Biology subjects

Louie, W.

Publications and source records attributed to Louie, W..

4 recordsLinked to original sources

bioRxiv2025

Rhesus macaques model human Mayaro virus disease and transmit to Aedes aegypti mosquitoes

BackgroundMayaro virus (MAYV) is a mosquito-borne alphavirus endemic to Latin America that causes fever and arthritis. Unlike the related chikungunya virus, MAYV has not caused widespread, human-amplified epidemics. One possible explanation is that human viremia levels are too low to support transmission to urban Aedes (Stegomyia) aegypti mosquitoes. We used rhesus macaques (RM) to model human-to-Ae. aegypti transmission and to further expand understanding of their relevance to human MAYV disease. Methodology/Principal FindingsTwelve RM were inoculated with a genotype D lineage MAYV strain using one of 3 doses: 7 log10 plaque forming units (PFU) intravenously (IV), 7 log10 PFU subcutaneously (SC), or 3 log10 PFU SC. Viremia was measured daily in plasma and RM were euthanized 10- or 12-days post-inoculation (dpi). On 2, 3, 5, and 7 dpi, Ae. aegypti were allowed to bloodfeed, incubated for 10 days, then dissected and tested to detect MAYV in tissues and saliva. RM developed infectious MAYV viremias lasting 3 days, peaking 1-2 dpi with titers ranging from 2-6 log10 PFU/ml. RM inoculated with 7 log10 PFU IV developed significantly higher viremias (area under the curve) than those receiving 3 log10 PFU SC. MAYV RNA was detected in muscle, lymphoid, central nervous, and cardiac tissues. RM showed no signs of fever or joint swelling but some developed mild rashes in areas distant from mosquito feeding sites and histologic inflammation was observed in joints and muscles. Only Ae. aegypti that fed on viremic RM 2 dpi became infected, with an overall infection rate of 48%. Among all mosquitoes that fed on RM 2 dpi, only 2% (4/217) had infectious MAYV in their saliva, suggesting transmission competence. Despite 11 of 12 RM transmitting MAYV to at least one mosquito, individual RM varied in infectiousness to Ae. aegypti, and mosquito cohort infection rates did not correlate with RM viremia levels. Conclusions/SignificanceRM exhibit short-lived MAYV viremias, broad tissue tropism, and mild joint and muscle inflammation, closely resembling human infection. While viremic RM can infect Ae. aegypti, the transmission window is narrow and transmission by Ae. aegypti is rare. The combination of a short infectious period in RM and low transmissibility of Ae. aegypti infected from RM may help explain the absence of widespread urban MAYV outbreaks. AUTHOR SUMMARYMayaro virus (MAYV) is a mosquito-borne virus found in Latin America that causes fever and joint pain, similar to chikungunya virus (CHIKV). However, unlike CHIKV, MAYV has not led to large outbreaks. One reason may be that levels of MAYV in human blood are too low for Aedes aegypti mosquitoes--known for spreading chikungunya, dengue, and Zika--to pick up and transmit the virus in cities. To better understand this, we studied rhesus macaques, a monkey species that serves as a model for how MAYV behaves in people. We tracked virus levels in their blood and tissues and observed mild joint and muscle inflammation, similar to Mayaro fever in people. Although the macaques were able to infect some Ae. aegypti mosquitoes, the transmission window was short, and only a few mosquitoes that became infected had virus in their saliva, suggesting transmission competence. This limited ability of urban mosquitoes to spread MAYV may help explain why major outbreaks have not occurred.

microbiology↗

bioRxiv2022

Microbes reduce susceptibility of Aedes aegypti to Zika virus by enhancing blood digestion and limiting midgut cell infection

The worldwide expansion of mosquito-borne pathogens necessitates improved control measures, including approaches to reduce transmission by mosquito vectors. Reducing transmission is challenging because determinants of vector competence for viruses like Zika (ZIKV) are poorly understood. Our previous work established that Aedes (Ae.) aegypti larvae reared in environmental water containing microbes are less susceptible to ZIKV as adults compared to cohorts reared in laboratory tap water with fewer microbial species and lower microbial abundance. Here, we identify a process by which environment-derived microbes reduce susceptibility of Ae. aegypti for ZIKV. Provided that the midgut represents the first barrier to mosquito infection, we hypothesized that microbial exposure modulates midgut infection by ZIKV. Since mosquitoes live in water as larvae and pupae and then transition to air as adults, we also define the stage in the life of a mosquito when microbial exposure reduces ZIKV susceptibility. Ae. aegypti larvae were reared in water containing microbes and then treated with antibiotics during the pupal and adult stages, adult stage only, or provided no antibiotics at any stage. Vector competence was next evaluated in mosquitoes that ingested ZIKV-spiked bloodmeals. Antibiotic treated mosquitoes with reduced microbiota showed enhanced ZIKV infection rates in Ae. aegypti treated as both pupae and adults. Antibiotic treatment to disrupt microbes in pupal and adult mosquitoes also resulted in increased midgut epithelium permeability, higher numbers of ZIKV-infected midgut cells, and impaired bloodmeal digestion. Parallel control experiments with antibiotic-treated or gnotobiotic mosquitoes reared in laboratory water showed that the dysbiotic state created by antibiotic use does not influence ZIKV vector competence or midgut permeability and that more than the bacterial species in gnotobiotic mosquitoes is responsible for reducing ZIKV vector competence. Ae. aegypti with disrupted microbiota via antibiotic treatment as pupae and adults that ingested ZIKV in bloodmeals showed reduced expression of genes associated with bloodmeal digestion and metabolism relative to mosquitoes whose microbes were not reduced with antibiotics. Together, these data show that exposure to microbes throughout the life of Ae. aegypti restricts ZIKV infection by facilitating blood digestion and reducing midgut cell infection. Understanding the connections between mosquito microbiota, midgut physiology, and arbovirus susceptibility can lead to novel approaches to decrease mosquito transmission and will improve understanding of vector competence in environmental habitats containing microbes. Author SummaryMosquito-transmitted viruses like Zika continue to threaten human health. Absent vaccines or treatments, controlling mosquitoes or limiting their ability to transmit viruses represents a primary way to prevent mosquito-borne viral diseases. The role mosquito microbiota play in shaping transmission of Zika virus has been limited to association-based studies. Our prior work showed that Aedes aegypti mosquito larvae that develop in water containing bacteria are less susceptible to Zika virus compared to larvae reared in laboratory tap water with fewer numbers and species of bacteria. Here we identify a process that explains this association. Since mosquitoes are aquatic as larvae and pupae and terrestrial as adults, we also define the life stage when microbes need be present to reduce Zika virus susceptibility. We used antibiotics to reduce environmental water-derived microbes at pupal and adult or only adult stages and observed that microbial disruption via antibiotic treatment increases Zika virus infection and midgut permeability and impairs bloodmeal digestion. These findings advance understanding of microbiota-mosquito-virus interactions and further implicate microbes as a means to restrict virus infection of mosquitoes.

microbiology↗

bioRxiv2021

Microbial composition in larval water enhances Aedes aegypti development but reduces transmissibility of Zika virus

Arthropod-borne viral (arboviral) pathogens comprise a significant global disease burden, and outbreaks are expected to increase as vectors expand. Surveillance and mitigation of arboviruses like Zika virus (ZIKV) require accurate estimates of transmissibility by vector mosquitoes. While numerous laboratory vector competence experiments show that Aedes spp. mosquitoes are competent ZIKV vectors, differences in experimental protocols prevent direct comparisons of relative transmissibility across studies. An understudied factor complicating these comparisons is differential environmental microbiota exposures, where most vector competence studies use mosquitoes reared in laboratory tap water, which does not represent the microbial complexity of environmental water where wild larvae develop. We simulated natural larval development by rearing Californian Aedes aegypti with microbes obtained from cemetery headstone water, a common larval habitat in California, compared to conventional laboratory tap water. Ae. aegypti larvae reared in environmental cemetery water pupated 3 days faster and at higher rates. Female adult mosquitoes reared in environmental water were less competent vectors of ZIKV compared to laboratory water-reared Ae. aegypti, as evidenced by significantly reduced infection and transmission rates for two 2015 ZIKV strains and in two Ae. aegypti colonies from California. Microbiome comparisons of laboratory- and environment-water reared mosquitoes as well as their rearing water showed significantly higher bacterial diversity in environment water; despite this pattern, corresponding differences in diversity were not consistently detected in adult mosquitoes reared in different water sources. We also detected more significant associations between the microbial composition of adult mosquitoes and whether they ingested a bloodmeal than larval water type. Together, these results highlight the role of transient microbes in the larval environment in modulating vector competence. Laboratory vector competence likely overestimates true transmissibility of arboviruses like ZIKV when conventional laboratory water is used for rearing. ImportanceWe observed that Ae. aegypti mosquitoes reared in water from cemetery headstones instead of the laboratory tap exhibited a reduced capacity to become infected with and transmit Zika virus. Water from the environment contained more bacterial species than tap water, but these bacteria were not consistently detected in adult mosquitoes. Our results suggest that rearing mosquito larvae in water collected from local environments as opposed to laboratory tap water, as is conventional, provides a more realistic assessment of vector competence since it better recapitulates the natural environment in which larvae develop. Given that laboratory vector competence is used to define the species to target for control, use of environmental water to rear larvae could better approximate the microbial exposures of wild mosquitoes, lessening the potential for overestimating transmission risk.

microbiology↗

bioRxiv2020

Two sides of a coin: a Zika virus mutation selected in pregnant rhesus macaques promotes fetal infection in mice but at a cost of reduced fitness in nonpregnant macaques and diminished transmissibility by vectors

Although fetal death is now understood to be a severe outcome of congenital Zika syndrome, the role of viral genetics is still unclear. We sequenced Zika virus (ZIKV) from a rhesus macaque fetus that died after inoculation and identified a single intra-host mutation, M1404I, in the ZIKV polyprotein, located in NS2B. Targeted sequencing flanking position 1404 in 9 additional macaque mothers and their fetuses identified M1404I at sub-consensus frequency in the majority (5 of 9, 56%) of animals and some of their fetuses. Despite its repeated presence in pregnant macaques, M1404I occurs rarely in humans since 2015. Since the primary ZIKV transmission cycle is human-mosquito-human, mutations in one host must be retained in the alternate host to be perpetuated. We hypothesized that ZIKV I1404 increases fitness in non-pregnant macaques and pregnant mice but is less efficiently transmitted by vectors, explaining its low frequency in humans during outbreaks. By examining competitive fitness relative to M1404, we observed that I1404 produced lower viremias in non-pregnant macaques and was a weaker competitor in tissues. In pregnant wildtype mice ZIKV I1404 increased the magnitude and rate of placental infection and conferred fetal infection, contrasting with M1404, which was not detected in fetuses. Although infection and dissemination rates were not different, Ae. aegypti transmitted ZIKV I1404 more poorly than M1404. Our data highlight the complexity of arbovirus mutation-fitness dynamics, and suggest that intrahost ZIKV mutations capable of augmenting fitness in pregnant vertebrates may not necessarily spread efficiently via mosquitoes during epidemics. IMPORTANCEAlthough Zika virus infection of pregnant women can result in congenital Zika syndrome, the factors that cause the syndrome in some but not all infected mothers are still unclear. We identified a mutation that was present in some ZIKV genomes in experimentally inoculated pregnant rhesus macaques and their fetuses. Although we did not find an association between the presence of the mutation and fetal death, we performed additional studies with it in non-pregnant macaques, pregnant mice, and mosquitoes. We observed that the mutation increased the ability of the virus to infect mouse fetuses but decreased its capacity to produce high levels of virus in the blood of non-pregnant macaques and to be transmitted by mosquitoes. This study shows that mutations in mosquito-borne viruses like ZIKV that increase fitness in pregnant vertebrates may not spread in outbreaks when they compromise transmission via mosquitoes and fitness in non-pregnant hosts.

microbiology↗