Bat humoral immunity and its role in viral pathogenesis, transmission, and zoonosis.

Bats harbor viruses that can cause severe disease and death in humans including filoviruses (e.g., Ebola virus), henipaviruses (e.g., Hendra virus), and coronaviruses (e.g., SARS-CoV). Bats often tolerate these viruses without noticeable adverse immunological effects or succumbing to disease. Previous studies have largely focused on the role of the bat's innate immune response to control viral pathogenesis, but little is known about bat adaptive immunity. A key component of adaptive immunity is the humoral response, comprised of antibodies that can specifically recognize viral antigens with high affinity. The antibody genes within the 1,400 known bat species are highly diverse, and these genetic differences help shape fundamental aspects of the antibody repertoire, including starting diversity and viral antigen recognition. Whether antibodies in bats protect, mediate viral clearance, and prevent transmission within bat populations is poorly defined. Furthermore, it is unclear how neutralizing activity and Fc-mediated effector functions contribute to bat immunity. Although bats have canonical Fc genes (e.g., mu, gamma, alpha, and epsilon), the copy number and sequences of their Fc genes differ from those of humans and mice. The function of bat antibodies targeting viral antigens has been speculated based on sequencing data and polyclonal sera, but functional and biochemical data of monoclonal antibodies are lacking. In this review, we summarize current knowledge of bat humoral immunity, including variation between species, their potential protective role(s) against viral transmission and replication, and address how these antibodies may contribute to population dynamics within bats communities. A deeper understanding of bat adaptive immunity will provide insight into immune control of transmission and replication for emerging viruses with the potential for zoonotic spillover.

Human dendritic cell interactions with the zoonotic parasite Cryptosporidium parvum result in activation and maturation.

Cryptosporidiosis in humans is caused by infection of the zoonotic apicomplexan parasite Cryptosporidium parvum. In 2006, it was included by the World Health Organization (WHO) in the group of the most neglected poverty-related diseases. It is characterized by enteritis accompanied by profuse catarrhalic diarrhea with high morbidity and mortality, especially in children of developing countries under the age of 5 years and in HIV patients. The vulnerability of HIV patients indicates that a robust adaptive immune response is required to successfully fight this parasite. Little is known, however, about the adaptive immune response against C. parvum. To have an insight into the early events of the adaptive immune response, we generated primary human dendritic cells (DCs) from monocytes of healthy blood donors and exposed them to C. parvum oocysts and sporozoites in vitro. DCs are equipped with numerous receptors that detect microbial molecules and alarm signals. If stimulation is strong enough, an essential maturation process turns DCs into unique activators of naïve T cells, a prerequisite of any adaptive immune response. Parasite exposure highly induced the production of the pro-inflammatory cytokines/chemokines interleukin (IL)-6 and IL-8 in DCs. Moreover, antigen-presenting molecules (HLA-DR and CD1a), maturation markers, and costimulatory molecules required for T-cell stimulation (CD83, CD40, and CD86) and adhesion molecules (CD11b and CD58) were all upregulated. In addition, parasite-exposed human DCs showed enhanced cell adherence, increased mobility, and a boosted but time-limited phagocytosis of C. parvum oocysts and sporozoites, representing other prerequisites for antigen presentation. Unlike several other microbial stimuli, C. parvum exposure rather led to increased oxidative consumption rates (OCRs) than extracellular acidification rates (ECARs) in DCs, indicating that different metabolic pathways were used to provide energy for DC activation. Taken together, C. parvum-exposed human DCs showed all hallmarks of successful maturation, enabling them to mount an effective adaptive immune response.

A tale of endurance: bats, viruses and immune dynamics.

The emergence of highly zoonotic viral infections has propelled bat research forward. The viral outbreaks including Hendra virus, Nipah virus, Marburg virus, Ebola virus, Rabies virus, Middle East respiratory syndrome coronavirus, SARS-CoV and the latest SARS-CoV-2 have been epidemiologically linked to various bat species. Bats possess unique immunological characteristics that allow them to serve as a potential viral reservoir. Bats are also known to protect themselves against viruses and maintain their immunity. Therefore, there is a need for in-depth understanding into bat-virus biology to unravel the major factors contributing to the coexistence and spread of viruses.

Bats are the most diverse mammalian order, with over 1400 species found worldwide. Studies on bats have revealed that they frequently carry and transmit multiple viruses. They are also known to recover from viral infections. Further, human interference and climatic changes in bats' native habitat have led to virus spillover events from bats to human populations, posing a serious public health risk. A deeper understanding of the coexistence of bats and viruses, as well as the mechanisms of disease transmission to humans, is required to minimize the risk of future viral outbreaks.

Ocorrência de anticorpos anti-toxoplasma gondii em aves silvestres de três unidades de conservação federais da Paraíba e da Bahia / Occurrence of antibodies to toxoplasma gondii in wild birds from three federal conservation units of Paraíba and Bahia, Brazil

A vigilância e monitoramento de doenças em animais silvestres são imprescindíveis no contexto ambiental e de saúde pública, pois estes animais agem como sentinelas, refletindo alterações ambientais precocemente, o que proporciona maior eficácia no monitoramento ambiental e permite o acesso rápido a informações sobre as condições da área. Neste contexto, as aves são importantes no ciclo biológico do Toxoplasma gondii e na epidemiologia da toxoplasmose, principalmente porque seus tecidos representam importantes fontes de proteína na alimentação de felídeos e humanos. Objetivou-se detectar anticorpos anti-T. gondii, por meio do teste de aglutinação modificada em aves silvestres de três Unidades de Conservação (UC) Federais dos Estados da Paraíba e Bahia. No período de dezembro de 2011 a outubro de 2013 foram capturadas com redes de neblina 222 aves silvestres pertencentes a 67 espécies, 27 famílias e 12 ordens. Após a captura, foi colhido sangue de cada animal e separado o soro, que foi submetido ao Teste de Aglutinação Modificada (MAT≥1:25) utilizando taquizoítos inativados na formalina e 2-mercaptoetanol. Dentre as 222 amostras analisadas, três (1,3%) foram sororreagentes: 1 de 16 (6,2%) pipira-preta Tachyphonus rufus (título 50), 1 de 5 (20%) juriti-gemedeira Leptotila rufaxilla (título 50) e 1 de 1 (100%) caneleiro-enxofre Casiornis fuscus (título 25). Este é o primeiro relato da ocorrência de anticorpos anti-T. gondii nas referidas espécies de aves silvestres de vida livre nas duas UC Federais estudadas.

Surveillance and monitoring of wildlife pathogens are essential in the environmental context and human public health, as these animals act as sentinels, reflecting environmental changes early on, whath gives more efficient environmental monitoring and allows quick access to information on the conditions of area. Birds are important in the epidemiology and life cycle of Toxoplasma gondii, because their tissues are important source of protein in the diet of felids and humans. The objective was to determine antibodies to Toxoplasma gondii in wild birds from three Federal Conservation Units of the states of Paraíba and Bahia by Modified Agglutination Test (MAT). From December 2011 to October 2013, 222 wild birds of 67 species from 27 families and 12 Orders were captured with mist nets. Blood samples were then collected and the serum was separated by centrifugation. The sera were tested (MAT≥1:25) using formalin-fixed whole tachyzoites and 2-mercaptoethanol. Antibodies to T. gondii were found in 3 of 222 (1.3%) birds: in 1 of 16 (6.2%) white-lined tanager (Tachyphonus rufus, titer 50), in 1 of 5 (20%) gray-fronted dove (Leptotilla rufaxila, titer 50), and in 1 of 1 (100%) ashy-throated casiornis (Casiornis fuscus, titer 25). This is the first report of occurrence of antibodies to T. gondii in these tree bird species from two Federal Conservation Units.

Occurrence of antibodies to Toxoplasma gondii in opossums caught in urban areas of Bauru, state of São Paulo, Brazil / Ocorrência de anticorpos para Toxoplasma gondii em gambás capturados na área urbana de Bauru, Estado de São Paulo, Brasil

Toxoplasmosis is one of the most common zoonoses worldwide. It was initially described in rodents and rabbits. There are few data on the morbidity and mortality of this disease among Brazilian marsupial fauna, such as opossums. These animals are of great importance regarding the epidemiology of this disease, given that they are prey for felids and other carnivores. With the aim of ascertaining the serological response to Toxoplasma gondii among marsupials (Didelphis spp.), 38 animals that had been caught in 14 districts of the urban area of the municipality of Bauru, state of São Paulo, were evaluated. The modified agglutination test (MAT) showed that 26.3% (10/38) of the samples analyzed were seropositive. It can be suggested that the opossums' behavior and persistent proximity to human housing results in contact with cats and T. gondii infection, based on the frequency found in this study. This was the first study on the seroprevalence of T. gondii in opossums caught in the urban area of the municipality of Bauru, SP, and it highlights the need for environmental and health authorities of the municipality to monitor this zoonosis.(AU)

A toxoplasmose é uma das zoonoses mais comuns no mundo, tendo sido descrita inicialmente em roedores e em coelhos. Todavia, poucos são os dados sobre morbidade e mortalidade da toxoplasmose nos marsupiais da fauna brasileira, como os gambás, sendo de grande importância na epidemiologia da doença, como presas para felídeos e outros carnívoros. Com o objetivo de verificar a resposta sorológica para Toxoplasma gondii em marsupiais (Didelphis spp.), foram avaliados 38 animais capturados em 14 regiões da área urbana do município de Bauru-SP. Foi encontrada uma frequência, de acordo com o teste de aglutinação modificada (MAT), de 26,3% (10/38) nas amostras analisadas. Pode-se sugerir que o comportamento dos gambás e sua permanência próxima a habitações humanas resultam em contato com gatos e infecção por T. gondii, tendo em vista a frequência encontrada neste estudo. Este é o primeiro estudo de soroprevalência de T. gondii em gambás capturados na área urbana do município de Bauru-SP, alertando-se para a necessidade do monitoramento desta zoonose pelas autoridades de vigilância ambiental e sanitária do município.(AU)