Transmissible Venereal Tumors in Dogs

Not all tumors in dogs are cancerous and this applies to canine transmissible venereal tumors. However, it is possible that cancer will develop. Transmissible cancers are those which can be passed on from one host to another. They are incredibly rare in all mammals^[1], including humans, but TVT in dogs is one of the most unfortunate exceptions.

This type of tumor in dogs appears on the genitals of both male and female dogs. In the male it can appear on the penis and prepuce (foreskin) and usually on the vulva of females. It is possible to find it on other parts of the body such as the perineum, face, mouth, nose, tongue, eyes or the legs. However, presenting on these areas is rare. This type of tumor is a neoplasm meaning it is a tumor of abnormally excessive growth. Fortunately, it is overall relatively rare, but a veterinary specialist is needed to achieve diagnosis.

The most common form of transmission of this tumor is through sexual intercourse. For this reason, it is most common in stray unneutered dogs as they roam and freely and actively seek mates. Tropical and subtropical climates are areas of greater risk. The affected cells are what pass on the disease, so it is possible for the host dog to not have an active tumor and yet still pass it on to a mate.

Small lesions on mucus membranes of the penis or vagina usually act as a gateway for tumor cells. The infectious nature means it is possible to be passed through smelling or licking of an infected area, a common practice of dogs.

Stages of canine transmissible venereal tumors:

In only about 5% of cases does the cancer ulcerate or metastasize and lead to symptoms^[2]. The evolution of the tumor starts with transmission which will be asymptomatic to begin with. The stages of TVT are:

1. Transplantation (usually through sexual intercourse or other close contact).
2. Progressive growth over 5 to 7 weeks.
3. After 3 to 9 weeks the immune system is usually able to reject the TVT. This is known as the regression stage and is spontaneous if treatment has not been applied.
4. If the immune system is unable to reject it, the cancer ulcerates or metastasizes.

Due to the importance of a strong immune system, the likelihood of contracting this infection is greater in dogs which have a compromised immune system. This could be due to stress, starvation or a preexisting pathological condition. These are further reasons stray dogs are more likely to develop this type of tumor.

Are canine transmissible venereal tumors contagious to humans?

A zoonotic disease is one which can be passed from an animal species on to humans. Rabies is a good example and is well known for being contagious to humans. Fortunately, TVT is not one of them and is not contagious to most species. However, it is possible it can be transferred to other canid species such as foxes and wolves.

Imagen: http://www.smallanimaltalk.com/

We might suspect the presence of a canine venereal tumor if we see the presence of lesions or inflammation on the penis or vagina. While tumors can grow on the prepuce and shaft of the penis, they can also present on the base of the penis making them harder to see at the beginning. The tumors present in cauliflower shaped protrusions or modules which seem to have a stem. They can ulcerate and occur as either solitary or multiple tumors. The dog may lick their private area if they feel

Other symptoms of transmissible venereal tumor include discharge from the genitals and bleeding. However, it is not generally associated with hematuria which presents itself as the appearance of blood in the urine. The bleeding would otherwise be from the tumor site itself. However, as the tumor grows it can put pressure on the urethra and cause obstruction leading to difficulty in urination. In female dogs, the presence of bleeding from the vulva can be confused with the estrus period. If we see that the dog bleeds for longer than usual, then it is advisable to take them to the veterinarian.

Although rare, it is possible to have tumor growth on the face. If this is the case, then the tumors may present there. If they occur in the nasal passage then you may see mucous discharge or nosebleeds. Facial swelling will also likely present.

As you can see, the picture above shows an advanced case of transmisible venereal tumors in dogs. However, if the tumor gets to this point, then it is usually because intervention was not taken soon enough. There are many different types of cancer which affect dogs, so it does not necessarily mean that visible growth will be TVT. The veterinarian will need to perform different tests. Radiographic assessment in the form of an X-ray may be taken to see the extent of the tumor growth.

A complete blood count (CBC) will also be taken to determine white blood cell levels and other assessments. Urine samples will also be taken for urinalysis. However, a cytological assessment will be needed, so a biopsy will be performed to confirm if the tumor is cancerous.

If the tumor does metastasize and generate cancer, the result will be a lower intensity cancer than others. For this reason, it generally responds well to treatment. This treatment will usually be in the form of chemotherapy which is preferred to surgical intervention. Surgery in the area is delicate and can cause further problems. Chemotherapy drugs such as vincristine and interleukin-2 are described in a 2015 study as having “impressive therapeutic results”^[3].

Radiotherapy may also be implemented. With chemotherapy, sessions usually last between 3 and 6 weeks. With radiotherapy, it is possible the treatment may be effective after one session. However, we should be considerate of the side effects of these harsh cancer therapies. Complications such as bone marrow suppression may occur^[4]. Control analysis will need to be carried out to ensure treatment of these complications occurs. Due to the successful history of treatment for TVT, life expectancy shouldn't be drastically compromised if remission doesn't occur.

As we state above, sterilization of the animal is advised as the most effective preventative action for TVT. It is difficult to control sexual activity in unneutered dogs, especially when out in public with other dogs present. Vaccines are used to treat many types of canine disease and there is research to suggest that dendritic cell based vaccines may be useful in combating these types of cancer transmission^[5]. However, it would not be a core-vaccine due to the relative infrequency of the disease. It would also depend on the rates of transmission in the country or region. Dogs that live in shelters and abandoned or stray dogs will need particular prevention methods due to the accessibility of potential sexual partners.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Transmissible Venereal Tumors in Dogs, we recommend you visit our Other health problems category.