Resumen: Se presentó un perro, de raza mixta, no castrado, 15 años de edad, con hiporexia, constipación, letargia y dolor abdominal. En el examen físico, se identificó una masa intraabdominal. Las pruebas hematológicas evidenciaron anemia leve, normocítica y normocrómica y leucocitosis a causa de neutrofilia. Los resultados de bioquímica sérica mostraron alteraciones del nitrógeno ureico sanguíneo, fosfatasa alcalina sérica y creatinina. En el ultrasonido, se detectó un nódulo en bazo. Las radiografías evidenciaron un área radiopaca en abdomen, cerca de las vértebras lumbares. Se realizó laparotomía exploratoria y se encontró dos masas retroperitoneales. Se realizó la eutanasia del paciente, debido al difícil abordaje quirúrgico. El análisis histopatológico e inmunohistoquímico de las masas fue concluyente de un osteosarcoma extraesquelético. Los osteosarcomas extraesqueléticos son tumores malignos, de origen mesenquimal infrecuentes, sin involucramiento primario de tejido óseo o periostio. La localización retroperitoneal de estos tumores pocas veces ha sido reportada.Palabras clave: osteosarcoma extraesquelético, retroperitoneo, perro. Abstract:A 15-year-old not neutered mixed-breed dog was presented with hyporexia, constipation, lethargy and abdominal pain. An intra abdominal mass was identified during the physical examination. Mild normocytic and normochromic anemia and leukocytosis due to neutrophilia were detected in the complete blood count. Serum biochemistry results showed alterations in blood urea nitrogen, serum alkaline phosphatase, and creatinine. A splenic nodule was detected during the ultrasonographic examination, and radiographic findings showed a radiopaque area in the abdomen near the lumbar vertebrae. An exploratory laparotomy was done, and two retroperitoneal masses were found. Due to the difficult surgical approach euthanasia was elected. Histopathological and immunohistochemical evaluation of tissues was performed and the diagnosis of extraskeletal osteosarcoma was made. Extraskeletal osteosarcoma is an infrequent malign mesenchymal tumor without primary involvement of bone tissue or periosteum. Seldom has the retroperitoneal localization of this tumor been reported.

West Nile virus (WNV) and Saint Louis encephalitis virus (SLEV) share similar virus transmission cycles that involve birds as amplifiers and mosquitoes as vectors. Mammals, including humans, are dead-end-hosts that may be asymptomatic or develop more severe symptoms. Costa Rica is a hyperendemic country for several flaviviruses such as Dengue (DENV) and Zika (ZIKV) and previous research showed limited and restricted SLEV and WNV circulation in horses, sloths, and monkeys. Nevertheless, actual seroprevalence and high transmission areas are not yet identified. To determine putative WNV and SLEV circulation, we sampled peri-domestic and domestic animals, humans, wild birds, and mosquitoes in rural households located in two DENV and ZIKV hyperendemic regions during the rainy and dry seasons of 2017-2018 and conducted PRNT assays for serology and RT-PCR for virus detection. At Cuajiniquil, serological evidence of WNV and SLEV was found in equines, humans, chickens, and wild birds. Also, 5 seroconversion events were recorded for WNV (2 equine), SLEV (1 human), and DENV-1 (2 humans). At Talamanca, a lack of WNV circulation was found, but evidence of SLEV circulation was recorded in equines, humans, and wild birds. No evidence of active viral infection was found in any mosquitoes or wild bird samples. This seroconversion evidence supports the active and recent circulation of SLEV and WNV in these two regions. This study provides clear-cut evidence of WNV and SLEV circulation and should be considered by the health and epidemiology authorities for future prevention and differential diagnostics.

Resumen: Un equino, sin raza definida, hembra, de 6 años de edad, de San Rafael de Alajuela, presentaba disnea y descarga nasal bilateral de aspecto seroso y turbio, asociado a una masa irregular en el septo nasal que obstruía parcialmente las vías respiratorias superiores. Los hallazgos del cultivo, citología e histopatología determinaron que el agente causal de las lesiones era Conidiobolus coronatus. La conidiobolomicosis es una enfermedad subcutánea, piogranulomatosa, sin diseminación sistémica, que afecta la cavidad nasal en equinos. Posterior al debridamiento quirúrgico de la masa, el animal fue tratado con yoduro de sodio intravenoso, por varias semanas. Tres meses después de este procedimiento, no hubo recidiva de la lesión. Palabras clave:Conidiobolus coronatus, conidiobolomicosis, equino, rinitis piogranulomatosa. Abstract:A 6-year-old mixed breed female horse from San Rafael, Alajuela, Costa Rica was treated from bilateral turbid and serous nasal discharge related to an irregular mass in the nasal septum that was partially obstructing the upper respiratory tract. Findings related to the mycological culture, cytology and histopathology determined that Conidiobolus coronatus was the underlying infectious agent. Conidiobolomycosis is a pyogranulomatous subcutaneous disease, without systemic spread, that affects the nasal cavity in horses. After surgical debridement of the mass, the animal was treated with intravenous sodium iodide for several weeks. Three months after the procedure no recurrence of the lesion was detected.

During a routine check-up in a 6-year-old intact male Labrador Retriever and a 6-year-old intact male Boxer, a mass in their pelvic cavities was found. Both dogs were clinically healthy and did not display any clinical symptoms. The masses were surgically removed and sent to a pathology laboratory for analysis. The histopathological evaluation of both lesions diagnosis was: extraosseous aneurysmal bone cysts. This report describes the macroscopic and histopathological characteristics of the cysts in both patients.