Enhancing the defence of the respiratory tract:

Assisting the mucociliary escalator

 

The mucociliary escalator is one of the major defence mechanisms which protect the lung.  If the mucociliary escalator fails, it increases the risk that the normal and potentially pathogenic, inhabitants of the nose, throat and the back of the mouth (nasaophaynx), will descend into the lung, resulting in a potentially life-threatening pneumonia.

 

What is the mucociliary escalator?

Anat Resp cilia normal label.JPG

Electron microscope view of the mucociliary escalatory

Potential pathogens “stuck” at the top of the escalator, waiting to descend if the escalator stops

 

From the nose to the end of the bronchi (inside the lung), the surface is lined with a series of barrier cells.  These cells assist with the collection of material by producing a sticky mucoid substance - the first half of the mucociliary escalator.  This mucus contains chemicals, antibodies and immune cells to destroy any bacteria and viruses that become trapped.  It protects and coats the underlying cells and its sticky nature helps the lungs to remove any dust particles and foreign chemicals in the air.

These barrier or epithelial cells also have small “hairs” or cilia on them, the second part of the mucociliary escalator.  The hairs beat in a well organised manor, to move the mucus (containing trapped particles) – in the nose down to the throat; in the bronchi and trachea (windpipe), up to the throat.  Hence the term escalator. 

At the throat the material first passes over the tonsils and is then swallowed, falling into the stomach, where most particles are destroyed by the stomach’s acids.   As the mucociliary escalator moves particles over the tonsils, the immune system is stimulated to further protect the pig.

 

The mucociliary escalator is so effective, working properly it can remove all particles above 3µm in size.  Only very small particles (about the size of individual bacteria) can actually enter the lung tissue itself.

 

Which part of the lung is most at risk from descending materials?

The mucociliary escalator thus protects the lung from descending material.  But the anatomy of the pig (and other even toed animals) has a peculiarity in that the right apical lobe (at the top of the right lung) is closer to the mouth than the rest of the lung and has its own tracheal bronchi.  The rest of the lung is supplied by the more normal mammalian designed - two main bronchi.

Anat Tracheal bronchus label.JPG

Drawing of the pig’s respiratory tract

The right tracheal bronchus.

 

Thus this upper right part of the pig’s lung will generally be the first area affected with descending infections and this can be a useful guide for the veterinarian when examining a set of lungs.

 

How can the mucociliary escalator’s function be impaired?

Pathogens

There are two major pathogens of the pig which can significantly damage the mucociliary escalator:

·      Mycoplasma hyopneumoniae which can infect a piglet from 14 days of age.  The mycoplasma live on the surface of the cilia and effectively graze the cilia reducing their efficiency.  This resulting damage, termed bronchitis, becomes significant when the pig is around 60-100 kg. As the mucociliary escalator continues to fail, more material from the throat is allowed to descend into the lung.  Eventually the pig can develop full blown Enzootic (Mycoplasma) Pneumonia.  If the pig also has PRRSv, the lung cannot defend itself well against descending particles and the effects of enzootic pneumonia can develop earlier at 40 kg.

·      Swine Influenza virus (all pig types) can infect a naive pig and within hours start damaging the cilia. Swine Influenza can completely strip the cilia revealing the naked underlying surface of the cells.   The damaged mucociliary escalator falters and so becomes unable to defend the lower lung.  Fortunately, in another wise healthy pig, the impact of influenza only lasts a week and the pig will rapidly heal

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Stockmanship

Unfortunately, there are also a number of ways where we can hinder the efficiency of the mucociliary escalator.  These, when combined with a pathogen, can result in a life-threatening pneumonia.

·      Water – decreasing water availability will increase the viscosity of the mucus making it much more difficult to move and thus slows down the mucociliary escalator.

·      Ammonia – will reduce the beating of the cilia as it can act locally as an anaesthetic like substance

·      Dust – as the dust level increases it can overwhelm the mucociliary escalator

·      Room temperature – can both chill the mucociliary escalatory in the nose and in combination with humidity levels above 75% and below 50% change the particle size making it more difficult to for the mucociliary escalatory to clean the incoming air

·      Mycotoxins – as their concentration increases they may affect the pig’s immune system

·      Vaccine programmes – if poor vaccination technique is practiced the mucociliary escalator will not contain the correct antibodies to help fight the descending pathogen.

·      Antibiotic misuse – may interfere with the normal microflora of the nose and throat allowing more significant pathogens a foothold.

·      Gilt litters – piglets born from gilts tend to have a reduced immune system.   If there are more gilt litters than normal there may be more respiratory problems seen in the batch.

·      Stocking density – increases the number of potential pathogens in the pig’s immediate environment, this will increase the challenge presented to the lungs.

·      Hygiene – poor or nonexistent all-in/all-out and pig flow, results in increased numbers of pathogenic organisms in the environment.

·      Flooring – poor flooring is interesting as it allows potentially pathogenic organisms (streptococcus for example) an access point to bypass the mucociliary escalatory and gain entry into the lung tissues via the blood stream resulting in pulmonary abscesses.

 

Of course the mixture of pathogens and poor stockmanship is additive.  The more mistakes one makes, the weaker the pig’s mucociliary escalators efficiency.

 

Poor water flow can have a similar effect to Mycoplasma hyopneumoniae on your pig’s lungs

Overstocking increases the number of pathogens in the immediate pigs environment which may stress the pig’s ability to defend its lungs

 

Summary

Do you put enough effort into the defence of the mucociliary escalator?  Note there are many more ways poor stockmanship can result in pneumonia than there are pathogens.    To reduce the cost of finishing we must put our efforts into a whole pig/building/farm concept. Vaccinating against Mycoplasma may not be enough!