Cross Immunity Experiments in Monkeys Between Variola, Alastrim and Vaccinia

Abstract

PART I. VARIOLA AND VACCINIA IN spite of the voluminous literature, much of it of a polemical rather than scientific nature, on the immunity relationships between variola and vaccinia, comparatively little work has been carried out on experimental animals, and the results of different workers are not altogether concordant. Even in the important article by Blaxall (1930) in the System of Bacteriology only a few lines were devoted to a discussion of the existing experimental evidence, and also in the more recent article by Gastinel (1938) this particular problem has been very briefly treated. PRESENT EXPERIMENTAL WORKOpportunity was taken during an outbreak of virulent smallpox in the Gezira cotton-growing area of the Anglo-Egyptian Sudan in 1938 to collect variolous material from different patients, and to inoculate a series of monkeys. TECHNIQUEThe contents of the vesicles or pustules were aspirated into capillary tubes, which were immediately packed in ice in a vacuum flask and brought directly to Khartoum, 80 miles from the epidemic zone. The capillary tubes with the pus were ground up in a mortar with distilled water (pH 7.0), the suspension lightly centrifuged to throw down the powdered glass, and the turbid supernatant fluid pipetted off and stored in the freezing chamber of a refrigerator. Inoculation was made on to the scarified bellies of monkeys (Cercopithecus sebaeus), the amount of inoculum and area varying in different animals, and the subsequent immunity tests were carried out with both vaccinia and variola.Details of the treatment of each animal are given in the following notes:

Smallpox and Related Poxvirus Infections in the Simian Host

“…In other studies with variola and alastrim viruses (40), it was also found that immunity was not fully reciprocal, but that the degree of protection induced by alastrim was greater than that by variola. This finding was of considerable interest, because the variola strain used was the most virulent for monkeys isolated in the Sudan, and the alastrim was incapable of producing more than a local reaction.…”

“…In general, laboratory techniques for distinguishing between the viruses of variola and alastrim have failed to reveal constant differences with regard to the histology of skin lesions (21,28), the lesions produced on the chorioallantoic membrane of embryonated eggs (28), cross-immunity experiments in monkeys (40), serum-neutralization, complement-fixation, and hemagglutination-inhibition tests (25,27,47), by the double-diffusion precipitation technique (35), and the use of laboratory animals (22). Within recent years, however, the findings from studies of the behavior of smallpox and alastrim viruses in embryonated eggs offer a means of differentiating them.…”

“…In a series of cross-protection tests between (40) indicated that, although cross immunity was strong, it was not completely reciprocal in most cases. The protection induced by vaccinia virus against both viruses was complete; that of variola was complete against itself, but varied from strong to complete against vaccinia.…”

“…When the cutaneous route was used, the production of immunity by variola virus against vaccinia virus was directly related to the extent of the primary reaction and for complete protection a well marked reaction over a considerable area of the skin appeared to be essential (40). The larger the area, the greater the possible im-munizing dose, and the greater was the chance of a strong reaction.…”

Monkeypox virus.

“…As a rule, the disease is generalized with the development of a rash of varying severity in different species of primates. In almost all respects it resembles naturally occurring variola in man (25,65) and experimental variola in monkeys (14,35,37,42,47,59,76). The incubation period of the disease in experimentally infected animals has varied from 7 to 14 days in cynomolgus and rhesus monkeys, and in baboons (40,73,75).…”