Pneumonia may be defined as inflammation of lung tissue.
Pneumonias have been classified in various ways, e.g. according to the area or tissue involved, or according to lesions, or causes.
Lobar pneumonia is that in which a whole lobe is involved; in lobular pneumonia the inflammation is less localised and more patchy. Broncho-pneumonia is that in which the inflammation is concentrated in and around the bronchioles leading from the bronchi. Pleuro-pneumonia, as the name suggests, involves the pleural membranes as well as the lung itself. Interstitial pneumonia affects the fibrous supporting tissue of the lung rather than the parenchyma though consolidation of the latter can then occur. (See also LUNGS, DISEASES OF for lesions.)
Pneumonia, which can be acute or chronic, may — as mentioned above — also be classified according to causes, e.g. viral, mycoplasmal, bacterial, mycotic, parasitic and non-infective. It must be borne in mind, however, that infections may be mixed and changing. (See RESPIRATORY DISEASE IN PIGS for an explanatory diagram.)
Pneumonia may arise from a primary viral infection, with complications caused by secondary bacterial invaders, as in canine distemper. Some viruses and bacteria depend upon each other, as explained under SYNERGISM. The infection may be a very mixed one, e.g. in ENZOOTIC PNEUMONIA OF PIGS. Bacterial pneumonia may be acute, e.g. KLEBSIELLA infection, or of a chronic suppurative type, e.g. TUBERCULOSIS.
The main effect of pneumonia, whether through the presence of exudate in the bronchioles and alveoli, or destruction of areas of lung by abscess formation or consolidation or hepatisation, is that the normal exchange of carbon dioxide for oxygen is impaired and impeded. The animal has to struggle for breath to obtain sufficient oxygen.
Signs With less oxygen available to the red blood cells (and hence to the organs and tissues) at the normal respiratory rate, the animal accordingly needs to breathe faster. This increased respiratory rate (tachypnoea) is therefore a main symptom. The breathing may also become laboured and painful (dyspnoea). Fever is usually present, with accompanying dullness and loss of appetite (but see under CALF PNEUMONIA for an exception to this). There is often a cough, though this is not an invariable or attention-catching symptom.
In cattle, most cases of viral pneumonia, uncomplicated by secondary bacterial infection, show areas of collapse in the lungs, emphysema of the apical lobes, some in the cardiac lobes but little in the diaphragmatic lobes, with little or no exudate. An acute pneumonia may develop in some cases of infectious bovine rhinotracheitis. (See RHINOTRACHEITIS.) Bovine syncytial virus is another important pathogen, causing coughing, oedema of the lungs, consolidation and emphysema. (See also CALF PNEUMONIA.) In horses, pneumonia in young foals may be caused by equine herpesvirus 1. (See also SWINE PLAGUE.)
An example of this is fully described under CONTAGIOUS BOVINE PLEURO-PNEUMONIA – a disease not normally present in the UK. Mycoplasma bovis and M. dispar are primary pathogens in the UK. The latter may cause CALF PNEUMONIA of a mild type except for the harsh cough. (See also under MYCOPLASMA.)
Bacterial toxins may have an important additional effect in this. In cattle, Pasteurella haemolytica can be a primary cause of pneumonia, typically producing much exudate as well as a secondary invader. In horses Corynebacterium equi causes a suppurative bronchopneumonia in foals, and in adult horses a suppurative pneumonia may also occur during the course of strangles.
Streptococcus pneumoniae and Staphylococcus aureus are other important secondary invaders of damaged lungs.
This may be an extension of PARASITIC BRONCHITIS in calves, caused by the lungworm Dictyocaulus viviparus. Autopsy findings include dark red consolidation of some lung lobes. In pigs, lungworms (Metastrongylus) are also a cause of pneumonia.
Mycotic (fungal) pneumonia
Mycotic (fungal) pneumonia is caused by Aspergillus species, and also by Candida albicans. (See MONILIASIS.) The latter may be associated with oedema of the lungs, in both mammals and birds, and may follow the use of certain antibiotics. (See also PHYCOMYCOSIS.)
Allergic pneumonia ( see FARMER’S LUNG’ which affects cattle also)
Non-infective pneumonia can result from the action of certain poisons, e.g. PARAQUAT, ANTU, and phenolic sheep dips (see DIPS), as well as from aspiration pneumonia. The latter may result from milk ‘going the wrong way’ in bucket-fed calves, and also from medicines administered to animals by stomach tube passed in error into the trachea instead of the oesophagus (fortunately a rare occurrence!). Aspiration of vomit is another example.
Non-infective pneumonia quickly becomes infective, as micro-organisms take advantage of the inflamed mucous membranes. The animal becomes suddenly dull, uninterested in food, feverish, and may show signs of chest pain. Death can be expected within 72 hours, and autopsy findings may include areas of necrosis and abscess formation.
Treatment of pneumonia
Separate affected animals, provide good-quality feed in a well-ventilated environment, free from draughts, and good bedding. Appropriate antibiotics, sulfa drugs, and trimethoprim may all be of service. Heart stimulants, the administration of oxygen, and possibly diuretics in the case of oedema, may be indicated. Anti-inflammatory drugs, e.g. flunixin, may help in the acute stage. The one golden rule in the treatment of pneumonia in all animals is: ‘Do not drench.’ Medicines should be administered by injection, in the food, or perhaps as an electuary. (See also NURSING.)
Pneumonia in Calves
(see CALF PNEUMONIA)
Pneumonia in Cats
Bronchopneumonia can be a complication of feline viral rhinotracheitis in young cats.
In older cats tuberculosis is still sometimes a cause of disease of the lungs, though with nearly all milk now pasteurised in EU countries, feline TB is no longer at all common. It can, however, result from a cat eating TB-infected prey.
A granulomatous pneumonia is caused, rarely, by Corynebacterium equi. Theoretically, a stable cat would be more prone to it.
Pneumonia in Horses
In a USA study, anaerobic bacteria were isolated from pleural fluid or tracheobronchial aspirates obtained from 21 of 46 horses with bronchopneumonia. Bacteriodes oralis and B. melaninogenicus were the species most commonly isolated (9 and 5 horses, respectively). Other Bacteriodes species were cultured from 12 animals and Clostridium species from 8. A putrid odour was associated with the pleural fluid and/ or breath of nearly two-thirds of the horses from which anaerobes were isolated. The prognosis was significantly poorer in cases with anaerobic infections; 14 of the 21 horses involved either died or were euthanased. (See also under FOALS, DISEASES OF).
Another cause is Corynebacterium equi, which can also infect cats.
Pneumonia in Pigs
Actinohacillus (Haemophilus) pkuropneumoniae is a major cause of pneumonia in pigs. (See RESPIRATORY DISEASE IN PIGS.)
For the most common form of pneumonia in pigs, see under ENZOOTIC PNEUMONIA. (See also SWINE PLAGUE.)
Pneumonia in Sheep
In Britain, pneumonia caused by Pasteurella haemolytica has become more frequent. This organism commonly lives in normal sheep, and causes disease only when the animal’s resistance is weakened by bad weather, transport from one farm to another, movement from a poor to a richer pasture, or perhaps by a virus. In some outbreaks, where the disease takes an acute form, a sheep which seemed healthy enough in the evening may be found dead in the morning. Usually, however, the shepherd sees depressed-looking animals with drooping ears, breathing rather quickly and having a discharge from eyes and nostrils, and a cough. Death often occurs within a day or two. The last sheep to be involved in the outbreak tend to linger for several weeks, looking very tucked-up in the meantime, with a cough and fast breathing. Antisera and vaccines are available for treatment and prevention.
Another cause of pneumonia in sheep is Chlamydia psittaci. (See also HAEMORRHAGIC SEPTICAEMIA, which occurs in the tropics; PARAINFLUENZA 3 VIRUS; MAEDI/VISNA.)