Distinct roles for Argonaute proteins in small RNA-directed RNA cleavage pathways

Arthropod-borne viruses (arboviruses) transmitted by mosquito vectors cause many important emerging or resurging infectious diseases in humans including dengue, chikungunya and Zika. Understanding the co-evolutionary processes among viruses and vectors is essential for the development of novel transmission-blocking strategies. Episomal viral DNA fragments are produced from arboviral RNA upon infection of mosquito cells and adults. Additionally, sequences from insect-specific viruses and arboviruses have been found integrated into mosquito genomes. We used a bioinformatic approach to analyse the presence, abundance, distribution, and transcriptional activity of integrations from 425 non-retroviral viruses, including 133 arboviruses, across the presently available 22 mosquito genome sequences. Large differences in abundance and types of viral integrations were observed in mosquito species from the same region. Viral integrations are unexpectedly abundant in the arboviral vector species Aedes aegypti and Ae. albopictus, in which they are approximately ~10-fold more abundant than in other mosquito species analysed. Additionally, viral integrations are enriched in piRNA clusters of both the Ae. aegypti and Ae. albopictus genomes and, accordingly, they express piRNAs, but not siRNAs. Differences in the number of viral integrations in the genomes of mosquito species from the same geographic area support the conclusion that integrations of viral sequences is not dependent on viral exposure, but that lineage-specific interactions exist. Viral integrations are abundant in Ae. aegypti and Ae. albopictus, and represent a thus far underappreciated component of their genomes. Additionally, the genome locations of viral integrations and their production of piRNAs indicate a functional link between viral integrations and the piRNA pathway. These results greatly expand the breadth and complexity of small RNA-mediated regulation and suggest a role for viral integrations in antiviral defense in these two mosquito species.

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Comparative genomics shows that viral integrations are abundant and express piRNAs in the arboviral vectors Aedes aegypti and Aedes albopictus

Oropouche fever is an emerging zoonotic disease caused by Oropouche virus (OROV), an arthropod transmitted Orthobunyavirus circulating in South and Central America. During the last 60 years, more than 30 epidemics and over half a million clinical cases attributed to OROV infection have been reported in Brazil, Peru, Panama, Trinidad and Tobago. OROV fever is considered the second most frequent arboviral febrile disease in Brazil after dengue fever. OROV is transmitted through both urban and sylvatic transmission cycles, with the primary vector in the urban cycle being the anthropophilic biting midge Culicoides paraensis. Currently, there is no evidence of direct human-to-human OROV transmission. OROV fever is usually either undiagnosed due to its mild, self-limited manifestations or misdiagnosed because its clinical characteristics are similar to dengue, chikungunya, Zika and yellow fever, including malaria as well. At present, there is no specific antiviral treatment, and in the absence of a vaccine for effective prophylaxis of human populations in endemic areas, the disease prevention relies solely on vector control strategies and personal protection measures. OROV fever is considered to have the potential to spread across the American continent and under favorable climatic conditions may expand its geographic distribution to other continents. In view of OROV’s emergence, increased interest for formerly neglected tropical diseases and within the One Health concept, the existing knowledge and gaps of knowledge on OROV fever are reviewed.

Oropouche Fever: A Review.

Culex quinquefasciatus is the principal vector of bancroftian filariasis and a potential vector of Dirofilaria immitis. This mosquito species is also a potential vector of several arboviruses like West Nile virus (WNV), Rift Valley fever virus, avian pox and protozoa like Plasmodium relictum that causes bird malaria. This species has the ability to transmit other nematodes like Saurofilaria sp., Oswaldofilaria sp. In the USA, it is a potential vector of St. Louis encephalitis virus (SLEV). Japanese encephalitis virus (JEV) has been isolated from this mosquito in several occasions in Asia. Furthermore, it can transmit several other arboviruses in the laboratory conditions. This article is an attempt to review the bio-ecology, medical and veterinary importance of Culex quinquefasciatus. It acts as an important “urban bridge vector” which bridges different reservoir/amplifier hosts to humans because of its encounter with different vertebrates. Culex quinquefasciatus also creates an ecological bridge between urban, periurban and rural areas owing to its presence and adaptability in diverse ecological niches. Culex quinquefasciatus emerged as a smart vector because of the adaptive fitness, ecological plasticity, invasive behaviour, host specificity and high reproductive potential along with expanded immune gene repertoire property at the genetic level. This mosquito possesses the necessary potential to initiate and facilitate the disease transmission by establishing an effective vector-host transmission cyclernfor diverse pathogens in different environments. Thus, in the changing ecological conditions this mosquito might enhance its epidemiological importance in the near future as a smart vector for those pathogens which were isolated from this mosquito species but are presently not having any public health importance.

https://www.entomoljournal.com/archives/2016/vol4issue2/PartB/4-2-32.pdf

The Southern House Mosquito, Culex quinquefasciatus: profile of a smart vector

Recently, the environmental economist J.M. Salles (Salles, ) declared that “the Asian hornet was likely to be the most threatening invader insect in France.” Thirteen years after the accidental introduction in France, the Asian hornet (Vespa velutina nigrithorax) has invaded most west European countries. Little has been done to date to limit its progression and its economic, ecological and social impact. Although it is illusory to try to eradicate this species, it is known that a targeted control would limit its threatening trend. Current V. velutina control in France is mainly based on (i) high scale volunteer trapping by citizens and (ii) volunteer spotting of the nest. Evaluation of trapping strategies developed so far to control V. velutina expansion has highlighted their failure and has demonstrated the need to optimize nest detection techniques and to investigate on new control strategies. This review describes most of the means aimed to control predation and expansion of V. velutina, whether they have been scientifically assessed or only tested on field with decent success. Published prospective control methods and biological control techniques are also presented.

Options for the biological and physical control of Vespa velutina nigrithorax (Hym.: Vespidae) in Europe: A review

The maintenance of Japanese Encephalitis Virus (JEV) in nature occurs in a cycle which includes mosquito vectors and the vertebrate hosts. Japanese encephalitis (JE) being primarily a zoonotic disease, animal hosts such as pigs and birds play an important role in the maintenance and amplification of the virus. JE antibody has been detected in several poikilothermic and homeothermic vertebrates, apart from the recognized reservoir/amplifying hosts. Emerging arboviral diseases such as Japanese Encephalitis, Chikungunya, Dengue generally stems from an animal reservoir, but there is inadequate information on the natural history of arboviruses especially its method of survival in the inter- epidemic period. Keeping in view the above perspective, an attempt has been made to review the various non-human vertebrates infected with JEV and to analyze their epidemiological significance. Some zoonotic potential might exist in the ectothermic animals as overwintering reservoir hosts for Japanese Encephalitis Virus (JEV). Mosquito species having predilection to animal blood could get the virus from a broad array of low viraemic ectothermic and endothermic vertebrates, but possibly fail to attain the infective stage and to acquire transmission competence due to inadequate titre level and short duration of viraemia in those vertebrates. These animals might have some complementary role in the maintenance of the enzootic cycle of the virus along with the recognized principal reservoir hosts i.e., pigs and birds. The principal and complementary vertebrate reservoir hosts keep the virus circulating perennially in nature and epizootic occurs at the time of higher than average level of virus circulation.

https://www.faunajournal.com/vol1Issue6/Issue_oct_2014/1-6-9.1.pdf

Japanese Encephalitis Virus (JEV) infection in different vertebrates and its epidemiological significance: a Review

SARS-CoV-2 is a new form of β-coronavirus that has been recently discovered and is responsible for COVID 19 pandemic. The earliest infection can be traced back to Wuhan, China. From there it has spread all over the world. Keeping in view the above perspective, an attempt is made in order to find out the epidemiological pattern of COVID 19 pandemic, if any, in different geo-climatological regions of the world in terms of case incidence and mortality. This study is also an endeavor to review and analyze the gradual changes of the genetic makeup of SARS-CoV from evolutionary and epidemiological perspectives. The raw data of COVID-19 cases and death incidences were collected from the World Health Organization (WHO) website from the time period: 1st April to 6th April, 2020. The data that are utilized here for general and Case fatality rate (CFR) based analysis. Western pacific region, European region and Americas have the greatest number of infected cases (P < 0.001); whereas deaths have been found to be significantly higher in Europe (P < 0.001). Total number of confirmed cases and deaths in south-east Asia are comparatively lower (P < 0.001). Case fatality rate (CFR) has also found significant for European region. SARS-CoV-2 is considered to be a strain of SARS-CoV that has a high rate of pathogenicity and transmissibility. Result indicated that the European region has been affected mostly for both cases and death incidences. The novel mutations in SARS-CoV-2 possibly increase the virus infectivity. Genetic heterogeneity of this virus within the human population might originate as the representatives of naturally selected virus quasispecies. In this context, the presence of the asymptomatic individuals could be a significant concern for SARS-CoV-2 epidemiology. Further studies are required to understand its genetic evolution and epidemiological significance.

Changing epidemiology of SARS-CoV in the context of COVID-19 pandemic.

SARS-CoV2 is a new form of β‐coronavirus that has been recently discovered and is responsible for COVID 19 pandemic. The earliest infection can be traced back to Wuhan, China. From there it has spread all over the world. It is considered to have a zoonotic origin in bats and has resulted in human to human transmission. SARS-CoV2 is considered to be a strain of SARS-CoV that has a high rate of pathogenicity and transmissibility. It has been documented that the total number of confirmed cases and deaths in Europe is comparatively significant than other parts of the world. Thus, keeping in view the above perspective, an attempt is made in order to find out the epidemiological pattern of COVID 19 pandemic, if any, in different geo-climatological regions of the world in terms of case incidence and mortality. This study is also an endeavor to review and analyze the gradual changes of the genetic makeup of SARS CoV from evolutionary and epidemiological perspectives.

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Changing Epidemiology of SARS-CoV in the Context of COVID-19 Pandemic

The recent outbreak of the novel Corona virus (SARS-CoV-2), that has taken the world by storm, is a disturbing case of severity posed by a highly dynamic viral strain. Suspected to have originated from bats, a reservoir host of many deadly viral diseases, the COVID-19 pandemic might be an alarming but a substantially preliminary instance of a much complexly evolving future of disease epidemiology, at the interface of rapid and robust genetic recombination, mutation and highly adaptable strains of the Coronaviridae family. Keeping these attributes in mind, the idea of host(s) as “mixing pot” is introduced through this review to capture the plausible future of the Corona virus dynamics through a vector-borne transmission.

Sajal Bhattacharya

Papers

The Southern House Mosquito, Culex quinquefasciatus: profile of a smart vector

Japanese Encephalitis Virus (JEV) infection in different vertebrates and its epidemiological significance: a Review

Changing epidemiology of SARS-CoV in the context of COVID-19 pandemic.

Changing Epidemiology of SARS-CoV in the Context of COVID-19 Pandemic

COULD NOVEL CORONA VIRUS (SARS-CoV-2) BE THE EVOLVING FACE OF A NEWGENERATION OF GENETICALLY COMPLEX EPIDEMIOLOGICAL CHALLENGE?