It is likely that part of the animals selected 
as "recovered” had not been ill but were 
stragglers that remained behind with the 
affected sheep when the still healthy animals 
were removed from the area. It is also quite 
possible that some sheep were sick from other 
causes. 
The outbreak was associated with an unusual 
prevalence of wood ticks, and local residents 
were agreed that jackrabbits and ground 
squirrels occurred in greater abundance than 
had been observed for several years. The 
sheep had been driven through a sagebrush 
area where ticks were abundant. P. tularensis 
was also recovered from jackrabbits, Lepus 
townsendii, found dead in the vicinity. 
Several employees of this ranch were engaged 
in picking ticks from the sheep, in skinning 
dead sheep, and in otherwise handling the sheep 
and contaminated material. About 10 other 
men were engaged in the dipping operations. 
These men worked barehanded with little 
precaution against infection. None of them 
became ill. Seven of them were bled on April 
30 and all gave negative agglutination tests 
for tularemia. A case of tickborne tularemia 
in a 4-year-old child occurred at a nearby ranch. 
Epizootic in Canada 
An outbreak of tularemia in sheep at Whitla, 
southeastern Alberta, Canada, was reported 
by Gwatkin, Painter, and Moynihan ( 9 ), 
who visited the flock on April 25, 1942. Five 
sick sheep were in evidence and a number of 
others had already died. The flock was visited 
again on May 7. The significant history of 
this group as related by the authors was as 
follows: 
The trouble occurred in a group of 850 yearling 
ewes. They had recently been brought from another 
part of the ranch which was covered with low scrub 
and was ideal land for ticks. The land on which they 
were feeding at the time of our first visit also had a 
certain amount of low scrub land. Twenty-four 
animals died and 5 or 6 seriously affected ewes recov- 
ered. Some animals had been observed to have been 
less seriously affected but we were unable to determine 
the number from the owner. They did not go off 
their feet and eventually recovered. We did not see 
any of these mild cases on either of our visits. No 
new cases developed between the first and second visit 
to the ranch. The sheep had been well fed and cared 
for and, with the exception of the affected ones, were in 
excellent condition. There had been no trouble in 
previous years on this ranch. The animals examined 
were all heavily infested with wood ticks ( D . andersoni 
Stiles) and keds ( Melophagus ovinus L.). The sandy 
ground near the waterhole was covered with fully 
engorged ticks and some of these, as well as ticks from 
affected sheep, were collected for examination. On 
our second visit all ticks on the ground had disappeared. 
No drag ticks were taken on the first occasion and, as 
none got on us while walking through the scrub, it was 
evident that they were not plentiful at that time. 
We were unable to collect any on the second occasion 
although the weather was bright and the scrub was 
assiduously dragged for them. 
Infection was demonstrated in the ticks and 
tissues of one sheep, and a high agglutination 
titer was obtained in a serum sample from a 
recovering animal. Twenty-four sheep died in 
the course of this epizootic. 
One of the herdsmen for this flock became ill 
on April 29, 8 or 9 days after he had skinned 
3 dead sheep, and the case was reported as 
ulceroglandular tularemia by Bow and Brown 
(10). This is the only human case we have on 
record that was definitely associated with any 
confirmed outbreak of tularemia in sheep. P. 
tularensis was also demonstrated in ticks and 
tissues of 1 jackrabbit, Lepus toumsendii, and 
ticks from 1 ground squirrel, Citellus richard- 
soni, found dead in the epizootic area. 
Idaho Epizootic, 1949 
The Arco Desert 2 in central Idaho had long 
been recognized as one of the main centers of 
tickborne disease in sheep, presumably tula- 
remia. In the spring of 1927, it was estimated 
that 3,000 to 5,000 sheep died in this general 
area. The first epizootic on this desert in which 
tularemia was definitely diagnosed occurred in 
1949 (11, 12) on a ranch near Rupert, Idaho. 
The history of this episode, which is typical of 
those observed previously, follows (12): 
Lambing in the flock, which then consisted of about 
290 ewes, started at the home ranch near Rupert, on 
December 25, 1948, and continued thfough January 
1949. The flock, which totaled about 500 ewes and 
lambs, was kept at the ranch until April 15 when it was 
turned out on the range, a semidesert area 6 to 12 
miles north of the town of Paul. There were several 
large, abandoned dry-land farms on this range that had 
grown up to cheat grass ( Bromus sp.), but most of the 
2 A large desert area south of Arco, north of Rupert, 
east of Blackfoot, and west of Shoshone, referred to on 
some maps as the Snake River Plain. 
4 
Tularemia in Sheep and in Sheep Industry Workers in Western United States 
