Case report: Renal adenoma in a captive ocelot (Leopardus pardalis) in Costa Rica.

Reports of renal neoplasia are rare in neotropical wildcats. Ocelots (Leopardus pardalis) are medium-sized wildcats living in America's tropical forests. A 12-year-old captive ocelot was diagnosed with a renal mass occupying approximately 25% of the total right kidney volume. The tissue was stained with routine hematoxylin and eosin (H&E) and periodic acid-Schiff (PAS). Immunohistochemistry with the following markers was performed: cytokeratin (CK) AE1/AE3, CK19, CK 7, CD10, vimentin, Melan A, HMB45, Pax-8, and Wilms' tumor 1 (WT1). Histopathology revealed a well-differentiated epithelial tubular neoplasia with less than one mitotic figure per 2.37mm2 field. Vimentin and Pax-8 were the only positive markers. Immunohistochemically, neoplasia was diagnosed as a renal adenoma. Renal adenomas are seldom reported in neotropical wildcats. Reports on wild species are valuable for properly establishing a clinical prognosis for captive species. To the best of our knowledge, this is the first report that provides detailed microscopic and immunohistochemical descriptions of renal adenoma in a captive ocelot.

Molecular, morphological and histopathological evidence of Spirometra mansoni in wild and domestic animals from Costa Rica.

Spirometra mansoni is a diphyllobothroid cestode and one of the causing agents of sparganosis, a zoonotic foodborne and waterborne infection in humans. This parasite has an indirect life cycle with domestic and wild canids or felids as definitive hosts. The last report of S. mansoni in Costa Rica was done in 2004 by morphological assessment of worms, whereas molecular evidence of this species was obtained recently in the Americas. Herein, we present seven cases of spirometrosis in four dogs, three cats and a coyote from different regions of Costa Rica occurring in a time span of a year. Dog cases presented vomiting, hyporexia, lethargy and diarrhea, whereas cats were mostly asymptomatic. Moreover, the coyote was found with Spirometra sp. proglottids incidentally. Cytochrome oxidase subunit 1 (cox1) sequences of eggs or proglottids derived from all cases were analyzed with a Bayesian Inference phylogenetic tree and a haplotype network. These analyses showed the clustering of S. mansoni from Costa Rica with other sequences derived from Asia and America. Moreover, cox1 sequences clustered in two separate haplotypes, suggesting the high genetic diversity of the species. The present cases represent the first molecular evidence of the parasite in Central America; thus, extending its known range in the American continent.

Experimental infection of Artibeus lituratus bats and no detection of Zika virus in neotropical bats from French Guiana, Peru, and Costa Rica suggests a limited role of bats in Zika transmission.

Bats are important natural reservoir hosts of a diverse range of viruses that can be transmitted to humans and have been suggested to play an important role in the Zika virus (ZIKV) transmission cycle. However, the exact role of these animals as reservoirs for flaviviruses is still controversial. To further expand our understanding of the role of bats in the ZIKV transmission cycle in Latin America, we carried out an experimental infection in wild-caught Artibeus lituratus bats and sampled several free-living neotropical bats across three countries of the region. Experimental ZIKV infection was performed in wild-caught adult bats (4 females and 5 males). The most relevant findings were hemorrhages in the bladder, stomach and patagium. Significant histological findings included inflammatory infiltrate consisting of a predominance of neutrophils and lymphocytes, in addition to degeneration in the reproductive tract of males and females. This suggests that bat reproduction might be at some level affected by ZIKV. Leukopenia was also observed in some inoculated animals. Hemorrhages, genital alterations, and leukopenia are suggested to be caused by ZIKV; however, since these were wild-caught bats, we cannot exclude other agents. Detection of ZIKV by qPCR was observed at low concentrations in only two urine samples in two inoculated animals. All other animals and tissues tested were negative. Finally, no virus-neutralizing antibodies were found in any animal. To determine ZIKV infection in nature, the blood of a total of 2056 bats was sampled for ZIKV detection by qPCR. Most of the sampled individuals belonged to the genus Pteronotus sp. (23%), followed by the species Carollia sp. (17%), Anoura sp. (14%), and Molossus sp. (13.7%). No sample of any tested species was positive for ZIKV by qPCR. These results together suggest that bats are not efficient amplifiers or reservoirs of ZIKV and may not have an important role in ZIKV transmission dynamics.

Seasonal changes in the diversity, host preferences and infectivity of mosquitoes in two arbovirus-endemic regions of Costa Rica.

BACKGROUND: Mosquitoes are vectors of various arboviruses belonging to the genera Alphavirus and Flavivirus, and Costa Rica is endemic to several of them. The aim of this study was to describe and analyze the community structure of such vectors in Costa Rica. METHODS: Sampling was performed in two different coastal locations of Costa Rica with evidence of arboviral activity during rainy and dry seasons. Encephalitis vector surveillance traps, CDC female gravid traps and ovitraps were used. Detection of several arboviruses by Pan-Alpha and Pan-Flavi PCR was attempted. Blood meals were also identified. The Normalized Difference Vegetation Index (NDVI) was estimated for each area during the rainy and dry seasons. The Chao2 values for abundance and Shannon index for species diversity were also estimated. RESULTS: A total of 1802 adult mosquitoes belonging to 55 species were captured, among which Culex quinquefasciatus was the most caught species. The differences in NDVI were higher between seasons and between regions, yielding lower Chao-Sørensen similarity index values. Venezuelan equine encephalitis virus, West Nile virus and Madariaga virus were not detected at all, and dengue virus and Zika virus were detected in two separate Cx. quinquefasciatus specimens. The primary blood-meal sources were chickens (60%) and humans (27.5%). Both sampled areas were found to have different seasonal dynamics and population turnover, as reflected in the Chao2 species richness estimation values and Shannon diversity index. CONCLUSION: Seasonal patterns in mosquito community dynamics in coastal areas of Costa Rica have strong differences despite a geographical proximity. The NDVI influences mosquito diversity at the regional scale more than at the local scale. However, year-long continuous sampling is required to better understand local dynamics.

Parasitic fauna of bats from Costa Rica.

Bats are important reservoirs and spreaders of pathogens, including those of zoonotic concern. Though Costa Rica hosts one of the highest bat species' diversity, no information is available about their parasites. In order to investigate the occurrence of vector-borne pathogens (VBPs) and gastrointestinal (GI) parasites of chiropterans from this neotropical area, ectoparasites (n = 231) and stools (n = 64) were collected from 113 bats sampled in Santa Cruz (site 1) and Talamanca (site 2). Mites, fleas and ticks were morphologically and molecularly identified, as well as pathogens transmitted by vectors (VBPs, i.e., Borrelia spp., Rickettsia spp., Bartonella spp.) and from feces, such as Giardia spp., Cryptosporidium spp. and Eimeria spp. were molecularly investigated. Overall, 21 bat species belonging to 15 genera and 5 families were identified of which 42.5% were infested by ectoparasites, with a higher percentage of mites (38.9%, i.e., Cameronieta sp. and Mitonyssoides sp.) followed by flies (2.6%, i.e., Joblingia sp.) and tick larvae (1.7%, i.e., Ornithodoros sp.). Rickettsia spp. was identified in one immature tick and phylogenetically clustered with two Rickettsia species of the Spotted Fever Group (i.e., R. massiliae and R. rhipicephali). The frequency of GI parasite infection was 14%, being 3.1% of bats infected by Giardia spp. (un-identified non-duodenalis species), 1.5% by Eimeria spp. and 9.4% by Cryptosporidium spp. (bat and rodent genotypes; one C. parvum-related human genotype). The wide range of ectoparasites collected coupled with the detection of Rickettsia sp., Giardia and Cryptosporidium in bats from Costa Rica highlight the role these mammals may play as spreaders of pathogens and the need to further investigate the pathogenic potential of these parasites.

Boid Inclusion Body Disease Is Also a Disease of Wild Boa Constrictors.

Reptarenaviruses cause boid inclusion body disease (BIBD), a potentially fatal disease, occurring in captive constrictor snakes boas and pythons worldwide. Classical BIBD, characterized by the formation of pathognomonic cytoplasmic inclusion bodies (IBs), occurs mainly in boas, whereas in pythons, for example, reptarenavirus infection most often manifests as central nervous system signs with limited IB formation. The natural hosts of reptarenaviruses are unknown, although free-ranging/wild constrictor snakes are among the suspects. Here, we report BIBD with reptarenavirus infection in indigenous captive and wild boid snakes in Costa Rica using histology, immunohistology, transmission electron microscopy, and next-generation sequencing (NGS). The snakes studied represented diagnostic postmortem cases of captive and wild-caught snakes since 1989. The results from NGS on archival paraffin blocks confirm that reptarenaviruses were already present in wild boa constrictors in Costa Rica in the 1980s. Continuous sequences that were de novo assembled from the low-quality RNA obtained from paraffin-embedded tissue allowed the identification of a distinct pair of reptarenavirus S and L segments in all studied animals; in most cases, reference assembly could recover almost complete segments. Sampling of three prospective cases in 2018 allowed an examination of fresh blood or tissues and resulted in the identification of additional reptarenavirus segments and hartmanivirus coinfection. Our results show that BIBD is not only a disease of captive snakes but also occurs in indigenous wild constrictor snakes in Costa Rica, suggesting boa constrictors to play a role in natural reptarenavirus circulation. IMPORTANCE The literature describes cases of boid inclusion body disease (BIBD) in captive snakes since the 1970s, and in the 2010s, others and ourselves identified reptarenaviruses as the causative agent. BIBD affects captive snakes globally, but the origin and the natural host of reptarenaviruses remain unknown. In this report, we show BIBD and reptarenavirus infections in two native Costa Rican constrictor snake species, and by studying archival samples, we show that both the viruses and the disease have been present in free-ranging/wild snakes in Costa Rica at least since the 1980s. The diagnosis of BIBD in wild boa constrictors suggests that this species plays a role in the circulation of reptarenaviruses. Additional sample collection and analysis would help to clarify this role further and the possibility of, e.g., vector transmission from an arthropod host.

Passive epidemiological surveillance in wildlife in Costa Rica identifies pathogens of zoonotic and conservation importance.

Epidemiological surveillance systems for pathogens in wild species have been proposed as a preventive measure for epidemic events. These systems can minimize the detrimental effects of an outbreak, but most importantly, passive surveillance systems are the best adapted to countries with limited resources. Therefore, this research aimed to evaluate the technical and infrastructural feasibility of establishing this type of scheme in Costa Rica by implementing a pilot program targeting the detection of pathogens of zoonotic and conservation importance in wildlife. Between 2018 and 2020, 85 carcasses of free-ranging vertebrates were admitted for post-mortem and microbiology analysis. However, we encountered obstacles mainly related to the initial identification of cases and limited local logistics capacity. Nevertheless, this epidemiological surveillance scheme allowed us to estimate the general state of health of the country's wildlife by establishing the causes of death according to pathological findings. For instance, 60% (51/85) of the deaths were not directly associated with an infectious agent. Though in 37.6% (32/85) of these cases an infectious agent associated or not with disease was detected. In 27.1% (23/85) of the cases, death was directly related to infectious agents. Furthermore, 12.9% (11/85), the cause of death was not determined. Likewise, this wildlife health monitoring program allowed the detection of relevant pathogens such as Canine Distemper Virus, Klebsiella pneumoniae, Angiostrongylus spp., Baylisascaris spp., among others. Our research demonstrated that this passive surveillance scheme is cost-effective and feasible in countries with limited resources. This passive surveillance can be adapted to the infrastructure dedicated to monitoring diseases in productive animals according to the scope and objectives of monitoring wildlife specific to each region. The information generated from the experience of the initial establishment of a WHMP is critical to meeting the challenges involved in developing this type of scheme in regions with limited resources and established as hotspots for emerging infectious diseases.

Platelet depletion does not alter the course of Brucella abortus infection in vivo.

Brucellosis is a bacterial disease of animals and a zoonotic infection. Thrombocytopenia is a common outcome in long-lasting brucellosis in humans. Likewise, ex vivo experiments have shown that platelets may play a role in Brucella abortus infections. Following these reports, we explored the course of brucellosis in thrombocytopenic mice, using the non-toxic low-molecular-weight aspercetin protein that depletes platelets in vivo. Aspercetin does not induce systemic hemorrhage or inflammation, and when injected into mice, it generates a rapid dose-dependent drop in platelet counts without affecting central organs, disrupting hematological parameters, or the proinflammatory cytokine profile. Compared to the B. abortus infected control group, the infected thrombocytopenic mice did not show significant differences in the hematological profiles, pathological score, spleen, liver histopathology, or bacterial loads. Except for IL-6, which was higher in the infected thrombocytopenic mice, the TNF-α, IFN-γ and IL-10 did not significantly differ with the PBS-infected group. The results indicate that platelets do not play a significant role in modulating Brucella infection in vivo at the early stages of infection, which is commensurate with the stealthy strategy followed by Brucella organisms at the onset of the disease.

Serological Positivity against Selected Flaviviruses and Alphaviruses in Free-Ranging Bats and Birds from Costa Rica Evidence Exposure to Arboviruses Seldom Reported Locally in Humans.

Arboviruses have two ecological transmission cycles: sylvatic and urban. For some, the sylvatic cycle has not been thoroughly described in America. To study the role of wildlife in a putative sylvatic cycle, we sampled free-ranging bats and birds in two arbovirus endemic locations and analyzed them using molecular, serological, and histological methods. No current infection was detected, and no significant arbovirus-associated histological changes were observed. Neutralizing antibodies were detected against selected arboviruses. In bats, positivity in 34.95% for DENV-1, 16.26% for DENV-2, 5.69% for DENV-3, 4.87% for DENV-4, 2.43% for WNV, 4.87% for SLEV, 0.81% for YFV, 7.31% for EEEV, and 0.81% for VEEV was found. Antibodies against ZIKV were not detected. In birds, PRNT results were positive against WNV in 0.80%, SLEV in 5.64%, EEEV in 8.4%, and VEEV in 5.63%. An additional retrospective PRNT analysis was performed using bat samples from three additional DENV endemic sites resulting in a 3.27% prevalence for WNV and 1.63% for SLEV. Interestingly, one sample resulted unequivocally WNV positive confirmed by serum titration. These results suggest that free-ranging bats and birds are exposed to not currently reported hyperendemic-human infecting Flavivirus and Alphavirus; however, their role as reservoirs or hosts is still undetermined.

Serosurvey in Two Dengue Hyperendemic Areas of Costa Rica Evidence Active Circulation of WNV and SLEV in Peri-Domestic and Domestic Animals and in Humans.

Costa Rica harbors several flaviviruses, including Dengue (DENV), Zika (ZIKV), West Nile virus (WNV), and Saint Louis encephalitis virus (SLEV). While DENV and ZIKV are hyperendemic, previous research indicates restricted circulation of SLEV and WNV in animals. SLEV and WNV seroprevalence and high transmission areas have not yet been measured. To determine the extents of putative WNV and SLEV circulation, we sampled peri-domestic and domestic animals, humans, and mosquitoes in rural households located in two DENV and ZIKV hyperendemic regions during the rainy and dry seasons of 2017-2018 and conducted plaque reduction neutralization test assay for serology (PRNT) and RT-PCR for virus detection. In Cuajiniquil, serological evidence of WNV and SLEV was found in equines, humans, chickens, and wild birds. Additionally, five seroconversion events were recorded for WNV (2 equines), SLEV (1 human), and DENV-1 (2 humans). In Talamanca, WNV was not found, but serological evidence of SLEV circulation was recorded in equines, humans, and wild birds. Even though no active viral infection was detected, the seroconversion events recorded here indicate recent circulation of SLEV and WNV in these two regions. This study thus provides clear-cut evidence for WNV and SLEV presence in these areas, and therefore, they should be considered in arboviruses differential diagnostics and future infection prevention campaigns.

Esophageal spirocercosis with pulmonary egg deposition and secondary hypertrophic osteopathy in a dog from Costa Rica.

Spirocerca lupi is the etiologic agent of spirocercosis in canids from the tropical and subtropical regions of the world. A 1-year-old dog was presented with weight loss and diarrhea. Upon examination, thickened limbs, a mass in the lung's right middle lobe and an esophageal mass were found. The pulmonary mass aspirate revealed S. lupi eggs surrounded by a purulent infiltrate. Limb bone biopsies showed irregular mineralization and cartilaginous metaplasia. Treatment with doramectin resolved the initial clinical signs. However, regurgitation was reported 5 months later. Therefore, the dog received additional doramectin and later vomited a worm morphologically consistent with a S. lupi adult. Herein we report the esophageal migration of S. lupi with egg deposition to the lung parenchyma, accompanied by secondary hypertrophic osteopathy. This report highlights the presence of S. lupi in Costa Rica and the importance of including this parasite as a differential diagnosis when compatible signs are identified.

Cutaneous myofibroblastic fibrosarcoma in a margay (Leopardus wiedii): a case report

A routine check-up was performed on a captive 14-year-old female margay (Leopardus wiedii), a cutaneous mass was detected on the ventral thorax. The mass was surgically removed and sent for histopathological analysis. Histologically, the mass was a poorly-demarcated, highly cellular, infiltrative and unencapsulated mesenchymal neoplasm. Immunohistochemical labeling for smooth muscle actin and vimentin were positive, while desmin and cytokeratin were negative which is consistent with a myofibroblastic fibrosarcoma. This type of tumor has been diagnosed in wild felines, however this seems to be the first report of its occurrence in this L. wiedii. Wildlife oncology studies should be performed to promote our understanding of cancer in a species.

Cutaneous myofibroblastic fibrosarcoma in a margay (Leopardus wiedii): a case report

A routine check-up was performed on a captive 14-year-old female margay (Leopardus wiedii), a cutaneous mass was detected on the ventral thorax. The mass was surgically removed and sent for histopathological analysis. Histologically, the mass was a poorly-demarcated, highly cellular, infiltrative and unencapsulated mesenchymal neoplasm. Immunohistochemical labeling for smooth muscle actin and vimentin were positive, while desmin and cytokeratin were negative which is consistent with a myofibroblastic fibrosarcoma. This type of tumor has been diagnosed in wild felines, however this seems to be the first report of its occurrence in this L. wiedii. Wildlife oncology studies should be performed to promote our understanding of cancer in a species.(AU)

In vivo animal models confirm an increased virulence potential and pathogenicity of the NAP1/RT027/ST01 genotype within the Clostridium difficile MLST Clade 2.

BACKGROUND: Based on MLST analyses the global population of C. difficile is distributed in eight clades, of which Clade 2 includes the "hypervirulent" NAP1/RT027/ST01 strain along with various unexplored sequence types (STs). METHODS: To clarify whether this clinically relevant phenotype is a widespread feature of C. difficile Clade 2, we used the murine ileal loop model to compare the in vivo pro-inflammatory (TNF-α, IL-1ß, IL-6) and oxidative stress activities (MPO) of five Clade 2 clinical C. difficile isolates from sequence types (STs) 01, 41, 67, and 252. Besides, we infected Golden Syrian hamsters with spores from these strains to determine their lethality, and obtain a histological evaluation of tissue damage, WBC counts, and serum injury biomarkers (LDH, ALT, AST, albumin, BUN, creatinine, Na+, and Cl-). Genomic distances were calculated using Mash and FastANI to explore whether the responses were dictated by phylogeny. RESULTS: The ST01 isolate tested ranked first in all assays, as it induced the highest overall levels of pro-inflammatory cytokines, MPO activity, epithelial damage, biochemical markers, and mortality measured in both animal models. Statistically indistinguishable or rather similar outputs were obtained for a ST67 isolate in tests such as tissue damage, neutrophils count, and lethal activity. The results recorded for the two ST41 isolates tested were of intermediate magnitude and the ST252 isolate displayed the lowest pathogenic potential in all animal experiments. This ordering matched the genomic distance of the ST01 isolate to the non-ST01 isolates. CONCLUSIONS: Despite their close phylogenic relatedness, our results demonstrate differences in pathogenicity and virulence levels in Clade 2 C. difficile strains, confirm the high severity of infections caused by the NAP1/RT027/ST01 strain, and highlight the importance of C. difficile typing.

Neutrophils Dampen Adaptive Immunity in Brucellosis.

Brucella organisms are intracellular stealth pathogens of animals and humans. The bacteria overcome the assault of innate immunity at early stages of an infection. Removal of polymorphonuclear neutrophils (PMNs) at the onset of adaptive immunity against Brucella abortus favored bacterial elimination in mice. This was associated with higher levels of interferon gamma (IFN-γ) and a higher proportion of cells expressing interleukin 6 (IL-6) and inducible nitric oxide synthase (iNOS), compatible with M1 macrophages, in PMN-depleted B. abortus-infected (PMNd-Br) mice. At later times in the acute infection phase, the amounts of IFN-γ fell while IL-6, IL-10, and IL-12 became the predominant cytokines in PMNd-Br mice. IL-4, IL-1ß, and tumor necrosis factor alpha (TNF-α) remained at background levels at all times of the infection. Depletion of PMNs at the acute stages of infection promoted the premature resolution of spleen inflammation. The efficient removal of bacteria in the PMNd-Br mice was not due to an increase of antibodies, since the immunoglobulin isotype responses to Brucella antigens were dampened. Anti-Brucella antibodies abrogated the production of IL-6, IL-10, and IL-12 but did not affect the levels of IFN-γ at later stages of infection in PMNd-Br mice. These results demonstrate that PMNs have an active role in modulating the course of B. abortus infection after the adaptive immune response has already developed.

Extraosseous aneurysmal bone cyst in dogs: a report of two cases

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.

Extraosseous aneurysmal bone cyst in dogs: a report of two cases

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.(AU)

Depletion of Complement Enhances the Clearance of Brucella abortus in Mice.

Brucellosis is a bacterial disease of animals and humans. Brucella abortus barely activates the innate immune system at the onset of infection, and this bacterium is resistant to the microbicidal action of complement. Since complement stands as the first line of defense during bacterial invasions, we explored the role of complement in B. abortus infections. Brucella abortus-infected mice depleted of complement with cobra venom factor (CVF) showed the same survival rate as mice in the control group. The complement-depleted mice readily eliminated B. abortus from the spleen and did so more efficiently than the infected controls after 7 days of infection. The levels of the proinflammatory cytokines tumor necrosis factor alpha and interleukin-6 (IL-6) remained within background levels in complement-depleted B. abortus-infected mice. In contrast, the levels of the immune activator cytokine gamma interferon and the regulatory cytokine IL-10 were significantly increased. No significant histopathological changes in the liver and spleen were observed between the complement-depleted B. abortus-infected mice and the corresponding controls. The action exerted by Brucella on the immune system in the absence of complement may correspond to a broader phenomenon that involves several components of innate immunity.

Persistence of Brucella abortus in the Bone Marrow of Infected Mice.

Brucellosis is a zoonotic bacterial infection that may persist for long periods causing relapses in antibiotic-treated patients. The ability of Brucella to develop chronic infections is linked to their capacity to invade and replicate within the mononuclear phagocyte system, including the bone marrow (BM). Persistence of Brucella in the BM has been associated with hematological complications such as neutropenia, thrombocytopenia, anemia, and pancytopenia in human patients. In the mouse model, we observed that the number of Brucella abortus in the BM remained constant for up to 168 days of postinfection. This persistence was associated with histopathological changes, accompanied by augmented numbers of BM myeloid GMP progenitors, PMNs, and CD4+ lymphocytes during the acute phase (eight days) of the infection in the BM. Monocytes, PMNs, and GMP cells were identified as the cells harboring Brucella in the BM. We propose that the BM is an essential niche for the bacterium to establish long-lasting infections and that infected PMNs may serve as vehicles for dispersion of Brucella organisms, following the Trojan horse hypothesis. Monocytes are solid candidates for Brucella reservoirs in the BM.

Neotropical bats that co-habit with humans function as dead-end hosts for dengue virus.

Several studies have shown Dengue Virus (DENV) nucleic acids and/or antibodies present in Neotropical wildlife including bats, suggesting that some bat species may be susceptible to DENV infection. Here we aim to elucidate the role of house-roosting bats in the DENV transmission cycle. Bats were sampled in households located in high and low dengue incidence regions during rainy and dry seasons in Costa Rica. We captured 318 bats from 12 different species in 29 households. Necropsies were performed in 205 bats to analyze virus presence in heart, lung, spleen, liver, intestine, kidney, and brain tissue. Histopathology studies from all organs showed no significant findings of disease or infection. Sera were analyzed by PRNT90 for a seroprevalence of 21.2% (51/241), and by PCR for 8.8% (28/318) positive bats for DENV RNA. From these 28 bats, 11 intestine samples were analyzed by RT-PCR. Two intestines were DENV RNA positive for the same dengue serotype detected in blood. Viral isolation from all positive organs or blood was unsuccessful. Additionally, viral load analyses in positive blood samples by qRT-PCR showed virus concentrations under the minimal dose required for mosquito infection. Simultaneously, 651 mosquitoes were collected using EVS-CO2 traps and analyzed for DENV and feeding preferences (bat cytochrome b). Only three mosquitoes were found DENV positive and none was positive for bat cytochrome b. Our results suggest an accidental presence of DENV in bats probably caused from oral ingestion of infected mosquitoes. Phylogenetic analyses suggest also a spillover event from humans to bats. Therefore, we conclude that bats in these urban environments do not sustain DENV amplification, they do not have a role as reservoirs, but function as epidemiological dead end hosts for this virus.