Strains of Virus of Foot-and-Mouth Disease Recovered from Outbreaks in Mexico. Pathogenicity and Invasiveness

Abstract

A report on the identification of samples of virus received from Mexico has been made. 1

Before referring to the general effects of the Mexican strains of virus in cattle exposed to infection by inoculation, by contact with diseased cattle, or by the nasal instillation of virus, something should be said about the animals employed in these experiments.

Foot-and-mouth disease is not endemic in Great Britain but is introduced at irregular intervals, outbreaks occurring sporadically. Since the policy of control is by “stamping-out,” that is, elimination of infected and “in-contact” animals by slaughter and burning (or under the exigencies of war, by burial) along with the rigorous application of other disinfection and “stand-still” orders, it is possible only to purchase cattle with a “clean” history as regards foot-and-mouth disease. The cattle used in these experiments were Devon steers between V/2. and 2 years old, in good condition and weighing between 600-800 lbs, and they could be considered as relatively “standard.”

1. Intradermal inoculation Into the tongue. In all 296 cattle have been inoculated with centrifuged suspensions or stock filtrates of the 13 strains of Mexican virus. 184 were inoculated with MP virus, 80 with M.l virus, and the remaining 32 with the other 11 strains. 293 of these 296 reacted well, with local lesions at the sites of inoculation and generalized or secondary lesions at some or all of the usual sites of predilection, feet, and lips, in all cases except 2. These 2 were control animals inoculated with filtrates in an experiment described elsewhere. 2

There were 3 cattle which failed to show lesions at the sites of inoculation. These had been inoculated with similar virus material to that which had produced the disease in other cattle. One of these however subsequently developed lesions at sites other than those inoculated, probably resulting from infection by contact with its box companion which had reacted. The other 2 developed local lesions on the tongue when re-inoculated with the Pirbright stock cattle strain 119 of the Vallée A type.