The Curious case of Transmissible Venereal Tumor in Dogs’ by Dr. S. Warson Monsang Associate Professor, Department of Surgery Tripura Veterinary College
One of the strangest living things on the planet started as a dog, but has turned into something else entirely.
It originated somewhere in Asia about 6,000 years ago, when a cell in the genitals of an unknown dog developed mutations that allowed it to multiply uncontrollably to be callled as ‘tumor or cancer’.
But unlike almost every other cancer, which ultimately goes down with its host, this one did not. Somehow, it gained the ability to spread from one dog to another through sexual contact. And in doing so, it achieved a kind of immortality. The original dog is long gone, but its contagious cancer – known as canine transmissible venereal tumor, or CTVT – lives on, having hopped around the world on the junk of humanity’s best friend”.
In every corner city of Agartala, pockets of canine population roaming day and night along the streets of the city are mainly dependent on the availability of foods from the restaurants, hotels, vendors and many individuals who selflessly offered them on daily basis. At present, these homeless dogs are uncontrollably increasing in their numbers at an alarming rate. Statistically, India accounts for about 23-43 % of the total number of tumors in canine population because of uncontrolled sexual behavior and a large stray dog population.
Generally, these dogs are seldom affected with one or more ailments because of their habits of staying around the dirty places, streets and roaming around garbage in search of their food which is essentially required for their stomach. Considering the health point of view, majority of these dogs suffered from various forms of skin diseases, severe wounds from trauma or accident, bone fracture either due to automobile accidents or infliction, ocular or eye problems, tumors and most importantly a fatal and transmissible form of a genital disease called as TVT or CTVT (Transmissible Venereal Tumor or Canine Transmissible Venereal Tumor; it has also may other synonyms).
By transmission, it literally means the diseased dog can spread the infection to other healthy dogs which has the potential to spread further to larger population by transfer of living cancer cells between dogs when comes into contact (touching or licking) or through sexual transmission. TVT is more commonly observed in the free-roaming, stray, sexually active dogs and the most affected site for this tumor is the external genitalia of both sexes, appearing as a cauliflower-like growth or nodular, lumpy, pedunculated type of growth which sometimes is painful, smelly, bleeding and the dog’s gradually becoming weak and lethargic if remained unattended and untreated leading to death.
In recent times, research has helped the scientists to discover that CTVT is evolving in a different way than human cancers. TVT or CTVT is considered the oldest documented animal cancer, estimated to be 11,000 years old and with over 2 million mutations. An international team of researchers found that it may have originated somewhere in central or north Asia some 6,000 years ago, and had spread to different continents and countries including India and its north-eastern states. What is peculiar about CTVT is also that these “tumour or cancer cells” have nothing to do with cells of host (carrier) dog, but the cancer lineage continues to survive, thousands of years after the founder dog had long dead and gone.
CTVT in dogs – TVT is a common canine reproductive disease throughout the world. In dogs, TVT occurs between 1 and 7 years old (mean: 3 years old) with the lowest incidence above 10 years old. Some researchers reported higher prevalence in males, although others noted that more females were affected than the males. No sex predilection was detected in other reports. Higher incidence of TVT has also been found in crossbred/nondescript breed by some authors. TVT’s grow rapidly and more rapidly in neonatal and immune-suppressed dogs.
In the diseased or affected dogs, TVT appears as a cauliflower-like, pedunculated, nodular, papillary, or multi-lobulated in appearance ranging in size from a small nodule (5 mm) to a large mass. In real sense, finding a small nodule that bleeds and is located on the external genitalia is the most consistent symptom. In males, the cancerous lesions are mostly located on the more caudal part (bulbus glandis, 81.5%) and less often on the shaft (pars longa glandis, 25.9%) or the tip (9.9%) of the glans penis. In case of females, the lesion often begins in the dorsal wall of the vagina at the junction with the vestibule.
Sometimes, it bulges into the lumen of the vagina and can protrude through the vulva as an ulcerated, friable mass.
Additionally, when the TVT lesions are transplanted to adjacent skin and oral, nasal, or conjunctival mucosae, it may be manifested in several ways. There could be muzzle deformity, existence of friable fleshy cauliflower-like mass, halitosis, purulent nasal discharge and submandibular lymphadenopathy. Some of the affected dogs may also show signs of respiratory problem due to thickening of the soft tissues in the nares that result in upper airway obstruction, dyspnea, inability to swallow, anorexia and blood-tinged saliva are all attributed to the oral neoplasms.
Progressive extension of the tumorous mass on ocular tissues may cause hyperemia and conjunctivitis too. Metastasis is uncommon, however, when metastasis occurs, it is usually to the regional lymph nodes but kidney, spleen, eye, brain, pituitary and mesenteric lymph nodes may also be sites.
Diagnosis of TVT – the diagnosis is mainly based on the history, clinical signs, and cytologic examination of fine-needle aspirates or impression smears or by histopathologic evaluation of tissue biopsies. The diagnosis is not difficult as the clinical signs itself are self sufficient, however, it should be differentiated from other round cell tumors of the skin including histiocytoma, lymphoma, and mast cell tumor.
Treatment of TVT – although spontaneous regression can occur, TVTs are usually progressive and treated accordingly. Complete surgical excision, radiation therapy, and chemotherapy are effective treatments; however, chemotherapy is considered the treatment of choice.
Vincristine sulfate (0.5–0.7 mg/m2, IV, once weekly for 3–6 weeks) is reported to be effective. Adriamycin (30 mg/m2 for dogs weighing >10 kg; 1 mg/kg for dogs weighing ≤10 kg; IV, once every 3 weeks) and radiation therapy have been effective for those animals not responding to vincristine. It is mandatory to evaluate the animals under treatment and properly assessed the haematological and biochemical parameters before every shot and it should be done skillfully.
Public health issues – so far, there is no scientific report of transmission of TVT from affected animals to humans. However, the affected animals should be handled after taking considerable precautions like wearing a hand-gloves, mask and sanitizing the hands with proper antiseptic solutions.
Awareness or prevention – since the method of transmission is direct sexual contact, prevention of coitus or sexual contact is the best means of prevention. This also involves animal birth control (ABC) programme in a greater scale. Participation of public, education of the people, spreading awareness and reporting will help in controlling the spread of TVT.