Understanding Of Virus Transmission Research Articles

Increased blood meal size and feeding frequency compromise Aedes aegypti midgut integrity and enhance dengue virus dissemination.

Aedes aegypti is a highly efficient vector for numerous pathogenic arboviruses including dengue virus (DENV), Zika virus, and yellow fever virus. This efficiency can in part be attributed to their frequent feeding behavior. We previously found that acquisition of a second, full, non-infectious blood meal could accelerate virus dissemination within the mosquito by temporarily compromising midgut basal lamina integrity; however, in the wild, mosquitoes are often interrupted during feeding and only acquire partial or minimal blood meals. To explore the impact of this feeding behavior further, we examined the effects of partial blood feeding on DENV dissemination rates and midgut basal lamina damage in Ae. aegypti. DENV-infected mosquitoes given a secondary partial blood meal had intermediate rates of dissemination and midgut basal lamina damage compared to single-fed and fully double-fed counterparts. Subsequently, we evaluated if basal lamina damage accumulated across feeding episodes. Interestingly, within 24 hours of feeding, damage was proportional to the number of blood meals imbibed; however, this additive effect returned to baseline levels by 96 hours. These data reveal that midgut basal lamina damage and rates of dissemination are proportional to feeding frequency and size, and further demonstrate the impact that mosquito feeding behavior has on vector competence and arbovirus epidemiology. This work has strong implications for our understanding of virus transmission in the field and will be useful when designing laboratory experiments and creating more accurate models of virus spread and maintenance.

Immunofluorescent Labeling of Plant Virus and Insect Vector Proteins in Hemipteran Guts.

Most plant viruses in nature are transmitted from one plant to another by hemipteran insects. A high population density of the vector insects that are highly efficient at virus transmission plays a key role in virus epidemics in fields. Studying virus-insect vector interactions can advance our understanding of virus transmission and epidemics with the aim of designing novel strategies to control plant viruses and their vector insects. Immunofluorescence labeling has been widely used to analyze interactions between pathogens and hosts and is used here in the white-backed planthopper (WBPH, Sogatella furcifera), which efficiently transmits the southern rice black streaked dwarf virus (SRBSDV, genus Fijivirus, family Reoviridae), to locate the virions and insect proteins in the midgut epithelial cells. Using laser scanning confocal microscopy, we studied the morphological characteristics of midgut epithelial cells, cellular localization of insect proteins, and the colocalization of virions and an insect protein. This protocol can be used to study virus activities in insects, functions of insect proteins, and interactions between virus and vector insect.

American Neurogastroenterology and Motility Society Task Force Recommendations for Resumption of Motility Laboratory Operations During the COVID-19 Pandemic.

The American Neurogastroenterology and Motility Society Task Force recommends that gastrointestinal motility procedures should be performed in motility laboratories adhering to the strict recommendations and personal protective equipment (PPE) measures to protect patients, ancillary staff, and motility allied health professionals. When available and within constraints of institutional guidelines, it is preferable for patients scheduled for motility procedures to complete a coronavirus disease 2019 (COVID-19) test within 48 hours before their procedure, similar to the recommendations before endoscopy made by gastroenterology societies. COVID-19 test results must be documented before performing procedures. If procedures are to be performed without a COVID-19 test, full PPE use is recommended, along with all social distancing and infection control measures. Because patients with suspected motility disorders may require multiple procedures, sequential scheduling of procedures should be considered to minimize need for repeat COVID-19 testing. The strategies for and timing of procedure(s) should be adapted, taking into consideration local institutional standards, with the provision for screening without testing in low prevalence areas. If tested positive for COVID-19, subsequent negative testing may be required before scheduling a motility procedure (timing is variable). Specific recommendations for each motility procedure including triaging, indications, PPE use, and alternatives to motility procedures are detailed in the document. These recommendations may evolve as understanding of virus transmission and prevalence of COVID-19 infection in the community changes over the upcoming months.

Identifying airborne transmission as the dominant route for the spread of COVID-19

Various mitigation measures have been implemented to fight the coronavirus disease 2019 (COVID-19) pandemic, including widely adopted social distancing and mandated face covering. However, assessing the effectiveness of those intervention practices hinges on the understanding of virus transmission, which remains uncertain. Here we show that airborne transmission is highly virulent and represents the dominant route to spread the disease. By analyzing the trend and mitigation measures in Wuhan, China, Italy, and New York City, from January 23 to May 9, 2020, we illustrate that the impacts of mitigation measures are discernable from the trends of the pandemic. Our analysis reveals that the difference with and without mandated face covering represents the determinant in shaping the pandemic trends in the three epicenters. This protective measure alone significantly reduced the number of infections, that is, by over 78,000 in Italy from April 6 to May 9 and over 66,000 in New York City from April 17 to May 9. Other mitigation measures, such as social distancing implemented in the United States, are insufficient by themselves in protecting the public. We conclude that wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with simultaneous social distancing, quarantine, and contact tracing, represents the most likely fighting opportunity to stop the COVID-19 pandemic. Our work also highlights the fact that sound science is essential in decision-making for the current and future public health pandemics.

Green Bees: Reverse Genetic Analysis of Deformed Wing Virus Transmission, Replication, and Tropism.

Environmental and agricultural pollination services by honey bees, Apis mellifera, and honey production are compromised by high levels of annual colony losses globally. The majority are associated with disease caused by deformed wing virus (DWV), a positive-strand RNA virus, exacerbated by the ectoparasitic mite Varroa destructor. To improve honey bee health, a better understanding of virus transmission and pathogenesis is needed which requires the development of tools to study virus replication, transmission, and localisation. We report the use of reverse genetic (RG) systems for the predominant genetically distinct variants of DWV to address these questions. All RG-recovered viruses replicate within 24 h post-inoculation of pupae and could recapitulate the characteristic symptoms of DWV disease upon eclosion. Larvae were significantly less susceptible but could be infected orally and subsequently developed disease. Using genetically tagged RG DWV and an in vitro Varroa feeding system, we demonstrate virus replication in the mite by accumulation of tagged negative-strand viral replication intermediates. We additionally apply a modified DWV genome expressing a fluorescent reporter protein for direct in vivo observation of virus distribution in injected pupae or fed larvae. Using this, we demonstrate extensive sites of virus replication in a range of pupal tissues and organs and in the nascent wing buds in larvae fed high levels of virus, indicative of a direct association between virus replication and pathogenesis. These studies provide insights into virus replication kinetics, tropism, transmission, and pathogenesis, and produce new tools to help develop the understanding needed to control DWV-mediated colony losses.

Surveillance for Heartland Virus (Bunyaviridae: Phlebovirus) in Missouri During 2013: First Detection of Virus in Adults of Amblyomma americanum (Acari: Ixodidae).

During 2013, we collected and tested ticks for Heartland virus (HRTV), a recently described human pathogen in the genus Phlebovirus (Bunyaviridae), from six sites in northwestern Missouri. Five sites were properties owned by HRTV patients, and the sixth was a conservation area that yielded virus in ticks during 2012. We collected 39,096 ticks representing five species; however, two species, Amblyomma americanum (L.) (97.6%) and Dermacentor variabilis (Say) (2.3%), accounted for nearly all ticks collected. We detected 60 HRTV-positive tick pools and all were composed of A americanum: 53 pools of nymphs, six pools of male adults, and one pool of female adults. This is the first record of HRTV in adult ticks. Virus was detected at five properties that yielded A. americanum ticks, including properties owned by four of five patients. Virus was detected at two sites that yielded virus in 2012. Detection of virus in multiple years indicates that the virus persists in ticks within a relatively small geographic area, although infection rates (IR) may vary greatly among sites and between years at a site. IR per 1,000 A. americanum in northwestern Missouri during the April-July 2013 study period were as follows: all adults, IR = 1.13; adult females, IR = 0.33; adult males, IR = 1.90; and nymphs, IR = 1.79. The IR in nymphs, the stage with the largest data set, corresponds to 1/559 infected ticks. Having robust estimates of IR in various stages for A. americanum should lead to more accurate public health messaging and a better understanding of virus transmission.

Arthropod Transmission of Plant Viruses: a New Synthesis

This review focuses on the more important arthropod vectors of plant viruses, 4 families of homopterans (aphids, whiteflies, leafhoppers, and delphacid planthoppers), thrips, chrysomellid beetles, and, among the acarines, the eriophyid mites. More than 380 viruses from 27 plant virus genera are transmitted by the Homoptera. Two systems of terminology have been devised to describe and group homopteran-borne plant viruses. One is based on persistence of transmissible virus in the vector and the other on the mechanism of transmission or route of virus transport in the vector. Here the 2 systems are combined to create the following 4 transmission groups: (1) the nonpersistently transmitted, stylet-borne viruses; (2) the semi-persistently transmitted, foregut-borne viruses; (3) the persistently transmitted, circulative viruses; and (4) the persistently transmitted, propagative viruses. Homopteran transmitted viruses are characterized by the following 3 traits: (1) no virus is transmitted by vectors from >1 homopteran family; (2) most plant virus genera have vectors from 1 family of homopterans, although some are characterized by vectors from ≥2 families, usually from the same homopteran suborder; (3) the persistence and mode of transmission for all viruses within a virus genus is almost always the same and appears to be a stable evolutionary trait. Certain aspects of the feeding behavior and the morphology of the mouth parts and digestive systems of the Homoptera and other vectors covered in this review are discussed with respect to their relevance to vector transmission. The thrips-borne viruses are transmitted much in the same way as are the persistently transmitted, propagative viruses by the Homoptera. At least 42 plant viruses are transmitted by the Coleoptera. Their mode of transmission differs markedly from that described for the homopterans and thrips. So, too, does the transmission of plant viruses by eriophyid mites. Throughout this review, frequent mention is made as to how an understanding of virus transmission is important to interpreting virus epidemiology and in the control of virus disease.

Modelling the epizootiology of gypsy moth nuclear polyhedrosis virus

Abstract Qualitative understanding of the dynamics of epizootics of the nuclear polyhedrosis virus of gypsy moth has become complete enough to justify attempts to quantitatively predict the timing and intensity of epizootics within a season. In earlier work (Dwyer and Elkinton, 1993), we compared the predictions of a simple differential equation model derived from Anderson and May (1981) to time series of virus mortality in each of eight gypsy moth populations (Woods and Elkinton, 1987). The model's predictions were very accurate for high density populations, but seriously under-estimated virus mortality in low density populations. Here we compare the predictions of the simple model to those of the gypsy moth life system model (GMLSM, Sheehan, 1985; Colbert and Racin, 1991), a highly complex computer simulation of gypsy moth population dynamics and forest stand growth that incorporates much of the existing knowledge of the many factors influencing gypsy moth populations. In particular we looked at two different versions of the GMLSM that incorporate two different models of virus transmission. One was identical to that of the simple model (Anderson and May, 1981; Dwyer and Elkinton, 1993), in which the rate of transmission was a constant (the transmission coefficient) times the product of the densities of healthy larvae and the densities infectious virus particles on foliage. The other approach, developed by Valentine and Podgwaite (1982) was a detailed model of production and consumption of infective particles on foliage. The model took account of age-related changes in the amount of foliage consumed and the variation in susceptibility of larvae to virus (LD50). The Anderson and May version of the GMLSM performed about as well as the simple differential equation model, but only for values of the transmission coefficient about 250 times higher that those we had determined experimentally (Dwyer and Elkinton, 1993). The Valentine and Podgwaite (1982) version of the GMLSM gave a much better fit, but only for values of LD50 that were 100 times higher than those determined experimentally. Future research will focus on efforts to refine our understanding of virus transmission in order to explain and reduce the discrepancies between model predictions and observed mortality from virus in fieldpopulations.