Eosinophilic Myositis

Eosinophilic myositis is an inflammatory muscle disease in cattle and sheep characterized by greenish/greyish lesions from Sarcocystis spores. It typically affects skeletal muscle, heart, tongue, diaphragm, oesophagus and masseter muscles. Cattle and sheep contract the infection by grazing on pastures contaminated with faeces from hosts like foxes, cats, or dogs, leading to cyst formation in their muscles.

A study by Lieve Vangeel et al (2013) found that the majority (82%) of intralesional Sarcocystis species were found to be S. hominis. However, S. cruzi and S. hirsuta were also found, as well as an unidentified species. It can be concluded that Sarcocystis species present in lesions of Bovine Eosinphilic Myositis are not restricted to one species.

When these cysts break down or are recognized by the immune system, it triggers a strong inflammatory reaction, characterized by a large influx of eosinophils (a white blood cell that protect the body from parasites). Greenish lesions observed during post-mortem inspection frequently suggest the presence of the parasites.

Photo 1: Eosinophilic myositis in skeletal muscle

Inspection procedure

The Australian Standard (AS4696 2023), Schedule 2: Procedures for Post=Mortem Inspection states for cattle and buffalo:

The Australian standard, Schedule 2: Procedures for Post=Mortem Inspection states for sheep and goats:

Observe external surfaces. An equivalent procedure is to remove and discard the head without inspection where tissue, including the tongue are not recovered for human consumption.

The heart, tongue, diaphragm and oesophagus are the most affected organs, and these should be routinely inspected. Although the Australian Standard does not require the observation of the oesophagus in cattle, buffalo, calves or deer unless recovered for human consumption this addition inspection task should be undertaken in cattle from areas where Eosinophilic Myositis is prevalent.

Because skeletal muscles are also affected, a recent MLA-funded project, titled “Risk-based review of post-mortem inspection for bovine eosinophilic myositis (BEM),” suggested adding an extra observation of the major skeletal muscle groups during carcase splitting as part of post-mortem requirements, to help routinely detect Eosinophilic Myositis.

Disposition

Australian Standard AS4696-2023

The Australian Standard does not specifically reference Eosinophilic Myositis but does address Myositis.

The symbol [1] means carcase or carcase parts unfit for human consumption may be recovered for animal food subject to heat sterilisation

DAFF Post-mortem decision notes

Myositis

Carcases showing evidence of muscular inflammation and/or degeneration are dealt with in accordance with the following:

if the lesions are widely distributed and their removal is impracticable, or where there is evidence of systemic involvement, the carcase and its carcase parts are condemned.

If the lesions are localised and the affected carcase parts can be satisfactorily removed, the affected carcase parts are removed and condemned. The remainder of the carcase and its carcase parts may be passed for human consumption.

If the lesions are slight but diffuse, the affected carcase parts are removed and condemned. The remainder of the carcase and its carcase parts may be passed for human consumption.

Where considered necessary, the remainder of the carcase are boned under the direct supervision of an authorised officer.

Carcases and carcase parts (other than those affected by systemic disease) that would otherwise be condemned due to muscular inflammation or degeneration may be saved as animal food.

Author’s comment

The difficulty in making a disposition on eosinophilic myositis is determining when a carcase has localised lesions or systemic lesions and the procedure to follow in making such a determination.

In cases where there are multiple and obvious lesions then the decision is clear – condemn carcase and carcase parts.

However, where there are only a few lesions and they are diffuse (See photo 2) the following procedure is suggested to determine a disposition:

To establish the numbers of lesions, examine in detail the tongue, oesophagus and palpate the heart. In cattle and buffalos observe the cut surfaces of the heart and masseters muscles

Strip the diaphragm and thick skirt and examine the exposed muscles slicing carefully and search for lesions.

Examine the exposed muscles of the neck and hindquarter making small incisions if thought necessary.

If only a few lesions are found, boning under supervision is an option. This requires all meat cuts to be carefully examined often by slicing through the muscles to detect more lesions and their removal. This procedure will damage primal cuts often making the product only suitable for manufacturing meat.

Because of the time and effort required to undertake the “boning under supervision procedures” and the likelihood that the resulting meat will only be suitable for manufacturing product, the economics of the process may make the process uneconomical to undertake.

The term “economic disposition” is often used in these circumstances, and it is really a case of careful judgement and consultation with the owners to make a disposition. In Export premises this will be undertaken by the OPV and in domestic premises, the inspector. In some domestic premises there may not be facilities to “bone out under supervision”.

Photo 2 Eosinophilic myositis in ovines note lesions are diffuse and trimming is not viable.

Cited

Lieve Vangeel , Kurt Houf, Peter Geldhof, Katleen De Preter, Jozef Vercruysse, Richard Ducatelle, Koen Chiers Different Sarcocystis spp. are present in bovine eosinophilic myositis (2013) VETERINARY PARASITOLOGY. 197(3-4). p.543-548