Experimental Zika Virus Infection of Neotropical Primates

Identification of Specific Cell Surface Markers on Immune Cells of Squirrel Monkeys (Saimiri sciureus)

Nonhuman primates are an important experimental model for the development of targeted biological therapeutics because of their immunological closeness to humans. However, there are very few antibody reagents relevant for delineating the different immune cell subsets based on nonhuman primate antigens directly or with cross-reactivity to those in humans. Here, we report specific expression of HLA-DR, PD-1, and CD123 on different circulating immune cell subsets in the peripheral blood that included T cells (CD3+), T cells subsets (CD4+ and CD8+), B cells (CD20+), natural killer (NK) cells (CD3-CD16+), and natural killer T cells (CD3+CD16+) along with different monocyte subsets in squirrel monkey (Saimiri sciureus). We established cross-reactivity of commercial mouse antihuman monoclonal antibodies (mAbs), with these various immune cell surface markers. These findings should aid further future comprehensive understanding of the immune parameters and identification of new biomarkers to significantly improve SQM as a model for biomedical studies.

African ZIKV lineage fails to sustain infectivity in an in vitro mimetic urban cycle

Zika virus (ZIKV) is an arbovirus maintained in nature in two distinct cycles of transmission: urban and sylvatic. Each cycle includes specific vertebrate and invertebrate hosts, and through alternate infections, a conserved consensus sequence is maintained that might vary depending on the cycle. The current study aimed to investigate the ability of ZIKVAF and ZIKVBR to maintain an infectious cycle by alternating passages in cells mimicking the urban (UC) and semi-sylvatic (SC) cycles. The complete genome of the original inoculum and the last passages for each cycle were sequenced by Sanger. Ten passages were performed, as planned, for ZIKVBR UC, ZIKVAF SC, and ZIKVBR SC. ZIKVBR SC showed significant variation in viral titers along the passages, suggesting that the virus is not well adapted to the non-human primate host. ZIKVAF passage in UC was abrogated in the third passage, showing the inability of the African lineage to sustain cycles in human cells, suggesting a low capacity to establish an urban cycle. Several mutations were found in both strains along the passages, but not occurring at equivalent positions. Further studies are needed to elucidate whether any of these specific mutations affect viral fitness. ZIKV strains behave differently in artificial transmission cycles in vitro: Brazilian ZIKV was able to establish urban and semi-sylvatic cycles in vitro. African ZIKV proved unable to cycle among human and mosquito cells and is compatible only with the semi-sylvatic cycle. The main mutations arose in the NS2A region after artificial transmission cycles for both ZIKV strains but not at equivalent positions.

Zika Virus Infection Damages the Testes in Pubertal Common Squirrel Monkeys (Saimiri collinsi)

During the Zika virus (ZIKV) outbreak and after evidence of its sexual transmission was obtained, concerns arose about the impact of the adverse effects of ZIKV infection on human fertility. In this study, we evaluated the clinical-laboratory aspects and testicular histopathological patterns of pubertal squirrel monkeys (Saimiri collinsi) infected with ZIKV, analyzing the effects at different stages of infection. The susceptibility of S. collinsi to ZIKV infection was confirmed by laboratory tests, which detected viremia (mean 1.63 × 106 RNA copies/µL) and IgM antibody induction. Reduced fecal testosterone levels, severe testicular atrophy and prolonged orchitis were observed throughout the experiment by ultrasound. At 21 dpi, testicular damage associated with ZIKV was confirmed by histopathological and immunohistochemical (IHC) analyses. Tubular retraction, the degeneration and necrosis of somatic and germ cells in the seminiferous tubules, the proliferation of interstitial cells and an inflammatory infiltrate were observed. ZIKV antigen was identified in the same cells where tissue injuries were observed. In conclusion, squirrel monkeys were found to be susceptible to the Asian variant of ZIKV, and this model enabled the identification of multifocal lesions in the seminiferous tubules of the infected group evaluated. These findings may suggest an impact of ZIKV infection on male fertility.

Experimental Yellow Fever in Squirrel Monkey: Characterization of Liver In Situ Immune Response

Non-human primates contribute to the spread of yellow fever virus (YFV) and the establishment of transmission cycles in endemic areas, such as Brazil. This study aims to investigate virological, histopathological and immunohistochemical findings in livers of squirrel monkeys (Saimiri spp.) infected with the YFV. Viremia occurred 1-30 days post infection (dpi) and the virus showed a predilection for the middle zone (Z2). The livers were jaundiced with subcapsular and hemorrhagic multifocal petechiae. Apoptosis, lytic and coagulative necrosis, steatosis and cellular edema were also observed. The immune response was characterized by the expression of S100, CD11b, CD57, CD4 and CD20; endothelial markers; stress and cell death; pro and anti-inflammatory cytokines, as well as Treg (IL-35) and IL-17 throughout the experimental period. Lesions during the severe phase of the disease were associated with excessive production of apoptotic pro-inflammatory cytokines, such as IFN-γ and TNF-α, released by inflammatory response cells (CD4+ and CD8+ T lymphocytes) and associated with high expression of molecules of adhesion in the inflammatory foci observed in Z2. Immunostaining of the local endothelium in vascular cells and the bile duct was intense, suggesting a fundamental role in liver damage and in the pathogenesis of the disease.

Detection of early myocardial cell death in owl monkeys (Aotus nancymai) using complement component C9 immunohistochemistry in formalin-fixed paraffin-embedded heart tissues: A retrospective study

BACKGROUND

Owl monkeys are commonly used in biomedical research which is affected by the high incidence of cardiomyopathy in this species. Occasionally, owl monkeys with no clinical signs of heart disease are found dead and at necropsy show no, or very mild, cardiomyopathy. A possible explanation for sudden death is acute myocardial infarction; however, early myocardial changes may be difficult to assess by conventional stains and light microscopy.

METHODS

Complement component C9 immunohistochemistry was performed in paraffin-embedded heart tissue samples from owl monkeys who died suddenly, or were euthanized due to sickness, to determine whether these animals suffered from acute myocardial infarcts.

RESULTS AND CONCLUSION

C9 deposits were found in the myocardium of 19 out of 20 (95%) animals. The findings in this study suggest owl monkeys suffer from acute myocardial infarcts, and complement component C9 immunohistochemistry may be a useful diagnostic tool.

The Impact of Deforestation, Urbanization, and Changing Land Use Patterns on the Ecology of Mosquito and Tick-Borne Diseases in Central America

Central America is a unique geographical region that connects North and South America, enclosed by the Caribbean Sea to the East, and the Pacific Ocean to the West. This region, encompassing Belize, Costa Rica, Guatemala, El Salvador, Honduras, Panama, and Nicaragua, is highly vulnerable to the emergence or resurgence of mosquito-borne and tick-borne diseases due to a combination of key ecological and socioeconomic determinants acting together, often in a synergistic fashion. Of particular interest are the effects of land use changes, such as deforestation-driven urbanization and forest degradation, on the incidence and prevalence of these diseases, which are not well understood. In recent years, parts of Central America have experienced social and economic improvements; however, the region still faces major challenges in developing effective strategies and significant investments in public health infrastructure to prevent and control these diseases. In this article, we review the current knowledge and potential impacts of deforestation, urbanization, and other land use changes on mosquito-borne and tick-borne disease transmission in Central America and how these anthropogenic drivers could affect the risk for disease emergence and resurgence in the region. These issues are addressed in the context of other interconnected environmental and social challenges.

Pathogenesis and virulence of flavivirus infections

The Flavivirus genus consists of >70 members including several that are considered significant human pathogens. Flaviviruses display a broad spectrum of diseases that can be roughly categorised into two phenotypes - systemic disease involving haemorrhage exemplified by dengue and yellow Fever virus, and neurological complications associated with the likes of West Nile and Zika viruses. Attempts to develop vaccines have been variably successful against some. Besides, mosquito-borne flaviviruses can be vertically transmitted in the arthropods, enabling long term persistence and the possibility of re-emergence. Therefore, developing strategies to combat disease is imperative even if vaccines become available. The cellular interactions of flaviviruses with their human hosts are key to establishing the viral lifecycle on the one hand, and activation of host immunity on the other. The latter should ideally eradicate infection, but often leads to immunopathological and neurological consequences. In this review, we use Dengue and Zika viruses to discuss what we have learned about the cellular and molecular determinants of the viral lifecycle and the accompanying immunopathology, while highlighting current knowledge gaps which need to be addressed in future studies.

NS2B-NS3 protease inhibitors as promising compounds in the development of antivirals against Zika virus: A systematic review

Zika virus (ZIKV) infections are associated with severe neurological complications and are a global public health concern. There are no approved vaccines or antiviral drugs to inhibit ZIKV replication. NS2B-NS3 protease (NS2B-NS3 pro), which is essential for viral replication, is a promising molecular target for anti-ZIKV drugs. We conducted a systematic review to identify compounds with promising effects against ZIKV; we discussed their pharmacodynamic and pharmacophoric characteristics. The online search, performed using the PubMed/MEDLINE and SCOPUS databases, yielded 56 articles; seven relevant studies that reported nine promising compounds with inhibitory activity against ZIKV NS2B-NS3 pro were selected. Of these, five (niclosamide, nitazoxanide, bromocriptine, temoporfin, and novobiocin) are currently available on the market and have been tested for off-label use against ZIKV. The 50% inhibitory concentration values of these compounds for the inhibition of NS2B-NS3 pro ranged at 0.38-21.6 µM; most compounds exhibited noncompetitive inhibition (66%). All compounds that could inhibit the NS2B-NS3 pro complex showed potent in vitro anti-ZIKV activity with a 50% effective concentration ranging 0.024-50 µM. The 50% cytotoxic concentration of the compounds assayed using A549, Vero, and WRL-69 cell lines ranged at 0.6-1388.02 µM and the selectivity index was 3.07-1698. This review summarizes the most promising antiviral agents against ZIKV that have inhibitory activity against viral proteases.

Three Immunocompetent Small Animal Models That Do Not Support Zika Virus Infection

Zika virus (ZIKV) is a mosquito-borne flavivirus that is primarily transmitted to humans through the bite of an infected mosquito. ZIKV causes disease in infected humans with added complications of Guillain-Barré syndrome and birth defects in infants born to mothers infected during pregnancy. There are several large immunocompetent animal models for ZIKV including non-human primates (NHPs). NHP models closely reflect human infection; however, due to sample size restrictions, investigations into the effects of transmission route and the impacts on disease dynamics have been understudied. Mice have been widely used for modeling ZIKV infection, yet there are few ZIKV-susceptible immunocompetent mouse models and none of these have been used to investigate sexual transmission. In an effort to identify a small immunocompetent animal model to characterize sexual transmission of ZIKV, we attempt experimental infection of multimammate mice, New Zealand white rabbits, and Hartley guinea pigs. The multimammate mouse is the natural reservoir of Lassa fever virus and has been identified to harbor other human pathogens. Likewise, while NZW rabbits are susceptible to West Nile virus, they have not yet been examined for their susceptibility to infection with ZIKV. Guinea pigs have been successfully used as models for ZIKV infection, but only in immunocompromised life stages (young or pregnant). Here, it was found that the multimammate mouse and New Zealand White (NZW) rabbits are not susceptible ZIKV infection as determined by a lack viral RNA in tissues and fluids collected. Sexually mature male Hartley guinea pigs were inoculated subcutaneously and by mosquito bite, but found to be refractory to ZIKV infection, contrary to findings of other studies in young and pregnant guinea pigs. Interestingly, here it is shown that adult male guinea pigs are not susceptible to ZIKV infection, even when infected by natural route (e.g., mosquito bite). Although a new small animal model for the sexual transmission for ZIKV was not established through this study, these findings provide information on outbred animal species that are not permissive to infection (NZW rabbits and multimammate mice) and new information surrounding limitations of a previously established animal model (guinea pigs).

Non-human Primate Models to Investigate Mechanisms of Infection-Associated Fetal and Pediatric Injury, Teratogenesis and Stillbirth

A wide array of pathogens has the potential to injure the fetus and induce teratogenesis, the process by which mutations in fetal somatic cells lead to congenital malformations. Rubella virus was the first infectious disease to be linked to congenital malformations due to an infection in pregnancy, which can include congenital cataracts, microcephaly, hearing impairment and congenital heart disease. Currently, human cytomegalovirus (HCMV) is the leading infectious cause of congenital malformations globally, affecting 1 in every 200 infants. However, our knowledge of teratogenic viruses and pathogens is far from complete. New emerging infectious diseases may induce teratogenesis, similar to Zika virus (ZIKV) that caused a global pandemic in 2016-2017; thousands of neonates were born with congenital microcephaly due to ZIKV exposure in utero, which also included a spectrum of injuries to the brain, eyes and spinal cord. In addition to congenital anomalies, permanent injury to fetal and neonatal organs, preterm birth, stillbirth and spontaneous abortion are known consequences of a broader group of infectious diseases including group B streptococcus (GBS), Listeria monocytogenes, Influenza A virus (IAV), and Human Immunodeficiency Virus (HIV). Animal models are crucial for determining the mechanism of how these various infectious diseases induce teratogenesis or organ injury, as well as testing novel therapeutics for fetal or neonatal protection. Other mammalian models differ in many respects from human pregnancy including placentation, labor physiology, reproductive tract anatomy, timeline of fetal development and reproductive toxicology. In contrast, non-human primates (NHP) most closely resemble human pregnancy and exhibit key similarities that make them ideal for research to discover the mechanisms of injury and for testing vaccines and therapeutics to prevent teratogenesis, fetal and neonatal injury and adverse pregnancy outcomes (e.g., stillbirth or spontaneous abortion). In this review, we emphasize key contributions of the NHP model pre-clinical research for ZIKV, HCMV, HIV, IAV, L. monocytogenes, Ureaplasma species, and GBS. This work represents the foundation for development and testing of preventative and therapeutic strategies to inhibit infectious injury of human fetuses and neonates.

Histopathological lesions of congenital Zika syndrome in newborn squirrel monkeys

The absence of an adequate animal model for studies has limited the understanding of congenital Zika syndrome (CZS) in humans during the outbreak in America. In this study, we used squirrel monkeys (Saimiri collinsi), a neotropical primate (which mimics the stages of human pregnancy), as a model of Zika virus (ZIKV) infection. Seven pregnant female squirrel monkeys were experimentally infected at three different gestational stages, and we were able reproduce a broad range of clinical manifestations of ZIKV lesions observed in newborn humans. Histopathological and immunohistochemical analyses of early-infected newborns (2/4) revealed damage to various areas of the brain and ZIKV antigens in the cytoplasm of neurons and glial cells, indicative of CZS. The changes caused by ZIKV infection were intrauterine developmental delay, ventriculomegaly, simplified brain gyri, vascular impairment and neuroprogenitor cell dysfunction. Our data show that the ZIKV infection outcome in squirrel monkeys is similar to that in humans, indicating that this model can be used to help answer questions about the effect of ZIKV infection on neuroembryonic development and the morphological changes induced by CZS.

Biochemistry, Doppler echocardiography, and electrocardiography evaluation in captive owl monkeys (Aotus sp)

BACKGROUND

The cardiovascular system of owl monkeys has been studied due to frequent postmortem findings of heart disease in asymptomatic animals. The silent aspect and the difficulty of early diagnosis intensify the importance of studying the cardiovascular system in this species.

METHODS

Echocardiogram evaluation was carried out on 60 animals, grouped into suspect or non-suspect of having heart diseases, and evaluated through electrocardiogram, hematology, and biochemical tests.

RESULTS

Doppler echocardiography indicated two animals with suspicion of left ventricular hypertrophy and eight with dilated cardiomyopathy. Suspect animals had higher cardiac measurements and reduced shortening fraction. Troponin I was detectable in two animals (0.128 ng/mL and 0.584 ng/mL), and serum albumin concentration was significantly higher in non-suspect animals (P < .05).

CONCLUSIONS

The importance of echocardiographic measurements of IVSd, IVSs, LVIDd, LVIDs, LVPWd, LVPWs, LA, EF, and FS in the cardiac evaluation of captive owl monkeys was evidenced.

Prenatal disorders and congenital Zika syndrome in squirrel monkeys

During the Zika virus (ZIKV) outbreak in Brazil (2015–2016), the clinical manifestations associated with its infection were complex and included miscarriage and congenital malformations, not previously described. In this study, we evaluated the prenatal conditions of pregnant female squirrel monkeys (Saimiri collinsi) infected during different gestational thirds (GTs) and assessed all clinical aspects, diagnostic imaging, viremia and the immune response. In our study, 75% of the infected animals in the 1st GT group had significant clinical manifestations, such as miscarriage and prolonged viremia associated with a late immune response. Consequently, their neonates showed fetal neuropathology, such as cerebral hemorrhage, lissencephaly or malformations of the brain grooves, ventriculomegaly, and craniofacial malformations. Thus, our study demonstrated the relevance of pregnant squirrel monkeys as a model for the study of ZIKV infection in neonates due to the broad clinical manifestations presented, including the typical congenital Zika syndrome manifestations described in humans.

The vertical stratification of potential bridge vectors of mosquito-borne viruses in a central Amazonian forest bordering Manaus, Brazil

The emergence of Zika virus (ZIKV) in Latin America brought to the fore longstanding concerns that forests bordering urban areas may provide a gateway for arbovirus spillback from humans to wildlife. To bridge urban and sylvatic transmission cycles, mosquitoes must co-occur with both humans and potential wildlife hosts, such as monkeys, in space and time. We deployed BG-Sentinel traps at heights of 0, 5, 10, and 15 m in trees in a rainforest reserve bordering Manaus, Brazil, to characterize the vertical stratification of mosquitoes and their associations with microclimate and to identify potential bridge vectors. Haemagogus janthinomys and Sabethes chloropterus, two known flavivirus vectors, showed significant stratification, occurring most frequently above the ground. Psorophora amazonica, a poorly studied anthropophilic species of unknown vector status, showed no stratification and was the most abundant species at all heights sampled. High temperatures and low humidity are common features of forest edges and microclimate analyses revealed negative associations between minimum relative humidity, which was inversely correlated with maximum temperature, and the occurrence of Haemagogus and Sabethes mosquitoes. In this reserve, human habitations border the forest while tamarin and capuchin monkeys are also common to edge habitats, creating opportunities for the spillback of mosquito-borne viruses.

Ecological processes underlying the emergence of novel enzootic cycles: Arboviruses in the neotropics as a case study

Pathogens originating from wildlife (zoonoses) pose a significant public health burden, comprising the majority of emerging infectious diseases. Efforts to control and prevent zoonotic disease have traditionally focused on animal-to-human transmission, or "spillover." However, in the modern era, increasing international mobility and commerce facilitate the spread of infected humans, nonhuman animals (hereafter animals), and their products worldwide, thereby increasing the risk that zoonoses will be introduced to new geographic areas. Imported zoonoses can potentially "spill back" to infect local wildlife-a danger magnified by urbanization and other anthropogenic pressures that increase contacts between human and wildlife populations. In this way, humans can function as vectors, dispersing zoonoses from their ancestral enzootic systems to establish reservoirs elsewhere in novel animal host populations. Once established, these enzootic cycles are largely unassailable by standard control measures and have the potential to feed human epidemics. Understanding when and why translocated zoonoses establish novel enzootic cycles requires disentangling ecologically complex and stochastic interactions between the zoonosis, the human population, and the natural ecosystem. In this Review, we address this challenge by delineating potential ecological mechanisms affecting each stage of enzootic establishment-wildlife exposure, enzootic infection, and persistence-applying existing ecological concepts from epidemiology, invasion biology, and population ecology. We ground our discussion in the neotropics, where four arthropod-borne viruses (arboviruses) of zoonotic origin-yellow fever, dengue, chikungunya, and Zika viruses-have separately been introduced into the human population. This paper is a step towards developing a framework for predicting and preventing novel enzootic cycles in the face of zoonotic translocations.

Into the woods: Changes in mosquito community composition and presence of key vectors at increasing distances from the urban edge in urban forest parks in Manaus, Brazil

Mosquito-borne Zika virus (ZIKV) was recently introduced into the Americas and now has the potential to spill back into a sylvatic cycle in the region, likely involving non-human primates and Aedes, Haemagogus, and Sabethes species mosquitoes. We investigated potential routes of mosquito-borne virus exchange between urban and sylvatic transmission cycles by characterizing mosquito communities in three urban forest parks that receive heavy traffic from both humans and monkeys in Manaus, Brazil. Parks were stratified by both distance from the urban-forest edge (0, 50, 100, and 500 m) and relative Normalized Difference Vegetation Index (NDVI) (low, medium, or high), and mosquitoes were sampled at randomly selected sites within each stratum using BG-Sentinel traps. Additionally, temperature, relative humidity, and other environmental data were collected at each site. A total of 1,172 mosquitoes were collected from 184 sites sampled in 2018, of which 98 sites were resampled in 2019. Using park as the unit of replication (i.e. 3 replicates per sampling stratum), a two-way ANOVA showed no effect of distance or NDVI on the mean number of identified species (P > 0.05 for both comparisons) or on species diversity as measured by the Shannon-Wiener diversity index (P > 0.10 for both comparisons). However, the Morisita overlap index revealed that mosquito communities changed substantially with increasing distance from edge, with communities at 0 m and 500 m being quite distinct. Aedes albopictus and Ae. aegypti penetrated at least 100 m into the forest, while forest specialists including Haemagogus janthinomys, Sabethes glaucodaemon, and Sa. tridentatus were detected in low numbers within 100 m from the forest edge. Trichoprosopon digitatum and Psorophora amazonica were among the most abundant species collected, and both showed distributions extending from the forest edge to its interior. Our results show overlapping distributions of urban and forest mosquitoes at park edges, which highlights the risk of arbovirus exchange via multiple bridge vectors in Brazilian urban forest parks. These parks may also provide refugia for both Ae. albopictus and Ae. aegypti from mosquito control programs.

Survey on Non-Human Primates and Mosquitoes Does not Provide Evidences of Spillover/Spillback between the Urban and Sylvatic Cycles of Yellow Fever and Zika Viruses Following Severe Outbreaks in Southeast Brazil

In the last decade, Flaviviruses such as yellow fever (YFV) and Zika (ZIKV) have expanded their transmission areas. These viruses originated in Africa, where they exhibit both sylvatic and interhuman transmission cycles. In Brazil, the risk of YFV urbanization has grown, with the sylvatic transmission approaching the most densely populated metropolis, while concern about ZIKV spillback to a sylvatic cycle has risen. To investigate these health threats, we carried out extensive collections and arbovirus screening of 144 free-living, non-human primates (NHPs) and 5219 mosquitoes before, during, and after ZIKV and YFV outbreaks (2015-2018) in southeast Brazil. ZIKV infection was not detected in any NHP collected at any time. In contrast, current and previous YFV infections were detected in NHPs sampled between 2017 and 2018, but not before the onset of the YFV outbreak. Mosquito pools screened by high-throughput PCR were positive for YFV when captured in the wild and during the YFV outbreak, but were negative for 94 other arboviruses, including ZIKV, regardless of the time of collection. In conclusion, there was no evidence of YFV transmission in coastal southeast Brazil before the current outbreak, nor the spread or establishment of an independent sylvatic cycle of ZIKV or urban Aedes aegypti transmission of YFV in the region. In view of the region's receptivity and vulnerability to arbovirus transmission, surveillance of NHPs and mosquitoes should be strengthened and continuous.

Low vector competence in sylvatic mosquitoes limits Zika virus to initiate an enzootic cycle in South America

Zika virus (ZIKV) has spread in the Americas since 2015 and the potential establishment of a sylvatic transmission cycle in the continent has been hypothesized. We evaluated vector competence of five sylvatic Neotropical mosquito species to two ZIKV isolates. Distinct batches of Haemagogus leucoceleanus, Sabethes albiprivus, Sabethes identicus, Aedes terrens and Aedes scapularis females were respectively orally challenged and inoculated intrathoracically with ZIKV. Orally challenged mosquitoes were refractory or exhibited low infection rates. Viral dissemination was detected only in Hg. leucocelaenus, but with very low rates. Virus was not detected in saliva of any mosquito orally challenged with ZIKV, regardless of viral isolate and incubation time. When intrathoracically injected, ZIKV disseminated in high rates in Hg. leucocelaenus, Sa. identicus and Sa. albpiprivus, but low transmission was detected in these species; very low dissemination and no transmission was detected in Ae. terrens and Ae. scapularis. Together these results suggest that genetically determined tissue barriers, especially in the midgut, play a vital role in inhibiting ZIKV for transmission in the tested sylvatic mosquito species. Thus, an independent enzootic transmission cycle for ZIKV in South America is very unlikely.

High susceptibility, viral dynamics and persistence of South American Zika virus in New World monkey species

South American Zika virus (ZIKV) recently emerged as a novel human pathogen, linked with neurological disorders. However, comparative ZIKV infectivity studies in New World primates are lacking. Two members of the Callitrichidae family, common marmosets (Callithrix jacchus) and red-bellied tamarins (Saguinus labiatus), were highly susceptible to sub-cutaneous challenge with the Puerto Rico-origin ZIKV_PRVABC59 strain. Both exhibited rapid, high, acute viraemia with early neuroinvasion (3 days) in peripheral and central nervous tissue. ZIKV RNA levels in blood and tissues were significantly higher in New World hosts compared to Old World species (Macaca mulatta, Macaca fascicularis). Tamarins and rhesus macaques exhibited loss of zonal occludens-1 (ZO-1) staining, indicative of a compromised blood-brain barrier 3 days post-ZIKV exposure. Early, widespread dissemination across multiple anatomical sites distant to the inoculation site preceded extensive ZIKV persistence after 100 days in New and Old World lineages, especially lymphoid, neurological and reproductive sites. Prolonged persistence in brain tissue has implications for otherwise resolved human ZIKV infection. High susceptibility of distinct New World species underscores possible establishment of ZIKV sylvatic cycles in primates indigenous to ZIKV endemic regions. Tamarins and marmosets represent viable New World models for ZIKV pathogenesis and therapeutic intervention studies, including vaccines, with contemporary strains.

Meeting report: 32nd International Conference on Antiviral Research

The 32nd International Conference on Antiviral Research (ICAR), sponsored by the International Society for Antiviral Research (ISAR), was held in Baltimore, Maryland, USA, on May 12-15, 2019. This report gives an overview of the conference on behalf of the Society. It provides a general review of the meeting and awardees, summarizing the presentations, and their main conclusions from the perspective of researchers active in many different areas of antiviral research and development. As in past years, ICAR promoted and showcased the most recent progress in antiviral research, and continued to foster collaborations and interactions in drug discovery and development. The 33rd ICAR will be held in Seattle, Washington, USA, March 30th-April 3rd, 2020.

Vector-borne transmission and evolution of Zika virus

Zika virus (ZIKV), discovered in the Zika Forest of Uganda in 1947, is a mosquito-borne flavivirus related to yellow fever, dengue and West Nile viruses. From its discovery until 2007, only sporadic ZIKV cases were reported, with mild clinical manifestations in patients. Therefore, little attention was given to this virus before epidemics in the South Pacific and the Americas that began in 2013. Despite a growing number of ZIKV studies in the past three years, many aspects of the virus remain poorly characterized, particularly the spectrum of species involved in its transmission cycles. Here, we review the mosquito and vertebrate host species potentially involved in ZIKV vector-borne transmission worldwide. We also provide an evidence-supported analysis regarding the possibility of ZIKV spillback from an urban cycle to a zoonotic cycle outside Africa, and we review hypotheses regarding recent emergence and evolution of ZIKV. Finally, we identify critical remaining gaps in the current knowledge of ZIKV vector-borne transmission.

Zika Virus in Peridomestic Neotropical Primates, Northeast Brazil

Zika virus (ZIKV) is a mosquito-borne viral disease associated with fetal microcephaly and other central nervous system (CNS) symptomatology. It was first identified in a Rhesus macaque in Uganda in 1947 and later in humans (Zika fever). In 2015, ZIKV was notified in Northeast Brazil where it was associated with CNS alterations and with rapid epidemic spread. Considering that ZIKV infects Old World monkeys, the aim of this study was to follow its potential in neotropical primates. Here, we show the detection of ZIKV in marmosets and capuchin monkeys captured in Ceara state, Northeast Brazil. Nine (9/132) samples were positive by quantitative RT-PCR assay. Neutralizing antibodies in primates for ZIKV were also detected by PRNT. The ZIKV-positive samples were obtained from peridomestic animals captured in proximity to humans in areas with reports of ZIKV-associated microcephaly cases during the epidemic period. These results reiterate the molecular evidence of ZIKV infection in neotropical primates, and the temporal detection suggests that detection in primates occurred during the epidemic period in humans. However, a continuous surveillance is necessary to exclude the possibility of virus circulation and transmission in wild environments.

A 'Furry-Tale' of Zika Virus Infection: What Have We Learned from Animal Models?

The worldwide attention that the Zika virus (ZIKV) attracted, following its declaration as a Public Health Emergency of International concern by WHO in 2016, has led to a large collective effort by the international scientific community to understand its biology. Despite the mild symptoms caused by ZIKV in most infected people, the virus displays a number of worrying features, such as its ability to cause transplacental infection, fetal abnormalities and vector independent transmission through body fluids. In addition, the virus has been associated with the induction of Guillain-Barre syndrome in a number of infected individuals. With travelling, the virus has spread outside the original ZIKV endemic areas making it imperative to find ways to control it. Thus far, the large number of animal models developed to study ZIKV pathogenesis have proven to be valuable tools in understanding how the virus replicates and manifests itself in the host, its tissue tropism and the type of immune responses it induces. Still, vital questions, such as the molecular mechanisms of ZIKV persistence and the long-term consequences of ZIKV infection in the developing brain, remain unanswered. Here, we reviewed and discussed the major and most recent findings coming from animal studies and their implications for a ZIKV vaccine design.

Methods for detecting Zika virus in feces: A case study in captive squirrel monkeys (Saimiri boliviensis boliviensis)

A strain of Zika virus (ZIKV) of Asian origin associated with birth defects and neurological disorders has emerged and spread through the Americas. ZIKV was first isolated in the blood of nonhuman primates in Africa and has been detected in the blood, saliva, and urine of a few catarrhine species in both Africa and Asia, suggesting that nonhuman primates may serve as both a source and a reservoir of the virus. The recent introduction of ZIKV to human populations in the Americas presents the potential for the virus to spread into nonhuman primate reservoirs. Thus, it is critical to develop efficient and noninvasive detection methods to monitor the spread of the virus in wild nonhuman primate populations. Here, we describe a method for ZIKV detection in noninvasively collected fecal samples of a Neotropical primate. Fecal samples were collected from two captive squirrel monkeys (Saimiri boliviensis boliviensis) that were experimentally infected with ZIKV (Strain Mexico_1_44) and an additional two uninfected squirrel monkeys. Nucleic acids were extracted from these samples, and RT-qPCR was used to assay for the presence of ZIKV using primers flanking a 101 bp region of the NS5 gene. In both ZIKV-inoculated animals, ZIKV was detected 5-11 days post-infection, but was not detected in the uninfected animals. We compare the fecal results to ZIKV detection in serum, saliva, and urine samples from the same individuals. Our results indicate that fecal detection is a cost-effective, noninvasive method for monitoring wild populations of Neotropical primates as possible ZIKV reservoirs.

Cytokine-Mediated Tissue Injury in Non-human Primate Models of Viral Infections

Viral infections trigger robust secretion of interferons and other antiviral cytokines by infected and bystander cells, which in turn can tune the immune response and may lead to viral clearance or immune suppression. However, aberrant or unrestricted cytokine responses can damage host tissues, leading to organ dysfunction, and even death. To understand the cytokine milieu and immune responses in infected host tissues, non-human primate (NHP) models have emerged as important tools. NHP have been used for decades to study human infections and have played significant roles in the development of vaccines, drug therapies and other immune treatment modalities, aided by an ability to control disease parameters, and unrestricted tissue access. In addition to the genetic and physiological similarities with humans, NHP have conserved immunologic properties with over 90% amino acid similarity for most cytokines. For example, human-like symptomology and acute respiratory syndrome is found in cynomolgus macaques infected with highly pathogenic avian influenza virus, antibody enhanced dengue disease is common in neotropical primates, and in NHP models of viral hepatitis cytokine-induced inflammation induces severe liver damage, fibrosis, and hepatocellular carcinoma recapitulates human disease. To regulate inflammation, anti-cytokine therapy studies in NHP are underway and will provide important insights for future human interventions. This review will provide a comprehensive outline of the cytokine-mediated exacerbation of disease and tissue damage in NHP models of viral infections and therapeutic strategies that can aid in prevention/treatment of the disease syndromes.

ZIKV Demonstrates Minimal Pathologic Effects and Mosquito Infectivity in Viremic Cynomolgus Macaques

To evaluate the effects of ZIKV infection on non-human primates (NHPs), as well as to investigate whether these NHPs develop sufficient viremia to infect the major urban vector mosquito, Aedes aegypti, four cynomolgus macaques (Macaca fascicularis) were subcutaneously infected with 5.0 log₁₀ focus-forming units (FFU) of DNA clone-derived ZIKV strain FSS13025 (Asian lineage, Cambodia, 2010). Following infection, the animals were sampled (blood, urine, tears, and saliva), underwent daily health monitoring, and were exposed to Ae. aegypti at specified time points. All four animals developed viremia, which peaked 3⁻4 days post-infection at a maximum value of 6.9 log₁₀ genome copies/mL. No virus was detected in urine, tears, or saliva. Infection by ZIKV caused minimal overt disease: serum biochemistry and CBC values largely fell within the normal ranges, and cytokine elevations were minimal. Strikingly, the minimally colonized population of Ae. aegypti exposed to viremic animals demonstrated a maximum infection rate of 26% during peak viremia, with two of the four macaques failing to infect a single mosquito at any time point. These data indicate that cynomolgus macaques may be an effective model for ZIKV infection of humans and highlights the relative refractoriness of Ae. aegypti for ZIKV infection at the levels of viremia observed.

Evidence of natural Zika virus infection in neotropical non-human primates in Brazil

In Africa, Old World Primates are involved in the maintenance of sylvatic circulation of ZIKV. However, in Brazil, the hosts for the sylvatic cycle remain unknown. We hypothesized that free-living NHPs might play a role in urban/periurban ZIKV dynamics, thus we undertook an NHP ZIKV investigation in two cities in Brazil. We identified ZIKV-positive NHPs and sequences obtained were phylogenetically related to the American lineage of ZIKV. Additionally, we inoculated four C. penicillata with ZIKV and our results demonstrated that marmosets had a sustained viremia. The natural and experimental infection of NHPs with ZIKV, support the hypothesis that NHPs may be a vertebrate host in the maintainance of ZIKV transmission/circulation in urban tropical settings. Further studies are needed to understand the role they may play in maintaining the urban cycle of the ZIKV and how they may be a conduit in establishing an enzootic transmission cycle in tropical Latin America.

Colonized Sabethes cyaneus, a Sylvatic New World Mosquito Species, Shows a Low Vector Competence for Zika Virus Relative to Aedes aegypti

The introduction of Zika virus (ZIKV) to the Americas raised concern that the virus would spill back from human transmission, perpetuated by Aedes aegypti, into a sylvatic cycle maintained in wildlife and forest-living mosquitoes. In the Americas, Sabethes species are vectors of sylvatic yellow fever virus (YFV) and are therefore candidate vectors of a sylvatic ZIKV cycle. To test the potential of Sabethes cyaneus to transmit ZIKV, Sa. cyaneus and Ae. aegypti were fed on A129 mice one or two days post-infection (dpi) with a ZIKV isolate from Mexico. Sa. cyaneus were sampled at 3, 4, 5, 7, 14, and 21 days post-feeding (dpf) and Ae. aegypti were sampled at 14 and 21 dpf. ZIKV was quantified in mosquito bodies, legs, and saliva to measure infection, dissemination, and potential transmission, respectively. Of 69 Sa. cyaneus that fed, ZIKV was detected in only one, in all body compartments, at 21 dpf. In contrast, at 14 dpf 100% of 20 Ae. aegypti that fed on mice at 2 dpi were infected and 70% had virus in saliva. These data demonstrate that Sa. cyaneus is a competent vector for ZIKV, albeit much less competent than Ae. aegypti.

Translational Model of Zika Virus Disease in Baboons

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus with devastating outcomes seen recently in the Americas due to the association of maternal ZIKV infection with fetal microcephaly and other fetal malformations not previously associated with flavivirus infections. Here, we have developed the olive baboon (Papio anubis) as a nonhuman primate (NHP) translational model for the study of ZIKV pathogenesis and associated disease outcomes to contrast and compare with humans and other major NHPs, such as macaques. Following subcutaneous inoculation of adult male and nonpregnant female baboons, viremia was detected at 3 and 4 days postinfection (dpi) with the concordant presentation of a visible rash and conjunctivitis, similar to human ZIKV infection. Furthermore, virus was detected in the mucosa and cerebrospinal fluid. A robust ZIKV-specific IgM and IgG antibody response was also observed in all the animals. These data show striking similarity between humans and the olive baboon following infection with ZIKV, suggesting our model is a suitable translational NHP model to study ZIKV pathogenesis and potential therapeutics.IMPORTANCE ZIKV was first identified in 1947 in a sentinel rhesus monkey in Uganda and subsequently spread to Southeast Asia. Until 2007, only a small number of cases were reported, and ZIKV infection was relatively minor until the South Pacific and Brazilian outbreaks, where more severe outcomes were reported. Here, we present the baboon as a nonhuman primate model for contrast and comparison with other published animal models of ZIKV, such as the mouse and macaque species. Baboons breed year round and are not currently a primary nonhuman primate species used in biomedical research, making them more readily available for studies other than human immunodeficiency virus studies, which many macaque species are designated for. This, taken together with the similarities baboons have with humans, such as immunology, reproduction, genetics, and size, makes the baboon an attractive NHP model for ZIKV studies in comparison to other nonhuman primates.

Recently integrated Alu insertions in the squirrel monkey (Saimiri) lineage and application for population analyses

BACKGROUND

The evolution of Alu elements has been ongoing in primate lineages and Alu insertion polymorphisms are widely used in phylogenetic and population genetics studies. Alu subfamilies in the squirrel monkey (Saimiri), a New World Monkey (NWM), were recently reported. Squirrel monkeys are commonly used in biomedical research and often require species identification. The purpose of this study was two-fold: 1) Perform locus-specific PCR analyses on recently integrated Alu insertions in Saimiri to determine their amplification dynamics, and 2) Identify a subset of Alu insertion polymorphisms with species informative allele frequency distributions between the Saimiri sciureus and Saimiri boliviensis groups.

RESULTS

PCR analyses were performed on a DNA panel of 32 squirrel monkey individuals for 382 Alu insertion events ≤2% diverged from 46 different Alu subfamily consensus sequences, 25 Saimiri specific and 21 NWM specific Alu subfamilies. Of the 382 loci, 110 were polymorphic for presence / absence among squirrel monkey individuals, 35 elements from 14 different Saimiri specific Alu subfamilies and 75 elements from 19 different NWM specific Alu subfamilies (13 of 46 subfamilies analyzed did not contain polymorphic insertions). Of the 110 Alu insertion polymorphisms, 51 had species informative allele frequency distributions between Saimiri sciureus and Saimiri boliviensis groups.

CONCLUSIONS

This study confirms the evolution of Alu subfamilies in Saimiri and provides evidence for an ongoing and prolific expansion of these elements in Saimiri with many active subfamilies concurrently propagating. The subset of polymorphic Alu insertions with species informative allele frequency distribution between Saimiri sciureus and Saimiri boliviensis will be instructive for specimen identification and conservation biology.

Limited Evidence for Infection of Urban and Peri-urban Nonhuman Primates with Zika and Chikungunya Viruses in Brazil

Chikungunya virus (CHIKV) and Zika virus (ZIKV) emerged in the Americas in 2013. Limited antigenic variability of CHIKV and ZIKV may restrict urban transmission cycles due to population protective immunity. In Africa, sylvatic transmission cycles involving nonhuman primates (NHP) are known for CHIKV and ZIKV, causing cyclic reemergence in humans. To evaluate whether sylvatic cycles can be expected in Latin America, we tested 207 NHP collected between 2012 and 2017 in urban and peri-urban settings in Brazil for infection with ZIKV and CHIKV. No animal tested positive for viral RNA in genus-specific and species-specific reverse transcription-PCR (RT-PCR) assays. In contrast, six animals (2.9%) from the families Atelidae, Callitrichidae, and Cebidae showed ZIKV-specific antibodies and 11 (5.3%) showed CHIKV-specific antibodies in plaque reduction neutralization tests (PRNT). Reactivity was monotypic against either ZIKV or CHIKV in all cases, opposing unspecific virucidal activity of sera. PRNT endpoint titers were low at 1:40 in all NHP, and positive specimens did not correspond to the likely dispersal route and time of introduction of both arboviruses. All antibody-positive samples were therefore tested against the NHP-associated yellow fever virus (YFV) and Mayaro virus (MAYV) and against the human-associated dengue virus (DENV) by PRNT. Two ZIKV-positive samples were simultaneously DENV positive and two CHIKV-positive samples were simultaneously MAYV positive, at titers of 1:40 to 1:160. This suggested cross-reactive antibodies against heterologous alphaviruses and flaviviruses in 24% of ZIKV-positive/CHIKV-positive sera. In sum, low seroprevalence, invariably low antibody titers, and the distribution of positive specimens call into question the capability of ZIKV and CHIKV to infect New World NHP and establish sylvatic transmission cycles. IMPORTANCE Since 2013, Zika virus (ZIKV) and chikungunya virus (CHIKV) have infected millions of people in the Americas via urban transmission cycles. Nonhuman primates (NHP) are involved in sylvatic transmission cycles maintaining ZIKV and CHIKV in the Old World. We tested NHP sampled during 2012 to 2017 in urban and peri-urban areas severely affected by ZIKV and CHIKV in Brazil. Seroprevalence and antibody titers were low for both viruses. Additionally, we found evidence for infection by heterologous viruses eliciting cross-reactive antibodies. Our data suggest that urban or peri-urban NHP are not easily infected by ZIKV and CHIKV despite intense local transmission. These data may imply that the ZIKV and CHIKV outbreaks in the Americas cannot be sustained in urban or peri-urban NHP once human population immunity limits urban transmission cycles. Investigation of diverse animals is urgently required to determine the fate of the ZIKV and CHIKV outbreaks in the Americas.