Handy Hint 3 - ''Stable Virus" by Dr John Kohnke

The infective EHV viral particles inhaled in moist air initially attach to
the nasal and throat membranes and the large throat tonsil area in the rear
of the throat.
The tonsil area is covered in mucus, lymphocytes and monocytes (immune white cells and scavenging ‘phagocytes’) which engulf and attempt to limit the numbers of viral particles being inhaled into the windpipe and lungs.
Young, elderly and horses in hard work often have lower immune reactivity and are unable to limit the number of viral microbes entering, multiplying and being excreted in large numbers from the tonsil area.
This can lead to tonsil immune reaction, which is referred to as Pharyngeal Lymphoid Hyperplasia (PLH) often resulting in affected horses harbouring viable viral microbes on the tonsil surface, to become a long term ‘carrier’.
They can suffer repeated flare-ups when their immune system wanes due to other sickness, hard work or stress during relocation or transport.

Article courtesy of Dr John Kohnke BVSc RDA - Talking Horses newsletter