankowski ( 1 ) concluded from laboratory and field vaccination
trials with an attenuated Newcastle virus that the length of exposure to V:W
air-borne virus and the age of the chickens being vaccinated are important
considerations. The results were of a highly encouraging nature.

* Dr. Dunlop is Research Poultry Pathologist and Mr. Strout is Assista-it
Pathologist, New Hampshire Agricultural Experiment Station.

Hitchner in 1950 (5) ohserved that ])ai"fntal iniunniit\ nuiy he over-
come in day-old chicks, and that imninnit\' from da\-iild vaccination mav he
ohtained even in the face of parental immnnitw

Hitchner and Keising in 1952 (6j, however, demonstrated hy labo-
ratory and field trials that atomization of the H, strain of virns offered a
l)ractical method for vaccinating and revaccinating hirds ^ weeks old or
older. By such administration, successful revaccination was accomplished in
l)roiler flocks 4 weeks old after intranasal vaccination at one day of age. Re-
placement flocks revaccinated at 15 to 20 weeks of age demonstrated a good
antigenic res])onse.

It was noted also hy Hitchner and Keising in this same study that the
Bj strain of virus produced a greater reaction when administered to chicks
as a spray than when administered intranasally. The respiratory reaction
varied from flock to flock with negligi])]e mortality exce])t in those cases
where it appeared that a concurrent infection was |)resent.

Luginhuhl {^>) was one of the first workers to combine the vaccinations
of Newcastle and infectious l)ronchitis at an early age. The administration
of this vaccine involved the intranasal route applied to each bird.

Crawley in 1953 (2) and 1954 (3) has demonstrated that chicks could
])c inoctflated by a spray technique from one da_\" of age up to 20 weeks. It
was observed that the com])ination of infectious bronchitis virus and New-
castle disease virus into one vaccine produced less interference in growth
when the 2 vaccines were applied at the same time than if given separately
In regards to Crawley's work it has been found by many investigators dif-
ficult to duplicate Canadian results under American field conditions.

Candling embryos in preparation for vaeoine prodiu'lion.

4

Experimental Materials

Newcastle Disease Virus

I'he strain oi Xewcastle disease virus used was the Wi or Blacksburg
strain. In the field trials (with one exception, in which a commercial vaccine
was used), the avian embryo titre of this virus was 10 "''-^''. This strain was
obtained directly from llitclmer in 1951.

Infectious Bronchitis Virus

From observations of held outbreaks of infectious l>ronchitis, it was
quite ap])arent that variations in strains occurred.

In 1951, fifteen strains of infectious l)ronchitis were isc^lated, and for
the remainder of that year and up to 'the fall of 1952, repeated screenings
of these strains were carried out. This work resulted in tlie selection of one
strain which appeared to be adaptable to mass imnuuiization procedures.
This strain was found to have high antigenic properties.

Screenings of embryo passages were carried out and it was found that
the twentv-fourth and twenty-fifth embryo passages were desirable for the
field trials. The avian enil)ryo titre was 10 ■'•^. using one tenth ml. of
inocuhun per embryo.

Sprayers

Four different s]M"ayer> were used in the field trials.

1. Binks power spra}er (electric)

2. Aerosol hand sprayer

3. Common hand fly sprayer

4. Z & \\' hand spraxer

The type of sprayer first mentioned was used in tlie application of the
commercially dehydrated Xewcastle vaccine and, later, in the application of
the experimental combination of Newcastle and infectious bronchitis viruses
under the direction of a commercial concern.

The three latter types oi sprayers were used in conjunction with the
experimental vaccine prepared in the University of New Hampshire lab-
oratories.

Diluents

The diluents used in the experiments were modified l)uffered saline
solutions.

Chicks

The chicks u.^ed in the experimental lal)oratory trials were obtained
from the poultry department at the University of New Hampshire.

The chicks used in tlie field trials were provided 1)y cooperating

pouhrynien in the state of Xew llam]xshire.

Experimental Procedures

Field Trial Procedure

Due to the fact that the University of Xew Hami)shire did not have
sufficient facilities for Ivophili/.ation of the viruses involved, the vaccines

used were niaintaiued in a frozen state until time of use. Commercial de-
hydration of similar strains of infectious In-onchitis did not materially afTect
the response to the vaccination. In the maj(jrity of trials the vaccine was
mixed at the farm h}- a representative of the poultr}- department. As the
\'(jlume increased in the state, however, it was necessary in manv instances
to mix the vaccine beforehand. Such vaccine was picked up at the laboratory
by the farmer or field service man. Xo difference in results was noted be-
tween those flocks sprayed by a member of the University or those sprayed
l)y tlu' ])oultrvman himself.

Due to the ease of uKjre complete coverage, the majority of flocks
spray-vaccinated were done so at night when the chicks were bedded down.
Night administration was later observed not to be necessarv providing
complete coverage of the chicks could be accomplished. This factor of suc-
cessful daytime inoculation depended <in the type of brooding facilities
encr)untered.

On those farms utilizing space heaters, the fans were turned off during
administration of the vaccine. The type of brooding equipment used did not
aff'ect the results of the vaccination.

In the case of birds being carried through the growing period to the
laying period, it was found necessary, as with commercial vaccines, to re-
vaccinate. This revaccination was carried out at night when the birds were
bedded down or had gone to roost. Simply spraying the vaccine over the
heads of the birds was all that was necessarv to restimulate immunity which

Drilling and disinfecting the embryos prior to inoculation.

Inoculation of the embryo-* witli virus for vaccine jiroduclion.

lasted through the laying year. Individual handling- of the birds was not
necessary.

Blood samples were taken from the chicks at the time of vaccination.
An attempt was made to procure samples at four-week intervals thereafter.
As the volume increased, however, samples were taken from different flocks
at different ages by random sampling.

Explanation of Serological Tests

The H. I. test emploN'ed in this work has been tised as a method of
determining antigenic response to vaccination with the Vt^ strain of New-
castle virus. This test is of the beta type, described l)y F. S. Markham. It
has been shown by challenge with a known virulent strain of virus that
negative tests are not a reliable indication of susceptibility.

The geometric mean titre is a metlTod used in experimental and field
studies in serology, and is employed wlien it is desired to compare one
group with another. Unlike the average, which may be entirely misleading,
the geometric mean titre has a hxed value.

The serum n.eutrali/.ation test used was a variation of the test described
Ijy f'^abricant (4). A serum dilution of 1 :10 was made and mixed with 10,
100. and 1000 neutralizing doses of eml^rvo-adapted infectious bronchitis
virus. Three embryos per diliuion were used. Results were considered pos-
itive when two out of three emI)ryos in the dilution of 100 or more neutra-
lizing doses lived.

The same test was used in the detection of Newcastle antibodies,
except, of course, an embryo-adapted strain of Newcastle virus was used
as antigen.

In challenging for infectious l)ronchitis, a field strain of bronchitis
\irus was used. This strain underwent a bird titre. It was found that a di-
lution of 10^*^ was the end point of infectivity in susceptible birds. A di-
lution of 10~-\, or 1000 infective doses, was applied. .2 cc. intranasally and
.2 cc. intratracheallv.

[hit challenge for Xeuca.stle inuminit) \va> carried mit 1)_\ injecting"
.5 CO. of 10 nild's (oljtained by l)ird titre ) of the Honey strain of virus in-
tramuscnlarlv. l^iirds showing s\mptoms of paralysis were considered as
dead.

Preliminary Laboratory Results

'liiiKiv CHICKS, parentalh' immune to Newcastle disease, were u>ed in the
first laboratory trial. The chicks were sprayed on the second day. A respir-
atory "take" occurred 5 days later which lasted for an additional 5 days. At
5 weeks, blood samples were taken for an H. I. and S. X. test, and the en-
tire group was challenged with 10 mld's (»f the P)oney challenge strain of
Newcastle virus. Two birds died and one showed paralysis. Seventy and
one-half (70.5) per cent of these birds showed positive Td. I. tnres while
79.3 per cent showed positive neutralization litres.

Diu'ing this same period laboratory trials were being run on the se-
lected strains of infectious bronchitis mentioned previously. .\t this juncture
it was decided to combine Newcastle and infectious bronchitis vaccines. The
Blacksburg strain of Newcastle \irus and selected strains of infectious bron-
chitis were used in these trials.

Four parallel groups of 30 susce])tible 4- week-old chicks were sprayed
with combination Newcastle and infectious bronchitis strains. In addition.
2 groui)s of 30 chicks, 3 and 4 days of age. i)arentally imnnnie to Newcastle
and infectious bronchitis were sprayed.

Recording sterility aiul pott'iu-v,

8

The respiratory take was apparent in the \oiinger chicks on the third
or fourth dav, l)eing quite mild until the fifth day. The 4-week-old birds
showed a take on the second day. The length of respiratory take in all
groups was about 15 days. Xn mortality appeared in the older birds during
this time while one chick was lost in the younger group.

All birds were challenged 4 weeks later. One half were challenged by
the intratracheal route with 1000 infective chick doses of a field strain of in-
fectious bronchitis virus. 'Vhe second half were challenged with the Boney
challenge strain of Newcastle virus as previously described. Two birds died
as a result of the Newcastle challenge and one showed paralysis. Three birds
showed mild respirator)- symptoms for two days when challenged with in-
fectious bronchitis.

Following this trial a further laboratorv test was conducted on some
600 chick divided into 6 pens. The parent stock was vaccinated with a field
strain of infectious bronchitis virus and with wing web vaccine for New-
castle disease just as they came into production. Random blood samples
were taken from all groups of chicks and it was apparent that parental im-
munitv existed for Newcastle disease and infectious bronchitis.

The birds were vaccinated with combination Newcastle and infectious
bronchitis vaccine by the spvay technique. The take was mild on the second
and third days. About the fifth day the take was quite apparent. Respiratory
take had disappeared from all groups by the 17th day.

At 8 weeks random blood samples were drawn for serological test. On
Hemagglutination Inhibition test 63.3 per cent showed positive H. I. titres.
while on serum neutralization test for infectious bronchitis 76.8 per cent
showed positive titres.

At 16 weeks onlv 55.1 per cent showed positive H. I. titres for New-
castle disease; 68.8 per cent were capable of neutralizing better than 100
embryo lethal doses of infectious bronchitis virus.

Experimental Results

Spraying with UNH Newcastle Vaccine

During a three-month period. 25 flocks involving 67.280 birds were
inoculated in the field at 2 to 3 days of age with the Bi strain of Newcastle
virus. The spray technique, utilizing the Z & W type sprayer, as well as
others, was used in the administration of this vaccine. The size of the flocks
ranged from 550 to 10.000 chicks. Brooding systems of all types were en-
countered.

In all cases, respiratory symptoms were observed around the fifth or
sixth day post inoculation. The average length of response was 6.5 days. The
mortality from all causes averaged 1.8 per cent for the first two weeks fol-
lowing vaccination. Blood samples, taken at random, were withdrawn at 4.
8, 12, and 16 weeks, respectively. Geometric mean titres are shown in Table
1. (In the compilation of geometric mean titres for this bulletin, serum
samples in the H. I. test were diluted no higher than 1 :128. This explains
the relatively low figure obtained. It must be remembered here that the geo-
metric mean titre is merely a value obtained for the use of comparison
purposes.)

9

8oo

Figure I

RESULTS OF INFECTIOUS BRONCHITIS
VACCINATION BV SPRAY

(weeks)

C/O

CO

O

CD

Zi
<

I—

z>

LU

UNH SPRAY

PARENTAL IMMUNITY "— ■

PARENTAL

IMMUNITY

WEEKS

9 |0 II IX

CO

O

CD

—I
<

900,

8oc

600

SOO

400

Figure H

RESULTS OF INFECTIOUS

BRONCHITIS VACCINATION
BY SPRAY

UNH SPRAY
PARENTAL IMMUNlTy

3 ■^ S 6 7 6 9 lo II la. i3 14- 15

PARENTAL
IMMUNlTy

REVACCINATIOM

MONTHS

10

Table 1. Results of UNH Newcastle Spray Vaccine

Age 4 weeks 5-8 weeks 9-12 weeks 13-16 weeks

Geometric mean titre ~.7S 6.94 7.11 5.582

Serum neutralization tests indicated that y^KS i)er cent of the samples
neutralized 100 or more neutralizing doses.

Random samples of l)irds. withdrawn at the same time for challenge,
exhibited a resistance of d7 .S per cent, with 98.8 per cent of the susceptible
controls dying.

Spraying of Commercial Newcastle Vaccine

During a period covering approximately 3 months, experiments were
undertaken using the Binks power paint spraver in the administration of a
commercially dehydrated Newcastle vaccine.

Approximately 45.750 birds were sprayed at 2 to 3 days of age with
this equipment. The mortality from all causes for 2 weeks following vac-
cination was 1.7 per cent. The fluration of the respiratory symptoms was an
average of 9 days.

Blood samples, taken at random, were withdrawn at 4. 8. and 12 weeks,
respectively. The geometric mean titres are recorded below.

Table 2. Results of Spraying a Commercial Newcastle Vaccine

Age 4 weeks 8 weeks 12 weeks

Geometric mean titre 5.821 5.743 5.133

Unfortunately, due to the lack of adequate space for challenge, this
process was omitted.

Serum neutralization tests showed that 80.9 per cent of the samples
tested neutralized 100 or more neutralizing doses.

Spraying of Combination Newcastle-
Infectious Bronchitis Vaccine (UNH)

Field trials were carried out utilizing the Bi strain of Newcastle virus
in combination with the strain of infectious bronchitis previously described.

The first spray vaccination utilizing the combination of Newcastle and
I)ronchitis vaccines took place on a farm where 100.000 broilers are raised
every 12 weeks, and 50.000 breeders are kept each year. Newcastle disease
was a very serious problem on this farm, for it had experienced outbreaks
of 31 per cent and 85 per cent losses in the past. Infectious bronchitis and
chronic respiratory diseases were also a definite problem.

Blood samples, taken at random on 2- or 3-day-old chicks, showed a
significant H.I. titre in 88.7 per cent of the samples.

The inoculations took place on either the second or third day of age.
Respiratory symptoms were observed on the second day post inoculation
and lasted approximately 16.5 days.

Random samples taken at intervals of 4 weeks presented the following

geometric mean titres.

11

Table 3. Results of Newcastle Spray at Farm No. 1

Age 4 weeks 8 weeks 12 weeks

Geometric mean litre 1.111 7.464 7.127

At ten weeks of age, two groups of ten Ijirds were withdrawn for chal-
lenge purposes. One group was challenged with 1000 infective doses of a
held strain of infectious bronchitis, employing .2 cc. intratracheally. One
bird showed respiratory symptoms against challenge. In the other group,
wdiich was challenged with the Boney strain of Newcastle virus, two birds
showed paralysis.

The mortality from all causes on the 100.000 liroilers was 2.3 per cent
for three weeks following vaccination.

According to serological test, adequate parental immunity was present
in chicks hatched from the spray-vaccinated parents. These chicks were
spray-vaccinated, showing a geometric mean titre of 16.14 at day-old, with
95.0 per cent of the samples tested for bronchitis antilxxlies. neutralizing
100 or more neutralizing doses of an embryo-adapted bronchitis virus.

During the past two years over 3,000,000 birds have been vaccinated
in the State of New Hampshire, with over 200 individual farms having been
involved. The size of the flocks ranged from 100 to 100,000 chicks.
Brooding systems of various types were used on these farms. Management
conditions of all types were also encountered. The age of the chicks ranged
from 1 to 7 days at the time of vaccination.

The mortality figures on the entire number of birds sprayed averaged
2.4 per cent. This figure includes losses from all causes, not merely losses
resulting from the vaccination alone. At one period during the fall and early
winter of 1953, the average mortality was 3.1 per cent, but a change in the
technique at that time lowered the mortality figures. The figures for the
three months following presented an average mortality from all causes of
1.9 per cent.

The symptoms appeared on an average of three days post inoculation.
Such symptoms were generally mild and, in isolated instances, went un-
noticed. The average length of symptoms was approximately 17 days.

Blood samples, taken at the time of vaccination, and at 4-week intervals
thereafter, exhibited the following geometric mean ])attern. (Samples
labeled as day-old may actually be from 2- to 3-day-old chicks, but in all
instances they are pre-inoculation titres.)

Table 4. Results of Newcastle Spray When in Combination with Infectious

Bronchitis

(Pre-Inoc.)
Age Day-Old Weeks

4 5-8 9-12 13-16 16-19 20-f

Gcometric mean titre 15.32 7.52 6.97 8.82 121 4.34 18.24
Positives 86.8% 76.7% 72.57^ 73.0% 75.67c 70.5% 91.8%

'o

Serum neutralization tests for Newcastle disease antibody, while of
necessity very limited, demonstrated that 76.8 per cent neutralized 100 or
more neutralizing doses of an embr}o adapted Newcastle virus strain at 16
weeks of age.

12

Fi

2£

a*

gu

iqure

m

111

2i

QC

h-

ao

l—

^

le

<:

lij

5:

16

0

14-

a-

f-

1^

LU

2:

0

10

LU

^

RESULTS OF NEWCASTLE VACCINATION

By SPRAY

(months)

UNH SPRAY

PARENTAL IMMUWIT/ — ^
MO REVACCI NATION

MONTHS

O
Ct:

O

Li_)

Figure GZ

! RESULTS OF NEWCASTLE VACCINATION
i BY SPRAY

(weeks)

UNH SPRAY —

COMMERCIAL SPRAY — -
PARENTAL INMUNiry - —

1 a.

PAPENT/M- ■^'

WEEKS

13

The serology on the infectious bronchitis presented the data indicated
in Figures 3 and 4. Individual blood samples were used.

The results on the graphs show that 74.2 per cent of the samples neu-
tralized 100 neutralizing doses or better at day-old: 85.7 per cent at 4
weeks, 84.2 per cent at 5-8 weeks, 89.0 per cent at 9-12 weeks, 73.5 per cent
at 13-16 weeks, 96.6 per cent at 17-20 weeks, and 96.7 per cent at 20 weeks
or more. The reason for the higher percentage of positives at 16 weeks and
beyond is the result of revaccinations carried out from 16 to 20 weeks.

At the time blood samples were withdrawn for serological purposes,
birds were also withdrawn for challenge. The ages of the challenge birds
ranged from 4 to 16 weeks. The results are shown in Table 5.

Table 5. Results of Bronchitis Challenge

Vaccinates
Number Birds Symptoms

Controls
Number Birds

Symptoms

Group
Group
Group

I

II

III

25 0
20 1
25 0

2
2
2

2
2
2

Table 6. Results of Newcastle Challenge

Vaccinates
Number Birds Died

Controls
Number Birds

Died

Group
Group
Group

I

II

III

25 2
20 2
25 3

2

2
2

2
2
2

One hundred thirty-eight chicks, found to be susceptible to Newcastle
disease at 4 weeks of age by random sampling, were spray-vaccinated at
the age of 4 weeks. Two birds died during the period of symptoms. Twelve
random samples taken at 6 weeks of age exhibited a geometric mean titre of
14.25. confirming previous work (8) that older birds develop higher levels
of antibody than young chicks. Six samples run on S. N. tests for infectious
bronchitis antibody showed that one sample neutralized 10 neutralizing
doses, one sample 100 neutralizing doses, and 4 samples 1000 neutralizing
doses. The numbers, while of necessity small, indicate susceptible birds pro-
duce a higher titre upon vaccination.

Discussion

There is one period in the life of a chicken when carefully controlled
factors result in optimum conditions for life and growth. This period, when
variables are more constant than at any other time, is when the chicks are
being brooded under the hover. It is at this time, when the optimum con-
ditions exist, for any early age vaccinations to be carried out.

With this factor in mind, early field trials of spray vaccination of New-
castle vaccine, or Newcastle in combination with infectious bronchitis
vaccine, were carried out from 2 to 3 days of age in some cases. Recent
work indicates that any age prior to production may be satisfactory for vac-
cination, however.

14

The data presented in this hnlletin was gathered entirely from the
State of New Hampshire, a state on the eastern seal)oard, in which consid-
erable poultry population exists at the present time.

Birds raised on some farms, according to random samples, possess im-
munity to infectious bronchitis at all times. This situation exists because of
a constant exposure to the virus. The majority of breeding farms do not
find this situation to exist, and as a result, a field strain of bronchitis is
given to the birds prior to coming into egg production. The general picture
of breeding flocks in Xew Hampshire is that practically all flocks have been
exposed to bronchitis either by artificial means or by naturally occurring
field strains. Consequently, with very few exceptions, chicks hatched from
these breeding flocks possess a high parental immunity during the first week
of age. Furthermore, it must be kept in mind that such immunity has been
stimulated by an unmodified strain. Luginbuhl demonstrated immunity to
infectious bronchitis at 5 weeks when the chicks were vaccinated at day-old
intranasally with modified infectious bronchitis.

As may be seen from the tal)le. the majority of chicks hatched from
Xew Hampshire breeders possess high parental immunity to Newcastle
disease. The practice of applying Newcastle vaccine by the wing web
method has been a favorite of the breeders of this state. In the presence of
this high parental immunity, however, it has been shown to be possible to
infect chicks with the Bj strain. Hitchner (5) showed that it was possible
to do so at an early age. and Markham and Bottorff (TO) proved that it was
possible to immunize chicks by use of the intranasal or intraocular route in
tlie presence of parental immunity.

Another important factor to be mentioned in connection with the pre-
vious results is that of chronic resi)iratory disease. It has l)een determined
by the oljservation and study of pipped embryos which showed enlarged
hocks and caseous material in the air sacs, also by isolation of CRD agents
from day-old chicks, that the incidence of CRD in the chicks hatched in
X"ew Hampshire is exceedingly high. In those instances in which high mor-
tality was encountered in the field trials, CRD was found to be present in
over 90 per cent of the cases.

While it was originally felt that the chicks to be spray vaccinated must
possess parental immimity to infectious bronchitis, results of field trials and
laboratory trials on susceptible chicks would seem to indicate that parental
immunity, while desirable, is not necessary. From all observations, the in-
dications are that the CRD complex presents the biggest problem in af-
fecting the results of any mass immunization or other vaccination pro-
cedures todav.

IS

Summary

1 . It has been demonstrated that mass immunization of young chicks
with the l^i strain of Newcastle virus, employing spray techniques, is a
safe method, and will produce sufficient immunity to withstand 10 min-
imum lethal doses of Boney Newcastle disease challenge virus at approx-
imately 12 to 16 weeks of age.

2. It has been demonstrated that there is no apparent interference in-
volved in the combination of Blacksburg strain of Newcastle and the UNH
strain of infectious bronchitis viruses when such a combination vaccine is
administered to young chicks utilizing the spray method of mass im-
munization.

3. It has been demonstrated that mass immunization by the spray
methods of a combined Newcastle-bronchitis vaccine is a safe method of
vaccination and will produce sufficient immunity to withstand 10 minimum
lethal doses of Boney Newcastle challenge and 1000 infective doses of field
strain of infectiou.s bronchitis up to approximately 12 to 16 weeks of age.

4. It has been demonstrated that the spray method of mass immun-
ization is an easy and rapid method of vaccination. One man may vaccinate
up to 10.000 chicks per hour, using this method, depending on brooding
conditions.

References

1. Bankowski, R. A. 1950. Further Studies /;/ vitro Cultivated Pheuinoenoeqhalitis

(Newcastle Disease) Virus and Its Use as a Vaccine, Vet. Med. 45: 322-327.

2. Crawley, J. F. 1953. Spray Immunization of Broiler Chicks with Combined

Bronchitis — Newcastle Disease Live \'irus Vaccines. 25th .Annual Conf.
Lab. \\'orkers Pullorum Disease Control.

3. Crawley, J. F. and Fahey, J. E. 1954. The Spray Method for Bronchitis and

Newcastle Disease Vaccination. Southwest Vet. 7.

4. Fabricant, J. 1951. Studies on the Diagnosis of Newcastle Disease and In-

fectious Bronchitis of Fowls. IV. The Use of the S N Test in Diagnosis
of Infectious Bronchitis. Cornell Vet. 41: 68-80.

5. Hitchner, S. B. 1950. Further Observations on a Virus of Low Virulence

for Immunizing Fowls .Against Newcastle Disease (Avian Pneumoencc-
phalitis). Cornell Vet. 40: 60-70.

6. Hitchner, S. B. and Reising, G. 1952. Flock Vaccination for Newcastle Di-

sease by Atomization of the Bi Strain of Virus. Proc. Bk. Am. Vet. Med.
Assoc: 258-264.

7. Hitchner, S. B., and Johnson. E. P. 1948. A Virus of Low Virulence for

Immunizing Fowls .\gainst Newcastle Disease (Avian Pneumoeno-
cephalitis). \'ct. Med. 43: 525-530.

8. Jungherr, E. L. and Terrell, N. L. 1948. Naturally Acquired Passive Ini-

munity to Infectious Bronchitis in Chicks. Am. Jour. Vet. Res. 9:201-205.

9. Luginbuhl. R. E. 1952. Studies on Serologic Diagnosis and Immunization of

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