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

 

Mycoplasma insitu B

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 hyopneumoniaespecific 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 hyopneumoniaespecific 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