EXPERIMENTAL STUDIES ON THE DURATION OF

Bull. Wld Hlth Org.

EXPERIMENTAL STUDIES ON THE DURATION OF IMMUNITY IN DOGS VACCINATED AGAINST RABIES

H. N. JOHNSON, M.D.

Division of Medicine and Public Health, Rockefeller Foundation, New York, N.Y., USA

SYNOPSIS

The results of laboratory investigations on the duration of immunity in dogsvaccinated against rabies are summarized; the experiments demonstrated that dogs vaccinated with phenol- treated killed-virus vaccine show a high degree of immunity at one year after inoculation and that the immunity produced with the Flury-strainlive-virus vaccine is superior to, and oflonger duration than, that obtained with chemically-treated brain-tissue virus vaccine.

A study of the susceptibility of dogs to street-rabies virus at one year afterasingle subcutaneous injection of killed-virus rabies vaccine has been reported.' The details of this study are summarized in table I. The dogs were from 9 to 38 months of age at the time of vaccination. Vaccinated and control dogs were selected so that each group would have the same age-distribution. The vaccine was a single lot-number of sheep-brain vaccine, a 20% brain-tissue virus suspension in physiological salt solution containing 0.5% phenol. The vaccine had beenincubated to eliminate the infectivity of the fixed rabies virus. Mice injected intracerebrally with this vaccine did not develop rabies. The immunizing potency of the vaccine was satisfactory, as determined by mouse potency test.

Each of 52 dogs received a single dose of 5.0 ml of the rabies vaccine by subcutaneous injection. One year later the vaccinated dogs and 52 control dogs were tested for susceptibility to rabies by intramuscular in- oculation with a street-rabies virus obtained from thesubmaxillary salivary glands ofadog that had died of rabies. This was a standard street-rabies virus kept in sealed glass ampoules in a carbon dioxide dry-ice chest. The stockvirus wasdiluted so as toapproximate to the maximum virulence of naturally-infected dog saliva. Each dogwas givenan injection of 0.125 ml ofa 10-2dilution of thesalivary-gland tissue virusin each masseter muscle.

Physiological salt solution was used as the diluent, and the testvirus hada consistency similar to that of dog saliva. Vaccinated and control dogs

1Johnson, H. N.(1945) Proc. US Livestk sanit. Ass.99;

287 -725-

TABLE I. SUMMARY OF THE STUDY OF THE DURATION OF IMMUNITY FOLLOWINGTHE SINGLE-INJECTION METHOD OF CANINE-RABIES VACCINATION

Control dogs

15-3-44 weight in pounds neutralization test result of test

dog age (equivalent inoculation

No. (months) in kg) 1944 1945 21-3-45

2024 9 14 (61/2) - Rabies

1878 11 18 (8) - - Rabies

1880 11 12 (51/2) - - Rabies

1884 11 21 (91/2) - Rabies

1963 11 20 (9) - _ Rabies

1934 12 32 (141/2)

2052 12 30 (131/2) + +

1809 13 11 (5) - Rabies

1813 13 12 (5/2) _ - Rabies

1817 13 12 (51/2) Rabies

1915 13 12 (51/2) ^- Rabies

1874 14 12 (51/2) -Rabies

1957 15 21 (91/2) - - Rabies

1959 15 10 (41/,) - - Rabies

1965 15 21 (91/2) ^- - Rabies

1971 15 23 (1072) - - Rabies

2028 15 32 (141/2) + +

2033 15 26 (12) - _ Rabies

2036 15 15 (7) - Rabies

1893 16 21 (91/2) ^- - Rabies

1941 16 24 (11) - Rabies

1949 16 10 (472) + - Rabies

1952 16 24 (11) - - Rabies

1954 16 30 (131/2) - Rabies

1920 17 20 (9) - - Rabies

1924 17 19 (81/2) _ Rabies

1926 17 21 (972) _

1929 17 13 (6) - _ Rabies

1861 18 23 (10'/2) + +

1863 18 20 (9) _ Rabies

1866 18 9 (4) - Rabies

1872 18 25 (111/2) Rabies

1889 18 27 (12) - Rabies

1891 18 22 (10) - Rabies

1895 18 31 (14) - -

1898 18 36 (167/2) -

1900 18 18 (8) _ _ Rabies

1903 18 13 (6) _ - Rabies

2054 18 20 (9) + -

2056 18 47 (211/2) + +

1842 19 19 (81/2) _ - Rabies

1857 19 21 (91/2) _ _ Rabies

1859 19 30 (131/2) _ - Rabies

1974 20 22 (10) _ - Rabies

2040 20 41 (181/2) _

2042 21 27 (12) - - Rabies

1821 22 16 (7) _

1922 23 17 (772) _ _ Rabies

1846 25 34 (151/2) _ _ Rabies

1945 28 36 (161/2) _ _ Rabies

1824 35 27 (12) _ _ Rabies

1762 38 37 (17) _ - Rabies

TABLE I. SUMMARY OF THE STUDY OF THE DURATION OF IMMUNITY FOLLOWINGTHE SINGLE-INJECTION METHOD OF CANINE-RABIESVACCINATION

Vaccinated dogs ^on 17-3-44 dog

|15-3-44

No. age

(months)

1877 11

1879 1 1

1883 11

1960 1 1

1881 12

1950 12

1808 13

1811 13

1816 13

1923 13

1868 14

1873 14

1956 15

1958 15

1964 15

1966 15

1968 15

1970 15

1936 16

1939 16

1942 16

1944 16

1946 16

1948 16

1913 17

1916 17

1918 17

1919 17

1925 17

1928 17

1930 17

1862 18

1885 18

1890 18

1892 18

1896 18

1899 18

1901 18

1905 18

1906 18

1843 19

1856 19

1858 19

1836 20

1972 21

1932 22

1921 23

1864 24

1894 24

1953 28

1804 33

1773 37

eingponds

(equivalentⁿ inoculation

inkg) 0 1 month 6 months 12months 21-3-45 14 (6/2)

8 (31/2) 14 (61/2) 1 1 (5) 20 (9) 1 1 (5) 12 (51/2) 12 (51/2) 10 (47/2)

14 (6½/) 17 (7'/2) 1 7 (7/2) 29 (13) 23 (10/2) 12 (51/2) 23 (101/2) 34 ( 15/2) 15 (7) 27 (12) 19 (81/2) 27 (12) 15 (7) 15 (7) 11 (5) 24 (11) 46 (21) 23 (10/2) 15 (7) 20 (9) 46 (21) 32 (1472) 27 (12) 18 (8) 25 (111/2) 18 (8) 24 (11) 1 8 (8) 29 (13) 15 (7) 15 (7) 11 (5) 35 (16) 1 8 (8) 22 (10) 39 (17/2) 37 (17) 31 (14) 38 (17) 25 (111') 38 (17) 26 (12) 32 (1472)

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wereinoculated alternately. When all of thedogs had beeninoculated, the test virus was titrated in mice and this showed that each dog received approximately 4,700mouse intracerebral median lethal doses (LD50). The dogs were held for observation for three months after inoculation with street-rabies virus. Ofthe 52 vaccinated dogs, 6 (11.5%) died of rabies, as compared with 41 out of 52(79%) control dogs.

The blood-serum of the dogs was tested for rabies-virus neutralizing substance. This test was recordedas positive ifmore than50% ofthe mice survived intracerebral inoculation with a mixture of equal parts of dog serum to be tested and a standard rabbit fixed-rabies-virus suspension diluted to make a final concentration of 100 LD50 per 0.03 ml. Nine of the vaccinated dogs were positive before vaccination. Thirty-six were positive atone month and 39 at six months after vaccination. At 12 months after vaccination only23 of the 52 vaccinateddogs werepositive. None of these developed rabies. Sevencontrol dogs werepositive atthe beginning ofthe study; four remained positive, and these did not develop rabies.

The studies of the duration of immunity to rabies in dogs vaccinated with phenol-treated killed-virus vaccine and Flury-strain chicken-embryo- adaptedlive-virus vaccine, reported by Koprowski &Black,2aresummarized in table II. This confirms the observation reported previously3 that dogs vaccinated with phenol-treated killed-virus vaccine show a high degree of

TABLE II. RESULTS OF CHALLENGE INOCULATION WITH STREET VIRUS OF DOGS VACCINATED WITH RABIES VACCINES

Interval Results of challenge

between

vacci- rbe iu

nation Vaccine number of dogs rabies virus

and dayof death isltdfo

challenge inocu- dead % afterchallenge brain salivary

lated dead tissue gland

Flury-strain living virus 25 0 0 - -

1 year Phenolized horse brainorigin 22 3 14 18, 21,260 3 1 Non-vaccinated controls. 25 18 72 15, 18, 18,18, 18, 18 16

18,18, 21, 23, 25, 25, 25,26, 27, 29, 29, 33,33

Flury-strain living virus 25 3 12 21, 22,24 3 0

2 years Phenolized horse brain origin 19 8 42 14, 16,17,18, 18, 6 0 19,20,33

Non-vaccinated controls . 23 21 91 13, 15, 16,16, 16, 21 11 17, 17, 17, 17, 18,

18, 18, 19,20,21, 22, 22, 22, 22, 22, 23

2Koprowski, H. &Black, J.(1952)Proc.Soc. exp.Biol. (N.Y.)80,410

3Seefootnote 1, page725.

immunity to rabies at one year after vaccination. The immunity produced by vaccination with the Flury-strain live-virus vaccine is superior to, and of longer duration than, that obtained with the chemically-treated brain- tissue virus vaccine.

RESUME

Des experiences ont ete entreprises en vue de determiner la duree de 1'immunite obtenue chez 52chiensde 9-38 mois, recevant par voie sous-cutanee 5 ml d'un vaccin contenant 20% desuspension cerebrale dans la solution physiologiquepheniquee'a 0,5%, dont le pouvoir immunogene avait ete verifie sur la souris. Au bout d'une annee, les chiens ontrequune dosed'epreuve de virus des rues correspondanta4.700DL50pourlasouris, injectees par voie intracerebrale. La mortalite chez les chiens a et& de 11,5 % (contre 79 % chez les temoinsnonvaccin6s). Comparant cesobservations acellesqu'il a faites ante- rieurement etacelles d'autres chercheurs, I'auteurconclut que les chiens qui ont recu duvaccinpheniquepresentent uneimmunit6elev6euneannee apres la vaccination, mais quela souche Fluryconfereune immunite plus elevee et plus durable que le vaccin de tissu cerebral trait6par une substancechimique.

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