Enzootic Pneumonia
Enzootic pneumonia is an ill-defined term that has been applied to both acute exudative bronchopneumonia and to chronic, non-progressive, pneumonic lesions found at slaughter or necropsy.
Cranioventral lung lobes are typically affected; they are a darker red than the rest of the lung and are consolidated. It is often assumed that viruses or mycoplasma initiated the pneumonia, but that only secondary bacteria such as Pasteurella and Mannheimia spp. and Trueperella (previously Arcanobacterium or Actinomyces) pyogenes can still be isolated from the lungs.Enzootic pneumonia is also a term used to encompass a variety of lung infections occurring in stressed animals. Tlie stress may be provided by malnutrition, shearing, a change in the weather (cold or rain), or the presence of other diseases. Coccidiosis, because of the malnutrition produced by this very common intestinal disease, could be a major predisposing factor for enzootic pneumonia. Increased levels of glucocorticoids then lower the animal’s resistance to infection by adversely affecting both cellular and humoral immunity.
In a scenario similar to the shipping fever complex of cattle, it has been proposed that viruses interfere with macrophage function and with the ability of cilia in the tracheal mucosa to transport inhaled bacteria away from the lungs (i.e., mucociliary clearance; Brogden et al. 1998). A variety of viruses have been incriminated in the process (Daft and Weidenbach 1987); in general, documentation of pathogenicity to goats is scanty.
An RSV distinct from bovine RSV has been isolated from goats with severe coughing, oculonasal discharge, and fever (Lehmkuhl et al. 1980; Martin 1983), as discussed above. Parainfluenza virus type 3 (PI3) (Obi and Ibu 1990) and several serotypes of adenovirus (Woods et al. 1991; Lehmkuhl et al. 1997) may also participate in multifactorial pneumonic processes, but are rarely reported.
Recently, a novel PI3 virus was isolated from goats with respiratory disease in China (Li et al. 2014). Viral antigens of PI3 and RSV, as well as PPR virus, were detected by immunohistochemistry in the lungs of Nigerian goats with pneumonia (Jarikre and Emikpe 2017).Some sheep flocks in the United States have used a half dose of PI3 or IBR-PI3 vaccine intranasally, because parainfluenza 3 is believed to predispose the sheep to pneumonia. All adults are vaccinated, and then lambs are vaccinated as soon after birth as possible (Lehmkuhl and Cutlip 1985; Rodger 1989). There has been apparent efficacy in some flocks, but a practitioner should certainly not recommend such a program in goats without first documenting the activity of the PI3 virus in the disease process to be combated, by either viral isolation or paired serology. It is also undesirable to inoculate goats or sheep with a live IBR vaccine, because of the possibility that they will shed the virus later and thereby infect cattle, or even become sick themselves with the bovine vaccine strain.
Caprine herpesvirus (bovid herpesvirus type 6) has been isolated from the lungs and from nasal swabs of goats dying of M. haemolytica pneumonia (Buddle et al. 1990b). Experimental inoculation of the virus followed six days later by M. haemolytica resulted in pneumonia in five of six goats (Buddle et al. 1990a). Mannheimia alone also caused pneumonia (three of six), but the virus alone caused only catarrhal rhinitis and mild tracheitis. lhus, the role of this virus in producing pneumonia remains uncertain.