Spirocerca lupi and dogs: the role of nematodes in carcinogenesis

In a recent article, Herrera and Ostrosky-Wegman 1xDo helminths play a role in carcinogenesis?. Herrera, L.A. and Ostrosky-Wegman, P. Trends Parasitol. 2001; 17: 172–175Abstract | Full Text | Full Text PDF | PubMed | Scopus (22)See all References1, reviewed an old question: can some helminths cause cancer? I believe that this is a provocative study, which left us with more questions than answers on the subject. The authors even acknowledged that ‘there is not enough supporting evidence, because molecular observations mostly have been in advanced tumor stages’. The authors stated that it is difficult to study carcinogenesis in animal models because there are no suitable models available. Unfortunately, the authors did not mention the nematode Spirocerca lupi in their study because this nematode is well recognized as a direct cause of malignant neoplasms in dogs.We suggest using S. lupi as a model to study the role of nematodes in carcinogenesis. S. lupi is common in dogs in tropical and subtropical regions, and was first associated with malignant oesophageal tumors in canines 46 years ago 2xObservations on the possible role of malignant esophageal tumors and Spirocerca lupi lesions in dogs. Seibold, H.R. et al. Am. J. Vet. Res. 1955; 16: 5–14PubMedSee all References2, and Bailey (Alabama, USA) later confirmed that S. lupi is a direct cause of fibrosarcomas and osteosarcomas in dogs 3xSpirocerca lupi: the present situation and potential problem. Bailey, W.S. Revista Med. Vet. Parasitol. 1962; 19: 95–101See all References, 4xParasites and cancer: sarcoma associated with Spirocerca lupi. Bailey, W.S. Ann. New York. Acad. Sci. 1963; 108: 890–923Crossref | PubMed | Scopus (51)See all References, 5xSpirocerca lupi: a continuing inquiry. Bailey, W.S. J. Parasitol. 1972; 49: 485–488CrossrefSee all References. Additionally, most cases of oesophageal sarcomas in dogs have been associated with S. lupi infections, and neoplasms can metastasize to the lungs and other tissues 5xSpirocerca lupi: a continuing inquiry. Bailey, W.S. J. Parasitol. 1972; 49: 485–488CrossrefSee all References5.The prevalence of S. lupi in dogs was ∼36% in Mexico City 6xSee all References6, 78% in Kenya 7xSpirocerca lupi infection in dogs in Kenya. Brodey, R.S. et al. Veterinary Parasitol. 1977; 3: 49–59Crossref | Scopus (29)See all References7 whereas, a mean incidence of 28–41% cases of oesophageal neoplasias was recorded in South Africa 8xSurvey of the incidence, diagnosis, clinical manifestations and treatment of Spirocerca lupi in South Africa. Lobetti, R.G. J. S. Afr. Vet. Assoc. 2000; 71: 43–46PubMedSee all References8.The stages of the S. lupi life cycle remain to be clarified in Venezuela (parasitology books cite that the pre-patent period of S. lupi lasts 5–6 months, but in our local veterinary hospital, 3–4 month-old dogs have been diagnosed with clinical or patent infections).We plan to review the life cycle and epidemiology of S. lupi in our laboratory and we wish to encourage researchers at other institutions to undertake research on the biological model of S. lupi in dogs for the following reasons. (1) S. lupi is a proven example of a nematode with carcinogenetic effects in dogs; therefore, experimental work should identify S. lupi excretory or secretory products that can trigger tumor formation. (2) We hypothesized that S. lupi could be a worm with a potent capacity to produce nitric oxide (NO) or other reactive oxygen intermediates, which would explain the development of aneurysms in the aorta of dogs infected with S. lupi. NO production has been reported in nematodes such as Dirofilaria inmitis 9xDirofilaria inmitis and Brugia pahangi: filarial parasites make nitric oxide. Kaiser, L. et al. Exp. Parasitol. 1998; 90: 131–134Crossref | PubMed | Scopus (16)See all References9, which might be important in the pathogenesis of animal diseases and even in parasitic infections. (3) We strongly suspect that S. lupi colonies in the oesophageal nodule might release a bone-growth factor (osteogenic metabolite) that could be responsible for spondylosis lesions often observed at the T5–T10 vertebrae and for hypertrophic osteoarthropathy present in the limbs of dogs infected with S. lupi.