Enzootic (Mycoplasma) Pneumonia

Also called		Virus pneumonia. Mycoplasma pneumonia. EP. PRDC – Porcine Respiratory Disease Complex.
Causal agent		Mycoplasma hyopneumoniae. A mycoplasma does not have a cell wall
Occurrence		A disease commonly seen in growing and finishing pigs Note enzootic pneumonia may not require Mycoplasma hyopneumoniae – it just describes the clinical condition
Complicating factors in the clinical expression of enzootic pneumonia
Bacteria		There are a number of bacteria and mycoplasma which can infect the lung, particularly after the effects of the mycoplasma on the mucocilary escalator. These include pasteurella, streptococci and Actinobacillus pleuropneumoniae (APP), Actinobacillus suis, Haemophilus parasuis (Glässers disease) also plays a contributing role in post-weaning respiratory disease.
Viruses		These include PRRSv, Swine Influenza, Circovirus II and Porcine Respiratory Coronavirus (PRCV). Aujeszky’s Disease (Pseudorabies) and Classical Swine Fever may play a pivotal role.
Others		Parasites- Ascaris, lungworm
Environmental factors		There are many factors for which the stockperson is responsible. These include:
Air		Excessive 24 hours temperature variations. Draughts. High ammonia concentrations
Floor		Overstocking. Rough floors
Water		Poor water flow. Insufficient drinkers
Feed		Dusty feed. Poor feed availability
Clinical signs		Coughing, with or without fever (with fever 40.5 to 41C implies a complicated enzootic pneumonia), laboured breathing, variable growth rates, unthrifty appearance, reduced appetite and increased post-weaning mortality. Classically the clinical signs are seen in pigs of 60-80 kg, but in complicated cases can occur much earlier. Note the piglet may be infected from 14 days of age without any clinical signs. If in naïve herds break, sows may abortion due to pyrexia.
Transmission		The disease can move via the air from infected farms to adjacent farms within 3 km. On infected farms, the disease is transferred from the sow/gilt to her offspring, sows may still have mycoplasma in her nose at parity 8. Infected pigs spread the disease by droplet spread from nose to nose contact and coughing pigs. One cough can spread the disease 4 metres, assuming the mycoplasma can survive the cough
Incubation		With high level of infection, incubation takes 5 days. With a moderate level of infection incubation may take 4 to 6 weeks
Effects of enzootic pneumonia		Depending on the extent, enzootic pneumonia can reduce daily liveweight gain by 17% and increase feed conversion by 14%. In other cases causes death. Enzootic pneumonia can also have a significant effect on PRRSv infections making them more serious to the weaner by encouraging macrophages into the lung.
Pathogenesis	Mycoplasma hyopneumoniae graze the cilia on the trachea and bronchi (the windpipe). The cilia are important as they help to protect the lung from particles (dust and disease). Once the disease enters the lung it causes areas to collapse and the pig progressively becomes short of air. The collapsed areas become infected with other diseases and the pig finally succumbs to the disease load. The mycoplasma has an effect on macrophages and reduces their ability to kill and digest other pathogens. There is a significant effect of coinfection risk with PRRSv and Aujeszky’s disease which will potentate the clinical signs
			The diseased collapsed areas are darker (arrow) than the normal light parts of the lung	The normal lung floats while the diseased lung sinks
Diagnosis	Slaughterhouse examination
	Examination of the serum by ELISA and PCR. Immunohistochemistry of tissue sections
Treatment and control	Greater than 70% of normal health herds are infected by Mycoplasma hyopneumoniae. Because the disease is so widespread, control and treatment is complicated. Elimination of Mycoplasma hyopneumoniae – specific programmes
EP - ve herds	Where herds are set up from EP-ve pigs, these herds have much less problems with respiratory disease. Maintenance of the EP status takes a lot of time and planning. Sitting of such a pig farm is fraught with difficulty as the mycoplasma can spread 3km through the air. Note the proximity of major roads. On negative units, it still may be worth vaccinating gilts to protect the adult herd from an abortion storm and pig flow disruption.
EP +ve herds
Eradication	Difficult both practically and economically as herds can be re-infected quickly. May even be impossible on certain units. Tulathromycin may be used in an elimination programme Elimination of Mycoplasma hyopneumoniae – specific programmes
Antibiotics	Antibiotics limit the effects of the disease. However, subsequently to viruses becoming involved in pig respiratory disease, antibiotics are proving less effective
Herd management	Improvements in the environment of the pig greatly help to reduce the stress factors. In particular improvements in ventilation and a reduction in the stocking density should be attempted
Disease management	Partial depopulation, cleaning and repair of the growing/finishing phase has helped considerably. This may be combined with all-in/all-out, effective pig flow, batching systems and 2 or 3 site production systems
Vaccination	Mycoplasma hyopneumoniae vaccines significantly help to reduce the effect of the disease. The vaccine is administered between 7 to 10 days of age and at weaning (21-28 days), but awareness need to be made regarding the maternal antibody levels provided from the sow Do not vaccinate the sow to raise maternal antibodies. Vaccinate gilts and boars as part of their introduction period.
Zoonotic Implications
	None

Enzootic (Mycoplasma) Pneumonia

The approximate relationship between lung damage/scoring system

at slaughter at 95 kg and daily liveweight gain and food conversion ratio

	Lung Lesion	DLW Reduction		FCR increase
		%	gr./day	%	Value
	0/55 NEGATIVE	0	0	0	0
	2/55 MILD	-4	-25	0	0
	10/55 MILD	-7	-50	+5	0.15
	15/55 MODERATE	-11	-80	+8	0.25
	20/55 MODERATE	-15	-100	+11	0.35
	30/55 SEVERE	-20	-130	+14	0.40
	55/55 SEVERE	-22	-560	+17	0.50

The estimates of reduction in DLW and FCR is based on Straw 1989 using pigs with 700g/day over the finishing period and a FCR of 3.

The lungs are shown from the ventral, with the intermediate lobe superimposed for completeness

The severity of the lesion may indicate stage of infection. Therefore, an individual pig with a severe lesion may have been only recently affected and have excellent growth rates. This can be compared with the growth rate of chronically affected (smaller lesion) pigs.

Specific Mycoplasma hyopneumoniae elimination programmes

Partial depopulation

Segregated early weaning and medication programme