RESUMO
Flaviviruses, such as Zika virus, yellow fever virus, dengue virus, and West Nile virus (WNV), are a serious concern for human health. Flaviviruses produce an abundant noncoding subgenomic flavivirus RNA (sfRNA) in infected cells. sfRNA results from stalling of the host 5'-3' exoribonuclease XRN1/Pacman on conserved RNA structures in the 3' untranslated region (UTR) of the viral genomic RNA. sfRNA production is conserved in insect-specific, mosquito-borne, and tick-borne flaviviruses and flaviviruses with no known vector, suggesting a pivotal role for sfRNA in the flavivirus life cycle. Here, we investigated the function of sfRNA during WNV infection of Culex pipiens mosquitoes and evaluated its role in determining vector competence. An sfRNA1-deficient WNV was generated that displayed growth kinetics similar to those of wild-type WNV in both RNA interference (RNAi)-competent and -compromised mosquito cell lines. Small-RNA deep sequencing of WNV-infected mosquitoes indicated an active small interfering RNA (siRNA)-based antiviral response for both the wild-type and sfRNA1-deficient viruses. Additionally, we provide the first evidence that sfRNA is an RNAi substrate in vivo Two reproducible small-RNA hot spots within the 3' UTR/sfRNA of the wild-type virus mapped to RNA stem-loops SL-III and 3' SL, which stick out of the three-dimensional (3D) sfRNA structure model. Importantly, we demonstrate that sfRNA-deficient WNV displays significantly decreased infection and transmission rates in vivo when administered via the blood meal. Finally, we show that transmission and infection rates are not affected by sfRNA after intrathoracic injection, thereby identifying sfRNA as a key driver to overcome the mosquito midgut infection barrier. This is the first report to describe a key biological function of sfRNA for flavivirus infection of the arthropod vector, providing an explanation for the strict conservation of sfRNA production. IMPORTANCE: Understanding the flavivirus transmission cycle is important to identify novel targets to interfere with disease and to aid development of virus control strategies. Flaviviruses produce an abundant noncoding viral RNA called sfRNA in both arthropod and mammalian cells. To evaluate the role of sfRNA in flavivirus transmission, we infected mosquitoes with the flavivirus West Nile virus and an sfRNA-deficient mutant West Nile virus. We demonstrate that sfRNA determines the infection and transmission rates of West Nile virus in Culex pipiens mosquitoes. Comparison of infection via the blood meal versus intrathoracic injection, which bypasses the midgut, revealed that sfRNA is important to overcome the mosquito midgut barrier. We also show that sfRNA is processed by the antiviral RNA interference machinery in mosquitoes. This is the first report to describe a pivotal biological function of sfRNA in arthropods. The results explain why sfRNA production is evolutionarily conserved.
Assuntos
Culex/virologia , Culicidae/genética , Flavivirus/genética , Interferência de RNA/fisiologia , RNA Viral/genética , Febre do Nilo Ocidental/transmissão , Vírus do Nilo Ocidental/genética , Regiões 3' não Traduzidas/genética , Animais , Linhagem Celular , Chlorocebus aethiops , Culex/genética , Culicidae/virologia , Vírus da Dengue/genética , Insetos Vetores/genética , RNA Interferente Pequeno/genética , Células Vero , Febre do Nilo Ocidental/virologia , Vírus da Febre Amarela/genética , Zika virus/genética , Infecção por Zika virus/transmissão , Infecção por Zika virus/virologiaRESUMO
After an introduction of the concept of 'filaria', the different forms of filaria parasitic on man are briefly summed up. The morphological and physiological characteristics of W. bancrofti are discussed, and the symptoms caused by this worm. After pointing out the necessity for the population of Paramaribo to submit themselves to an examination of filaria, the organization of the department for the prevention of filaria is briefly described and the results of the examination of 50.861 inhabitants. It appeared that 24.2 per cent of the examined population of Paramaribo is infected with W. bancrofti; besides, it was observed that the blood of 88.2 per cent of the sufferers from elephantiasis contained no microfilariaemie; possible explanations are given for this latter phenomenon. The Creole population group appears to be most strongly infected. The results of the polyclinical treatment with Hetrazan are stated, namely, a disappearance and long absence of the microfilariaemie. Other sanitary measures are also stated. Finally the presence of F. ozzardi and A. perstans in the blood of the Amerindians living in the savannah zone is referred to.(AU)
Assuntos
Resumo em Inglês , Filariose , Wuchereria bancrofti , Elefantíase , Mansonella , Mansonella , SurinameRESUMO
The possible causes of an acute filaria attack are discussed, and case histories are given. Acute lymphadenitis is one of the clinical manifestations of the infection with W. bancrofti. In one case an acute attack occurred during treatment with hetrazan, which histopathologically must have been the result of the death of a macrofilaria. An acute filaria attack is described, which must have been due to dissemination of microfilariae; the outlet from the lymphatic gland had evidently been obstructed. However, the cause of lymphadenopathy (acute lymphadenitis) has not been explained, not even by the so-called allergic reaction
