Q: How dangerous is Spirocerca lupi?
A: Spirocerca lupi is a nematode (roundworm) which is found primarily in dogs (but also wild carnivores) and occurs throughout the world in warmer to temperate climates. It is not a new parasite but seems to be more prevalent in recent years in South Africa, including the Highveld area.
The adult worm lives in the oesophagus of dogs where it embeds itself in the oesophageal wall and forms large nodules which may later become cancerous. Infected dogs will usually have two to four nodules, but many more are also possible. While in the oesophageal nodules, the adult worm produces eggs which are shed in the dog’s stool. The eggs are then ingested by dung beetles which act as the intermediate host. The dog can be infected by directly eating the dung beetle, or eating a lizard or bird who has ingested an infected beetle. The dung beetle implicated is the small scarab beetle (a few millimetres in length) and not the traditional bigger ones which are several centimetres long.
Because Spirocerca lupi may cause aneurisms, affected dogs may die within seconds from massive internal haemorrhage. Spirocerca lupi is a common cause of sudden, unexplained death in areas where the worm occurs. Most frequently, however, they just cause lumps in the oesophagus which slowly grow bigger.
Initially, when the lumps are about pea-sized, they do not cause any problems and the dog shows no visible signs of infection. As the lumps grow bigger the dog may show a poor appetite, lose weight, start regurgitating food after meals, gag, show a low-grade fever and appear listless. Anaemia and the presence of dark to black stool due to the presence of half-digested blood in the stool (melaena) may also be noted in advanced cases. Although most worms will migrate to the oesophagus as final destination, in rare cases the worm migrates to other sites (called aberrant migration) and may end up in the brain, eye, spinal cord, skin or any other tissues, causing a variety of symptoms depending on the location. In long-standing cases, the lump in the oesophagus may become neoplastic (cancerous).
Advanced cases with large granulomas respond poorly to treatment and if the lump has progressed to cancerous transformation, treatment is not possible. Advanced cases may therefore have to be euthanised. Surgical excision of the nodules has been attempted but is associated with high mortality rates and no longer recommended. Treatment of infected dogs is the only option in dogs not euthanised as all untreated dogs usually die from complications. Earlier cases may respond to some formulations containing avermectin. Treatment may stretch over a period of six months or longer. Generally, the earlier the treatment commences, the higher the success rate.
Dr KGM De Cramer