Spirocerca lupi - an unobtrusive time bomb
Dr W J Grobler BVSc
INTRODUCTION
Spirocerca lupi is the name of a slender reddish worm about 40 mm in length that stays in the dog's esophagus. In the past the odd case was seen in Rustenburg, about two to three cases annually, but this has changed dramatically during the past few years.
Since the last six months of 2002 we have seen cases dying from this disease or having to be put down on a more regular basis. This article has as its sole purpose to make dog owners more aware of this problem so that we can endeavor to find a solution. The life cycle, symptoms, diagnosis, treatment and control measures are discussed in some detail below.
LIFE CYCLE
Eggs of Spirocerca are excreted in the faeces of infested dogs whence they are ingested by dung beetles. The immature stages develop further inside the beetles and will infest other dogs eating the beetles. If other animals such as lizards or francolins eat the dung beetles, these animals may also harbour the worms and will infest dogs if eaten by them. Dogs are thus infested by eating dung beetles, lizards and small ground birds such as francolins.
Inside the dog's stomach the worm larvae break out of their cysts and begin their long migration via the arteries to the aorta just behind the heart. They carry on through the wall of the aorta into the wall of the esophagus where they develop into adults thus completing the process. Their life cycle may be completed in about six months, but it may take anything up to two years!
SYMPTOMS
Until the worm larvae have reached the aorta there are no symptoms. Once in the aorta, aneurisms (saclike protrusions in the artery wall) may develop that can lead to thrombosis and embolism of the back legs presenting as pain and lameness in the affected limb. These aneurisms may also rupture leading to sudden death in an affected animal.
Inside the wall of the esophagus the constant irritation of the worms on the tissues leads to thickened growths of the wall. (granulomas) The presence of these granulomas cause regurgitation or vomiting in a large number of cases. Regurgitation is a passive backflow of ingested material from the esophagus, whereas vomiting entails the active contraction of the stomach muscles to expel food already in the stomach.
In exceptional cases tumours may develop in the granulomas due to the constant irritation. These tumours are usually malignant and often spread to the lungs. A very interesting phenomenon that rarely follows these tumours is severe thickening of the fore- and hindlegs. (Marie's disease) (See Fig. 1)
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| Fig. 1: Thickening of the legs similar to that caused by S. lupi. | |
DIAGNOSIS
Most of the symptoms associated with this worm infestation are quite vague and this complicates the diagnosis. In suspected cases X-ray photographs of the chest are taken. If no clear lesions are seen, the animal is fed a contrast medium (Barium) and another set of photographs taken that usually demonstrates lesions between the heart and the diaphragm . (See Fig. 2)
In the radiograph above the white Barium could easily be seen. Note how a lot of Barium is stuck to the left of the Spirocerca lesion. The lesion itself shows up much darker since the Barium flows around it. Some Barium have passed into the stomach on the right.
The best way of making a diagnosis remains endoscopy (a "camera" is passed into the esophagus), but the apparatus is very expensive and thus only available at bigger veterinary hospitals. (See Fig. 3) By examining a stool sample the eggs may be seen, but they are much smaller than other worm eggs and may be missed. It is also possible for thousands of migrating larvae to be present without any eggs being produced.
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| Fig. 3: Four granulomas in the esophagus of a dog as seen with an endoscope. |
TREATMENT
There are only three products that have been registered as effective against this worm (consult your vet about these). Vets will also sometimes use drugs registered for sheep in cases that have just been diagnosed to try and kill the worms as soon as possible. Certain dog breeds are however prone to poisoning by these remedies so they should either be tested for sensitivity or safer drugs may be used. Other drugs may also be used to reduce the regurgitation and the swelling of the esophagus. If tumours have already developed the prognosis becomes much worse as these tumours often are malignant and may spread to the lungs early on.
CONTROL MEASURES
The author has seen dung beetles feeding on dog faeces on many occasions in the middle of the city of Rustenburg. The most important control measure is therefore the removal of dog faeces — preferably on a daily basis. The faeces must be disposed of out of reach of insects. This is especially important with puppies on the premises, since they are rather inquisitive and are more likely to ingest the dung beetles.
Because the life cycle is at least six months, all dogs should be treated with an effective product. Dogs already on oral flea control, could be treated with the combined product at least every six months. Be sure to discuss a preventive program with your nearest vet when you go for the annual vaccinations. With the help of all dog owners we will curb this threatening time bomb!
Acknowledgement for fig. 3: Dept. Small Animal Surgery, Faculty of Veterinary Science, University of Pretoria.