R. A. GRIESEMER AND R. L. FARRELL 
957 
Figure 11. — Pulmonary nematodiosis in a calf. The 
bronchi were nearly occluded with masses of long, 
slender parasites (Dictyocaulus viviparous). 
trus ovis. Fly larvae gain entrance directly- 
through the external nares as well as through 
dehorning wounds, periodontitis, and fractures. 
The larvae attach by their mouth parts to the 
mucosa and cause irritation resulting in exces- 
sive mucus secretion and exudative inflamma- 
tion (Figure 12). The infestation is persistent 
and presumably uncomfortable but not of great 
consequence except when it interferes with the 
investigator's experiment. 
Pulmonary Nematodiasis 
Compared with calves, pneumonia is less fre- 
quent and parasitism more frequent in sheep. 
Pulmonary lesions caused by nematodes are 
common and widely distributed in random- 
source sheep. Dictyocaulus filaria causes bron- 
chitis comparable to that caused by D. vivipa- 
rous in cattle. The most ubiquitous of the 
lungworms, however, is Mullerius capillaris. In 
contrast with Dictyocaulus sp., Mullerius sp., is 
found in the alveoli where the adult parasites, 
larvae and ova provoke an enveloping granu- 
lomatous reaction (Figure 13) visible grossly 
as nodules (Figure 14). Older lesions fre- 
quently mineralize. 
Caseous Lymphadenitis 
Caseous lymphadenitis, suppurative inflam- 
mation of lymph nodes caused by Corynehacter- 
ium ovis, occurs as an inapparent infection in 
about 0.1% of sheep. The organisms gain en- 
trance through shearing, castration, or docking 
wounds and produce isolated abscesses in lymph 
nodes (prescapular, mediastinal, and bron- 
chial) and less often in visceral organs in- 
cluding the lung. The abscesses slowly enlarge 
to 10 to 15 cm and when sectioned, the inspis- 
sated exudate has a characteristic concentri- 
cally lamellated appearance (Figure 15) . 
Progressive Pneumonia and Adenomatosis 
Progressive pneumonia is a transmissible and 
infectious disease (probably viral) of range 
sheep. Signs of wasting, occasional cough, and 
^spnea on exertion develop slowly over months 
to years and affected sheep live 3 to 18 months 
after the onset of signs. The principal lesion is 
diffuse interstitial and proliferative pneumonia. 
Other sheep develop adenomatosis which rarely 
metastasizes to the bronchial lymph nodes. It is 
still unknown whether adenomatosis is an ad- 
vanced form of progressive pneumonia or a sep- 
arate entity. Progressive pneumonia accounts 
Figure 12. — Longitudinal section through the head of 
a sheep exposing larvae of Oestrus ovis in the nasal 
cavity and sinuses. 
