Deterioration and Metastasis of a Canine Transmissible Venereal Tumor in a Dog Associated with a CPV-2

Abstract

Virus infection has been documented to be associated with tumor progression. A 2- year-old female beagle was inoculated in the dorsal flank with viable canine transmissible venereal tumor (CTVT) cells for routine laboratory tumor passage. Tumor masses were palpable 2 weeks after inoculation, then grew progressively, and the tumor size remained stable. Parvovirus (CPV-2) infection was diagnosed by RT-PCR at week 11 after tumor inoculation and, 2 weeks later, the primary tumors began to grow again. Besides, palpable tumor masses were found scattered around the primary tumor sites. Because of the deteriorating condition of the animal and the dramatic increase in tumor size and number, the dog was euthanized and venous blood collected for a complete blood count and serum chemistry analysis. Postmortem examination revealed a disseminated CTVT involving the subcutaneous tissue, spleen, liver, lung, and multiple lymph nodes, which was confirmed by histopathological examination and the presence of LINE gene insertion in the 5 end of c-myc gene, a characteristic of CTVT cells, shown using RT-PCR. Lymphoid cell depletion in the spleen and lymph nodes, and focal micro-necrosis of the cryptic epithelium of the small intestine were also seen. Blood analysis showed decreased levels of albumin and total blood protein and an extremely low lymphocyte count. Here, we report a rare case in which a stable CTVT became a devastating metastatic CTVT after a CPV-2 infection. The immunosuppressive effects of CPV-2 might account for the breakdown in the symbiotic balance between the CTVT and host that caused the stable tumor to develop into a metastatic cancer. The correlation between parvovirus infection and aggravated CTVT progression is worthy of further investigation.