Reemergence of Sylvatic Dengue Virus Serotype 2 in Kedougou, Senegal, 2020.

In 2020, a sylvatic dengue virus serotype 2 infection outbreak resulted in 59 confirmed dengue cases in Kedougou, Senegal, suggesting those strains might not require adaptation to reemerge into urban transmission cycles. Large-scale genomic surveillance and updated molecular diagnostic tools are needed to effectively prevent dengue virus infections in Senegal.

Evidence of Australian wild deer exposure to N. caninum infection and potential implications for the maintenance of N. caninum sylvatic cycle.

Infections with the coccidian parasite Neospora caninum affect domestic and wild animals worldwide. In Australia, N. caninum infections cause considerable losses to the cattle industry with seroprevalence of 8.7% in beef and 10.9% in dairy cattle. Conversely, the role of wild animals, in maintaining the parasite cycle is also unclear. It is possible that native or introduced herbivorous species could be reservoir hosts of N. caninum in Australia, but to date, this has not been investigated. We report here the first large-scale screening of N. caninum antibodies in Australian wild deer, spanning three species (fallow, red and sambar deer). Consequently, we also assessed two commercial cELISA tests validated for detecting N. caninum in cattle for their ability to detect N. caninum antibodies in serum samples of wild deer. N. caninum antibodies were detected in 3.7% (7/189, 95% CI 1.8 - 7.45) of the wild deer serum samples collected in south-eastern Australia (n = 189), including 97 fallow deer (Dama dama), 14 red deer (Cervus elaphus), and 78 sambar deer (Rusa unicolor). Overall, our study provides the first detection of N. caninum antibodies in wild deer and quantifies deer's potential role in the sylvatic cycle of N. caninum.

Wild mammals involved in the transmission of Trypanosoma cruzi and food sources of Triatoma sherlocki in an endemic region of northeastern Brazil.

The present study, carried out in the municipality of Gentio do Ouro, Bahia, Brazil aimed to evaluate which wild mammals may be involved in the transmission of T. cruzi and which are the blood sources for triatomines collected in the study area. PCR analysis of 31 wild mammals captured revealed T. cruzi infection in 6.4% (2/31): one specimen of the opossum Didelphis albiventris (1/3) and one of the rodent Kerodon rupestris (1/5); despite being more frequent in the area, no specimen of the rodent Thrichomys sp. (0/23) was infected. A total of 169 triatomines were captured. The conclusive detection of food sources was possible only for Triatoma sherlocki Papa et al., 2002 (n = 56), with evidence for: K. rupestris (35.7%), Gallus (17.9%), D. albiventris (14.3%), Homo sapiens (14.3%), Tropidurus hispidus (7.1%), Leopardus geoffroyi (5.3%), Conepatus semistriatus (1.8%), Thrichomys inermis (1.8%) and Rattus norvegicus (1.8%). Triatomines of the species T. sherlocki showed food eclecticism, including feeding on humans, with some of them being captured at dwellings. These facts make this triatomine a potential link for the transmission of T. cruzi between wild and anthropic environments, highlighting a latent risk of the reemergence of Chagas disease outbreaks.

Experimental SARS-CoV-2 Infection of Bank Voles.

After experimental inoculation, severe acute respiratory syndrome coronavirus 2 infection was confirmed in bank voles by seroconversion within 8 days and detection of viral RNA in nasal tissue for up to 21 days. However, transmission to contact animals was not detected. Thus, bank voles are unlikely to establish effective transmission cycles in nature.

Capybara and Brush Cutter Involvement in Q Fever Outbreak in Remote Area of Amazon Rain Forest, French Guiana, 2014.

We investigated a Q fever outbreak that occurred in an isolated area of the Amazon Rain Forest in French Guiana in 2014. Capybara fecal samples were positive for Coxiella burnetii DNA. Being near brush cutters in use was associated with disease development. Capybaras are a putative reservoir for C. burnetii.

Little Evidence of Zika Virus Infection in Wild Long-Tailed Macaques, Peninsular Malaysia.

We tested a sample of 234 wild long-tailed macaques (Macaca fascicularis) trapped in Peninsular Malaysia in 2009, 2010, and 2016 for Zika virus RNA and antibodies. None were positive for RNA, and only 1.3% were seropositive for neutralizing antibodies. Long-tailed macaques are unlikely to be reservoirs for Zika virus in Malaysia.

Aedes vector-host olfactory interactions in sylvatic and domestic dengue transmission environments.

Interactions between Aedes (Stegomyia) species and non-human primate (NHP) and human hosts govern the transmission of the pathogens, dengue, zika, yellow fever and chikungunya viruses. Little is known about Aedes mosquito olfactory interactions with these hosts in the domestic and sylvatic cycles where these viruses circulate. Here, we explore how the different host-derived skin odours influence Aedes mosquito responses in these two environments. In field assays, we show that the cyclic ketone cyclohexanone is a signature cue for Aedes mosquitoes to detect the NHP baboon, sykes and vervet, whereas for humans, it is the unsaturated aliphatic keto-analogue 6-methyl-5-hepten-2-one (sulcatone). We find that in the sylvatic environment, CO2-baited traps combined with either cyclohexanone or sulcatone increased trap catches of Aedes mosquitoes compared to traps either baited with CO2 alone or CO2 combined with NHP- or human-derived crude skin odours. In the domestic environment, each of these odourants and crude human skin odours increased Aedes aegypti catches in CO2-baited traps. These results expand our knowledge on the role of host odours in the ecologies of Aedes mosquitoes, and the likelihood of associated spread of pathogens between primates and humans. Both cyclohexanone and sulcatone have potential practical applications as lures for monitoring Aedes disease vectors.

Trichinella spp. in wild mesocarnivores in an endemic setting.

Human trichinellosis and Trichinella infection in pigs are both still endemic in the Balkans, including Serbia. Because of the flow between the sylvatic and the domestic cycle of Trichinella spp., monitoring wildlife has been recommended for the risk assessment of Trichinella spp. infection in swine. We have previously shown the presence of Trichinella infection in wild carnivores including the wolf and the golden jackal, and here we report on Trichinella infection in several other mesocarnivore species. From a total of 469 animals collected between 1994 and 2013, Trichinella larvae were detected in 29 (6.2%, 95% CI = 4.0-8.4) animals, including 14 red foxes (4.7%), 7 wild cats (35%), 5 beech martens (4.8%), 2 pine martens (16.7%), and 1 European badger (6.25%). No Trichinella larvae were detected in the examined specimens of European polecats, steppe polecats and European otters. Species identification of the Trichinella larvae performed for 18 positive samples revealed T. spiralis in 77.8% and T. britovi in 22.2% of the isolates. Both species were detected in red foxes and wild cats. The predominance of T. spiralis in wildlife in Serbia indicates the (past or present) spillover of this pathogen from domestic to wild animals.

Identification of Wild Boar-Habitat Epidemiologic Cycle in African Swine Fever Epizootic.

The African swine fever epizootic in central and eastern European Union member states has a newly identified component involving virus transmission by wild boar and virus survival in the environment. Insights led to an update of the 3 accepted African swine fever transmission models to include a fourth cycle: wild boar-habitat.

Climate change impacts on the conservation outlook of populations on the poleward periphery of species ranges: A case study of Canadian black-tailed prairie dogs (Cynomys ludovicianus).

Given climate change, species' climatically suitable habitats are increasingly expected to shift poleward. Some imperilled populations towards the poleward edge of their species' range might therefore conceivably benefit from climate change. Interactions between climate and population dynamics may be complex, however, with climate exerting effects both indirectly via influence over food availability and more directly, via effects on physiology and its implications for survival and reproduction. A thorough understanding of these interactions is critical for effective conservation management. We therefore examine the relationship between climate, survival and reproduction in Canadian black-tailed prairie dogs, a threatened keystone species in an imperilled ecosystem at the northern edge of the species' range. Our analyses considered 8 years of annual mark-recapture data (2007-2014) in relation to growing degree days, precipitation, drought status and winter severity, as well as year, sex, age and body mass. Survival was strongly influenced by the interaction of drought and body mass class, and winter temperature severity. Female reproductive status was associated with the interaction of growing degree days and growing season precipitation, with spring precipitation and with winter temperature severity. Results related to body mass suggested that climatic variables exerted their effects via regulation of food availability with potential linked effects of food quality, immunological and behavioural implications, and predation risk. Predictions of future increases in drought conditions in North America's grassland ecosystems have raised concerns for the outlook of Canadian black-tailed prairie dogs. Insights gained from the analyses, however, point to mitigating species management options targeted at decoupling the mechanisms by which climate exerts its negative influence. Our approach highlights the importance of understanding the interaction between climate and population dynamics in peripheral populations whose viability might ultimately determine their species' ability to track climatically suitable space.

Maintenance of rabies-free areas.

Rabies is endemic in many parts of the world and is maintained in particular host species. Surveillance activities in areas that have remained rabies free or that have succeeded in eliminating the rabies virus (RABV) must continue, so as to effectively detect any infected animals in a timely manner. Rabies should be classified as a notifiable disease both in animals and in humans, irrespective of the rabies status of the country, and the establishment of a legal framework for biting animals is of the utmost importance. The maintenance of rabies-free status depends, in part, on the geographical situation of a country. A wide range of measures have proven effective, such as the maintenance of the mass vaccination of dogs, the establishment of cordons sanitaires to prevent the reincursion of sylvatic (wildlife) rabies, the application of human prophylaxis, the implementation of strict measures for travelling with companion animals (mainly domestic dogs and cats) and risk-based surveillance. Awareness regarding rabies among personnel working at border entry points as well as among the general public, veterinarians and general practitioners is also a major factor in ensuring the effectiveness of the surveillance network. Cross-border threats, even for islands, strengthen the need for regional cooperation, irrespective of the rabies status of the countries involved. Another important measure is the maintenance of adequate laboratory capacity for rapid and reliable diagnosis.

La rage est endémique dans de nombreuses régions du monde où certaines espèces hôtes assurent la persistance du virus. Les activités de surveillance doivent être poursuivies dans les zones demeurées indemnes de rage ou qui ont réussi à éliminer le virus rabique afin de pouvoir détecter rapidement tout animal infecté. La rage doit être inscrite sur la liste des maladies humaines et animales à déclaration obligatoire, indépendamment du statut du pays à l'égard de la rage ; de même, il est absolument primordial de mettre en place une réglementation sur les animaux mordeurs. Le maintien du statut indemne de rage dépend en partie de la situation géographique du pays. Un large éventail de mesures ont fait preuve de leur efficacité, notamment la vaccination massive et continue des chiens, la mise en place de cordons sanitaires afin d'empêcher toute nouvelle incursion de la rage sylvatique (affectant la faune sauvage), le recours à la prophylaxie chez l'homme, la mise en oeuvre d'une réglementation rigoureuse sur les voyages avec des animaux de compagnie (chiens et chats principalement) et la surveillance basée sur le risque. La sensibilisation des personnels chargés des contrôles aux frontières, du grand public, des vétérinaires et des médecins généralistes au problème de la rage est également un facteur crucial pour garantir l'efficacité du réseau de surveillance. Les menaces transfrontalières (même dans un contexte insulaire) renforcent l'impératif d'une coopération régionale quel que soit le statut des pays participants au regard de la rage. Une autre mesure importante est de s'assurer que les laboratoires sont dotés des capacités appropriées pour réaliser un diagnostic rapide et fiable.

La rabia, enfermedad endémica en muchas partes del mundo, se perpetúa en determinadas especies que ejercen de anfitrión. Es imperativo que en aquellas zonas que se han mantenido libres de rabia o donde se ha logrado eliminar el virus rábico se sigan efectuando labores de vigilancia, a fin de detectar eficazmente y con prontitud la presencia de todo animal infectado. La rabia debe ser considerada enfermedad de declaración obligatoria tanto en animales como en personas, independientemente del estatuto del país con respecto a la enfermedad. En este sentido, es de la mayor importancia instituir un ordenamiento jurídico aplicable a los animales mordedores. El mantenimiento del estatuto de «libre de rabia¼ depende en parte de la situación geográfica de cada país. Hay toda una panoplia de medidas probadamente eficaces, como el mantenimiento de la vacunación masiva de perros, la creación de cordones sanitarios para impedir toda nueva incursión de rabia selvática (en la fauna silvestre), la administración de profilaxis a las personas, la aplicación de estrictas medidas de control de los viajes con animales de compañía (principalmente perros y gatos domésticos) y la vigilancia basada en el riesgo. La sensibilización acerca de la rabia del personal empleado en puntos de entrada fronterizos, así como del gran público, los veterinarios y el personal médico en general también es un factor básico para que la red de vigilancia sea eficaz. Las amenazas transfronterizas, incluso en territorios insulares, hacen tanto más necesaria la cooperación regional, sea cual sea el estatuto con respecto a la rabia de los países en cuestión. Otra medida importante consiste en mantener una adecuada capacidad de laboratorio para efectuar diagnósticos rápidos y fiables.

Rabies in dogs, livestock and wildlife: a veterinary perspective.

While major progress has been made in the control of rabies in the Western Hemisphere, large parts of Europe and some parts of Asia, the disease continues to kill tens of thousands of people every year. Its highest burden is in resourcelimited countries in Asia and Africa, disproportionately affecting children and poor rural communities. Today, domesticated dogs are responsible for the vast majority of human rabies cases. In late 2015, rabies experts from around the world gathered at the Rabies Global Conference in Geneva, Switzerland, and launched the ambitious initiative to end deaths from dog-mediated human rabies by 2030. The most cost-effective and sustainable approach to achieve this goal is to eliminate the disease at source through mass dog vaccination. In this article, the role of and challenges faced by Veterinary Services in resourcelimited settings in implementing the dog vaccination strategy to reduce the human rabies burden are discussed, together with the role of wildlife in disease control and why the 'One Health' approach is indispensable on the path towards a dograbies- free future.

Malgré les progrès considérables accomplis en matière de lutte contre la rage dans l'hémisphère occidental, dans une grande partie de l'Europe et en certains endroits d'Asie, la maladie continue à faire plusieurs dizaines de milliers de victimes chaque année dans le monde. Ce sont les pays à faibles ressources d'Asie et d'Afrique qui sont les plus touchés, avec une majorité écrasante de victimes parmi les enfants et dans les communautés rurales pauvres. Aujourd'hui, les chiens domestiques sont de loin la principale cause des cas de rage humaine. En décembre 2015, des experts du monde entier réunis à Genève (Suisse) à l'occasion de la Conférence mondiale sur la rage intitulée « Élimination mondiale de la rage humaine transmise par les chiens : agissons maintenant ! ¼ ont lancé une initiative ambitieuse visant à mettre fin aux décès humains dus à la rage transmise par les chiens d'ici 2030. La méthode la plus efficace et durable pour atteindre cet objectif consiste à éliminer la maladie à sa source au moyen de la vaccination massive des chiens. Les auteurs examinent le rôle des Services vétérinaires et les difficultés auxquelles ceux-ci sont confrontés lorsqu'ils entreprennent d'appliquer une stratégie de vaccination des chiens destinée à réduire le fardeau de la rage humaine dans un contexte de ressources limitées. Ils évoquent également l'importance de prendre en compte la faune sauvage dans le cadre du contrôle de la rage et expliquent en quoi l'approche « Une seule santé ¼ est incontournable pour avancer vers l'objectif d'un monde indemne de rage canine.

Aunque la lucha antirrábica ha conocido avances muy sustanciales en el hemisferio occidental, grandes partes de Europa y ciertas zonas de Asia, la enfermedad sigue matando a decenas de miles de personas al año. La carga más elevada de rabia se da en países con escasos recursos de Asia y África, donde la enfermedad afecta desproporcionadamente a los niños y a las comunidades rurales pobres. A día de hoy, los perros domésticos son responsables de la inmensa mayoría de los casos de rabia humana. A finales de 2015, especialistas del mundo entero se dieron cita en Ginebra (Suiza) para celebrar la conferencia mundial titulada «Eliminación mundial de la rabia humana transmitida por perros. ¡Actuemos ahora!¼ y poner en marcha la ambiciosa iniciativa de acabar con las muertes por rabia transmitida por perros como muy tarde en 2030. Para cumplir este objetivo, el método más sostenible y más eficaz en relación con el costo consiste en eliminar la enfermedad en su foco de origen, procediendo para ello a vacunaciones masivas de perros. Los autores exponen la función de los Servicios Veterinarios y las dificultades que afrontan en situaciones de escasez de recursos a la hora de aplicar la estrategia de vacunación canina para reducir la carga de rabia humana, así como el papel de la fauna silvestre en el control de la enfermedad y la razón por la cual es indispensable aplicar los planteamientos de «Una sola salud¼ para avanzar hacia un futuro libre de rabia.

Highly Divergent Dengue Virus Type 2 in Traveler Returning from Borneo to Australia.

Dengue virus type 2 was isolated from a tourist who returned from Borneo to Australia. Phylogenetic analysis identified this virus as highly divergent and occupying a basal phylogenetic position relative to all known human and sylvatic dengue virus type 2 strains and the most divergent lineage not assigned to a new serotype.

Diversity, host switching and evolution of Plasmodium vivax infecting African great apes.

Plasmodium vivax is considered to be absent from Central and West Africa because of the protective effect of Duffy negativity. However, there are reports of persons returning from these areas infected with this parasite and observations suggesting the existence of transmission. Among the possible explanations for this apparent paradox, the existence of a zoonotic reservoir has been proposed. May great apes be this reservoir? We analyze the mitochondrial and nuclear genetic diversity of P. vivax parasites isolated from great apes in Africa and compare it to parasites isolated from travelers returning from these regions of Africa, as well as to human isolates distributed all over the world. We show that the P. vivax sequences from parasites of great apes form a clade genetically distinct from the parasites circulating in humans. We show that this clade's parasites can be infectious to humans by describing the case of a traveler returning from the Central African Republic infected with one of them. The relationship between this P. vivax clade in great apes and the human isolates is discussed.

Ecological host fitting of Trypanosoma cruzi TcI in Bolivia: mosaic population structure, hybridization and a role for humans in Andean parasite dispersal.

An improved understanding of how a parasite species exploits its genetic repertoire to colonize novel hosts and environmental niches is crucial to establish the epidemiological risk associated with emergent pathogenic genotypes. Trypanosoma cruzi, a genetically heterogeneous, multi-host zoonosis, provides an ideal system to examine the sylvatic diversification of parasitic protozoa. In Bolivia, T. cruzi I, the oldest and most widespread genetic lineage, is pervasive across a range of ecological clines. High-resolution nuclear (26 loci) and mitochondrial (10 loci) genotyping of 199 contemporaneous sylvatic TcI clones was undertaken to provide insights into the biogeographical basis of T. cruzi evolution. Three distinct sylvatic parasite transmission cycles were identified: one highland population among terrestrial rodent and triatomine species, composed of genetically homogenous strains (Ar = 2.95; PA/L = 0.61; DAS = 0.151), and two highly diverse, parasite assemblages circulating among predominantly arboreal mammals and vectors in the lowlands (Ar = 3.40 and 3.93; PA/L = 1.12 and 0.60; DAS = 0.425 and 0.311, respectively). Very limited gene flow between neighbouring terrestrial highland and arboreal lowland areas (distance ~220 km; FST = 0.42 and 0.35) but strong connectivity between ecologically similar but geographically disparate terrestrial highland ecotopes (distance >465 km; FST = 0.016-0.084) strongly supports ecological host fitting as the predominant mechanism of parasite diversification. Dissimilar heterozygosity estimates (excess in highlands, deficit in lowlands) and mitochondrial introgression among lowland strains may indicate fundamental differences in mating strategies between populations. Finally, accelerated parasite dissemination between densely populated, highland areas, compared to uninhabited lowland foci, likely reflects passive, long-range anthroponotic dispersal. The impact of humans on the risk of epizootic Chagas disease transmission in Bolivia is discussed.

Sylvatic Infestation of Oklahoma Reptiles with Immature Ixodes scapularis (Acari: Ixodidae).

Reptiles were collected in nine counties in Oklahoma from September 2002 to May 2004 and examined for Ixodes scapularis (Say) larvae and nymphs to determine seasonal incidence and prevalence of these ticks. In total, 209 reptile specimens consisting of nine species of lizards and seven species of snakes were collected. Plestiodon fasciatus (L.) was the most numerous species collected (55%) followed by Sceloporus undulatus (Latreille) (17%) and Scincella lateralis (Say) (11%). Less than 10 individuals were collected for all remaining reptile species. The infestation prevalence of I. scapularis on all reptile specimens collected was 14% for larvae and 25% for nymphs. Larvae were found on lizards from April until September and peaked in May, while nymphs were found from March until September and peaked in April. I. scapularis larvae (84%) and nymphs (73%) preferentially attached to the axillae/front leg of P. fasciatus. Two chigger species, Eutrombicula splendens (Ewing) and Eutrombicula cinnabaris (Ewing), were found on 2% of the reptiles collected. No ectoparasites, including ticks, were obtained from the seven species of snakes collected.

An autochthonous case of cystic echinococcosis in Finland, 2015.

We report a case of pulmonary cystic echinococcosis in a child from eastern Finland with no history of travelling abroad. The cyst was surgically removed and the organism molecularly identified as Echinococcus canadensis genotype G10. This parasite is maintained in eastern Finland in a sylvatic life cycle involving wolves and moose; in the present case, the infection was presumably transmitted by hunting dogs.

Phylogenetic incongruence inferred with two mitochondrial genes in Mepraia spp. and Triatoma eratyrusiformis(Hemiptera, Reduviidae).

Mitochondrial DNA (mtDNA) is widely used to clarify phylogenetic relationships among and within species, and to determine population structure. Due to the linked nature of mtDNA genes it is expected that different genes will show similar results. Phylogenetic incongruence using mtDNA genes may result from processes such as heteroplasmy, nuclear integration of mitochondrial genes, polymerase errors, contamination, and recombination. In this study we used sequences from two mitochondrial genes (cytochrome b and cytochrome oxidase subunit I) from the wild vectors of Chagas disease, Triatoma eratyrusiformis and Mepraia species to test for topological congruence. The results showed some cases of phylogenetic incongruence due to misplacement of four haplotypes of four individuals. We discuss the possible causes of such incongruence and suggest that the explanation is an intra-individual variation likely due to heteroplasmy. This phenomenon is an independent evidence of common ancestry between these taxa.

Discovery of fifth serotype of dengue virus (DENV-5): A new public health dilemma in dengue control.

Dengue fever is a re-emerging public health problem with two-fifths of the world population being at risk of infection. Till now, dengue fever was believed to be caused by four different serotypes. The fifth variant DENV-5 has been isolated in October 2013. This serotype follows the sylvatic cycle unlike the other four serotypes which follow the human cycle. The likely cause of emergence of the new serotype could be genetic recombination, natural selection and genetic bottlenecks. There is no indication of the presence of DENV-5 in India. Recent clinical trials with the promising Chimerivax tetravalent vaccine suffered a setback. Discovery of DENV-5 and more such sylvatic strains in future may further impede the Dengue Vaccine Initiative. Integrated Vector Management holds the key to sustainable dengue control. Further epidemiological and ecological studies are needed to detect additional sylvatic dengue strains.

Evaluation of humoral immune response after yellow fever infection: an observational study on patients from the 2017-2018 sylvatic outbreak in Brazil.

Between 2016 and 2018, Brazil experienced major sylvatic yellow fever (YF) outbreaks that caused hundreds of casualties, with Minas Gerais (MG) being the most affected state. These outbreaks provided a unique opportunity to assess the immune response triggered by the wild-type (WT) yellow fever virus (YFV) in humans. The plaque reduction neutralization test (PRNT) is currently the standard method to assess the humoral immune response to YFV by measuring neutralizing antibodies (nAbs). The present study aimed to evaluate the humoral immune response of patients from the 2017-2018 sylvatic YF outbreak in MG with different disease outcomes by using PRNTs with a WT YFV strain, isolated from the 2017-2018 outbreak, and a vaccine YFV strain. Samples from naturally infected YF patients were tested, in comparison with healthy vaccinees. Results showed that both groups presented different levels of nAb against the WT and vaccine strains, and the levels of neutralization against the strains varied homotypically and heterotypically. Results based on the geometric mean titers (GMTs) suggest that the humoral immune response after a natural infection of YFV can reach higher levels than that induced by vaccination (GMT of patients against WT YFV compared to GMT of vaccinees, P < 0.0001). These findings suggest that the humoral immune responses triggered by the vaccine and WT strains of YFV are different, possibly due to genetic and antigenic differences between these viruses. Therefore, current means of assessing the immune response in naturally infected YF individuals and immunological surveillance methods in areas with intense viral circulation may need to be updated.IMPORTANCEYellow fever is a deadly febrile disease caused by the YFV. Despite the existence of effective vaccines, this disease still represents a public health concern worldwide. Much is known about the immune response against the vaccine strains of the YFV, but recent studies have shown that it differs from that induced by WT strains. The extent of this difference and the mechanisms behind it are still unclear. Thus, studies aimed to better understand the immune response against this virus are relevant and necessary. The present study evaluated levels of neutralizing antibodies of yellow fever patients from recent outbreaks in Brazil, in comparison with healthy vaccinees, using plaque reduction neutralization tests with WT and vaccine YFV strains. Results showed that the humoral immune response in naturally infected patients was higher than that induced by vaccination, thus providing new insights into the immune response triggered against these viruses.