Experiments on infection of cows with typhoid bacilli

Abstract

1. A cow given by the mouth very large doses of virulent typhoid bacilli (275 and 125 thousand millions) on two occasions at an interval of 29 days failed to show signs of infection or to pass the bacilli in faeces or milk.2. Of two-month-old calves, dosed with about 100 ml. ascites broth culture of typhoid mixed with milk, one became infected and typhoid bacilli were grown from the intestine and ileocaecal gland. Both, however, passed typhoid bacilli in the faeces on the first or second day after dosing.3. When large numbers of typhoid bacilli (say, 1–3 thousand millions) were instilled into the udder through the teat canal, excretion of the bacilli in the milk usually ceased within 10 days (fourteen quarters of four cows). In two quarters of one of these cows excretion continued for 25 and 27 days, and in two quarters of another cow for at least 85 days. The procedure usually caused an acute mastitis lasting for a few days, and the ‘H’ and ‘O’ agglutinin titre of the blood rose.4. When large numbers of typhoid bacilli were applied to the teat orifice, even when this had been grossly injured beforehand by slitting the sphincter, there was as a rule only a very transient infection. In eleven cases out of twelve, either the organism could not be found in the milk or was found for 1 day only; in the remaining case there was intermittent excretion for 7 days.5. The strain of typhoid used for most of the above experiments was of high Vi content and was isolated from the carrier involved in the Bournemouth-Poole epidemic of 1936.6. These experiments do not support the view that milk-borne typhoid outbreaks are brought about by an active infection of the cow and suggest that the main object of the epidemiologist must still be the location of the human carrier.7. The chances of typhoid bacilli growing in the milk after its withdrawal from the cow are stressed.This work was rendered possible by financial assistance from the Ministry of Health and from United Dairies Limited. Thanks are due to Dr A. Felix for providing a Vi-rich culture of typhoid, and to Dr V. D. Allison for valuable help in checking the draft paper and making suggestions.