Spirocerca lupi - The silent killer

Spirocercosis is the name given to a disease which unfortunately, is also referred to as 'The Silent Killer'. It is caused by the worm Spirocerca lupi and is endemic in our area. 

Many moons ago when my head carried more hair than my chin, I was part of a team that looked to raise awareness of the disease amongst the KZN Veterinary Community.  For those interested there is a link at the bottom of the article to the publication which carries more detail on the disease. 

The biggest problem we face with the worm is that the onset of clinical signs occurs anywhere from 6-18 months after infestation, and in many of these cases severe complications are already present. These include neoplastic or cancerous transformation of the nodules in the oesophagus, and necrosis and secondary infection of the nodules often resulting in rupture of the oesophagus. In addition to this, between 2 and 12% of cases are reported to present as acute deaths due to aortic aneurysm rupture.  

The good news is, that the widespread use of the macrocyclic lactone contained in dewormers such as Milbemax®, Nexgard Spectra® and Advocate™ have resulted in a significant improvement in the incidence of clinical disease. However, and I will allude to it a little later…the prevalence of the disease still appears to be high.

So why do we need another look at the disease one may ask? There have been a number of very wrong misperceptions, that I have come across in recent times that need correcting.

The first of these is the involvement of the poor Hadeda Ibis. These hapless birds, whose early morning wake up calls have me wondering why I don’t own a shotgun, have been erroneously targeted by many, including a few misinformed veterinarians. Their involvement is no more than the fact that they “poop”, and that Hadeda “poop” seems to be particularly delectable to both our canine friends, and the coprophagic (dung) beetles which are the intermediate host for the worm. Dogs can only be infected by a stage L3 larva and development of the L3 larva from the egg can only happen in the beetle. Dogs acquire the worm by eating the coprophagic beetle when they eat the Hadeda “poop”. They can however, also become infected by eating what we call a paratenic host – rats, birds, frogs, lizards that may have eaten an infected larva. I cannot ever recall anybody telling me their dog ate a Hadeda!

The introduction of a Computed Tomography (CT) Scanner at Westville Veterinary Hospital has also changed our perception of the disease, and this has happened in several ways. The first, is that although we have perceived a reduction in the incidence of clinical disease, particularly the earlier manifestations of vomiting, regurgitation and dysphagia (difficulty swallowing), the disease still appears to be prevalent. We estimate that 60% – 65% of the cases we take to CT where the caudal mediastinum is included in the scan, show evidence of Spirocercosis. This may not all be clinically relevant, but the implication is that the disease is still very much around. 

The second value in having the CT scanner, is that it allows for far better decision making in the treatment of the Spirocerca infected dogs. The case shown in the image above was a Great Dane that presented with a chest full of blood. Based on the radiographs (x-ray) we would have previously given this patient a very grave prognosis – the size of the lesion (red circle) would have a high probability of being neoplastic (cancerous). However, what the CT showed us, was that the bulk of the mass was a haematoma (blood clot) and only a small portion at the cranial edge (marked by the arrows) was the Spirocerca nodule. The Great Dane made a full recovery with medical intervention.

This brings me to another misperception with regards to Spirocercosis and specifically to the prevention of the disease. The only dewormers which have documented evidence to support their use in preventing Spirocercosis are those containing a macrocyclic lactone. This means that the vast majority of dewormers that are used in dogs do not have any effect on the S. lupi. The dewormers containing the macrocyclic lactones MUST be dosed monthly to prevent clinical disease (in other words the oesophageal lesions).  Giving them every 3-4 months will not prevent clinical disease or treat Spirocercosis for that matter.  

Spirocerca lupi - Fascinating new facts and research opportunities [Dr Rick Last Vetdiagnostix - Veterinary Pathology Services. Dr Richard Smith - Westville Veterinary Hospital]

FOLLOW THIS LINK TO READ THE ARTICLE: https://bit.ly/3UXOHdd

Although we are seeing fewer clinical cases Spirocercosis is still very much prevalent.

To prevent clinical disease dog’s, need to be dewormed once monthly with a macrocyclic lactone containing dewormer.

Article written by: Dr Richard Smith