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VACUNAS FELINAS ASOCIADAS A SARCOMAS (texto en inglés)

La comunidad veterinaria ha aceptado el hecho de que las vacunas inoculadas son causales del aumento de sarcomas de tejidos blandos identificados en gatos a finales de los años 90’. La gran pregunta a contestar es, cual es el mecanismo de la patogénesis de los sarcomas de los tejidos blandos en gatos. Las áreas más activas de desarrollo se ubican en el sitio de inoculación, donde se produce inflamación y una respuesta inmunitaria posterior a la administración de la vacuna

The veterinary community has now accepted the fact that vaccines played a causal role in the increase in the number of soft-tissue sarcomas identified in cats during the late 1990s. The bigger question to be answered is their exact mechanism in the pathogenesis of softtissue sarcomas in cats. The most active areas of research have focused on the role of injection-site inflammation and the immune response following vaccine administration. The literature is replete with evidence that consistently points to increased risk among cats receiving FeLV, rabies virus, and possibly other vaccine antigens.

The reported goal of a recent study, titled “Multicentric case-control study of risk factors associated with development of vaccine associated sarcomas in cats” ( JAVMA 233:1283–1292, 2003), was to examine the distribution of determinants of feline vaccine-associated sarcomas between groups of cats with various probabilities of having tumors caused by vaccines and potentially other injectables. Specifically, the investigation design was a prospective casecontrol study that determined if particular vaccine brand(s), other injectable medications, customary vaccination practices, or various host factors were associated with formation of vaccineassociated sarcomas in cats diagnosed between January 1, 1998 and June 15, 1999. Case material for this study came from veterinarians that submitted biopsy specimens from cats from the United States and Canada with confirmed diagnosis of soft-tissue sarcomas or basal cell carcinomas. The patients' medical histories were evaluated and a time window statistical analysis was used in conjunction with various assumptions about the case definitions.The authors concluded that no single vaccine brand or manufacturer within an antigen class was found to be associated with sarcoma formation. Other factors evaluated that were not found to be associated with sarcoma development were needle size, reused syringes, use of multi-dose vials, concomitant viral infections (FIP, FIV, FeLV), history of trauma, or residence.

Administration of cold vaccines and the use of two repositol medications (long-acting penicillin and methyl prednisolone acetate) were, however, found to be administered more frequently to cats that developed vaccineassociated sarcomas in control cats.

Although this study evaluated a variety of relative risks within antigen classes, it disappointingly failed to address the relative risk of sarcoma development between antigen classes (FeLV, rabies, and FVRCP). This study did not find differences of types of vaccines used within a vaccine antigen class. New less-inflammatory vaccines such as vectored recombinant vaccines did not reach the market until after the research began, thus the benefit of this new nonadjuvanted rabies vaccine could not be evaluated. The study did identify the use of two long-acting injectable medications other than vaccines with increased risk of injection-site tumor development. The medications linked were long-acting penicillin and methyl prednisolone acetate. These class products have been previously linked to injection-site sarcomas and are thought to produce chronic inflammation the injection site.1. The risk of use of “cold” vaccines was somewhat of a surprise, and although an interesting finding, needs to be verified by others. It is unlikely that the administration of a small volume (1 mL) of a liquid between 35° and 40° F in the subcutaneous tissue is in itself going to cause significant tissue damage or chromic inflammation at the vaccine administration site. This study, along with other studies, appears to refute the hypothesis that common chronic viral infections of cats with FIV and FeLV play a role in the pathogenesis of injection-site sarcomas.2, 3

As the search for a more specific role that vaccines play in the pathogenesis of these tumor proceeds, future epidemiologic studies should use more specific criteria for tumors caused by vaccines.

Although vaccine-associated sarcomas are tragic iatrogenic events, they fortunately occur in only between 1:1,000 to 1:10,000 vaccinates, which means differentiation between sarcomas that are non-vaccine related and those that are vaccine caused is often difficult. To merely include or exclude a tumor as vaccine caused based on injection-site location is a weakness of many past and current epidemiologic studies.

Although the current histologic criteria are helpful, histopathology is not an exact science; non-vaccines that induce tumors at vaccine sites may be evaluatedas being vaccine caused, and tumors that develop from vaccine material that is carried away from the vaccine site by macrophages may be considered ineligible for evaluation as being vaccine caused. More specific markers for vaccine-associated tumors, such as platelet-derived growth factor and other more specific markers, should be used in future studies.4, 5

The issue of vaccine-associated sarcomas is an important one, and this study, along with those done in the past, have helped us better understand this unfortunate iatrogenic event. It is clear, however, that more work needs to be done to further define the risk of routine vaccination of cats.

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Fuente: MERIAL