Chronic non-progressive pneumonia of sheep in New Zealand – a review of the role ofMycoplasma ovipneumoniae

Abstract

Chronic non-progressive pneumonia (CNP) is a common disease which affects lambs in New Zealand during late summer and autumn. Mycoplasma ovipneumoniae can be recovered from a high proportion of lesions but it is also present in some normal lungs. Bacteria, especially Pasteurella haemolytica, can also be recovered from more than half the lungs of affected animals. Isolates of M. ovipneumoniae are genetically heterogeneous, as demonstrated by examination of their DNA or total cellular proteins, and are serologically heterogeneous as shown by metabolic inhibition tests. The number of strains present in New Zealand is large and several distinguishable strains can be recovered from each affected lung. Mycoplasma ovipneumoniae has pathogenic potential as indicated by its ability to produce hydrogen peroxide, cause ciliostasis and by its possession of a capsule. Chronic non-progressive pneumonia can be transmitted consistently to over 50% of lambs by inoculation of pooled pneumonic lung homogenate and transmission can be suppressed by broad spectrum antibiotics. In contrast, penicillin does not prevent the development of lesions but diminishes their severity. Pooled lung homogenate treated with digitonin, which inactivates mycoplasmas, has failed to transmit CNP. Pure cultures of M. ovipneumoniae produce only mild lesions in some animals, whereas inoculation with pooled lung homogenate (from which no viruses were isolated) containing mixed strains of M. ovipneumoniae and free from bacteria, is more effective in producing lesions. Research work to date suggests that CNP may be initiated by colonisation of the lung by M. ovipneumoniae which causes ciliostasis and elicits an exudate allowing colonisation of the lungs by bacteria especially M. haemolytica and by other strains of M. ovipneumoniae. The immune response to the initial strain of M. ovipneumoniae may inhibit its replication but would be less effective in inhibiting heterologous strains of the organism allowing their sequential replication. Eventually production of a broad immune response to M. ovipneumoniae would lead to its elimination which in turn would facilitate the elimination of other microorganisms and the resolution of lesions. As natural immunity to CNP occurs within the first year, it may be possible to develop an effective and useful vaccine. Such a vaccine may need to include multiple strains of M. ovipneumoniae.

Mycoplasma ovipneumoniae - A Primary Cause of Severe Pneumonia Epizootics in the Norwegian Muskox (Ovibos moschatus) Population

“…However, based on the histopathological lesions seen in areas heavily infected with M. ovipneumoniae , as also confirmed by IHC, it could be concluded that this agent was a cause of extensive acute to subacute, exudative and in part purely suppurative bronchoalveolar inflammation. This is in contrast to this infection in its reservoir host domestic sheep, in which it normally produces small localized lesions characterized by chronic and proliferative inflammatory reactions [6], [16], [18].The high load of M. ovipneumoniae , as found in neutrophils by IHC in pneumonic muskox lungs indicated that these cells were highly involved in the clearing (phagocytosis) of this minute agent. Like bronchopneumonia in domestic animals [33], the lesions seen in muskoxen were especially pronounced in the cranial parts of the lungs.…”

“…Mycoplasma ovipneumoniae is a sheep-adapted species commonly found in the airways of domestic sheep ( Ovis aries ) worldwide, including Norway [15] – [17]. In this natural host, it normally produces limited, chronic lung lesions and mild clinical signs [6], [16], [18]. However, following stressful events such as crowding and high summer temperatures, severe pneumonia may occur in lambs [16], [17], [19].…”

“…In this natural host, it normally produces limited, chronic lung lesions and mild clinical signs [6], [16], [18]. However, following stressful events such as crowding and high summer temperatures, severe pneumonia may occur in lambs [16], [17], [19]. In some other ovine species, M. ovipneumoniae has been associated with severe fatal pneumonia epidemics following contact with domestic sheep.…”

“…On the other hand, these cases might also reflect infection transmission from chronically infected adult animals (mother cows), established the previous year and maintained throughout the winter. Long duration of infection in chronically infected carrier animals is considered an important way of maintaining the infection in sheep flocks [11], [16], [17], and a mother to offspring transmission has been considered an explanation of lamb pneumonia seen in some bighorn sheep populations the next few years following a mycoplasma epidemic [21], [23].…”

Investigation of severe coughing and ill thrift in adult hill sheep associated with Mycoplasma ovipneumoniae

“…The disease then progresses slowly and becomes evident around 5–10 weeks of age usually accompanied by secondary bacterial infections. There appears to be direct correlation between tissue damage and the number of M. ovipneumoniae organisms present in the lungs (Alley and others 1999). The mycoplasma is transmitted mainly by the respiratory route over short distances, so it is most infectious among housed sheep (Ayling and Nicholas 2007).…”