Incorporation of CD55 into the Zika Viral Envelope Contributes to Its Stability against Human Complement.

The rapid spread of the virus in Latin America and the association of the infection with microcephaly in newborns or Guillain-Barré Syndrome in adults prompted the WHO to declare the Zika virus (ZIKV) epidemic to be an international public health emergency in 2016. As the virus was first discovered in monkeys and is spread not only by mosquitos but also from human to human, we investigated the stability to the human complement of ZIKV derived from mosquito (ZIKVInsect), monkey (ZIKVVero), or human cells (ZIKVA549 and ZIKVFibro), respectively. At a low serum concentration (10%), which refers to complement concentrations found on mucosal surfaces, the virus was relatively stable at 37 °C. At higher complement levels (up to 50% serum concentration), ZIKV titers differed significantly depending on the cell line used for the propagation of the virus. While the viral titer of ZIKVInsect decreased about two orders in magnitude, when incubated with human serum, the virus derived from human cells was more resistant to complement-mediated lysis (CML). By virus-capture assay and Western blots, the complement regulator protein CD55 was identified to be incorporated into the viral envelope. Blocking of CD55 by neutralizing Abs significantly increased the sensitivity to human complement. Taken together, these data indicate that the incorporation of CD55 from human cells contributes to the stability of ZIKV against complement-mediated virolysis.

Interference of the Zika Virus E-Protein With the Membrane Attack Complex of the Complement System.

The complement system has developed different strategies to clear infections by several effector mechanisms, such as opsonization, which supports phagocytosis, attracting immune cells by C3 and C5 cleavage products, or direct killing of pathogens by the formation of the membrane attack complex (MAC). As the Zika virus (ZIKV) activates the classical complement pathway and thus has to avoid clearance by the complement system, we analyzed putative viral escape mechanisms, which limit virolysis. We identified binding of the recombinant viral envelope E protein to components of the terminal pathway complement (C5b6, C7, C8, and C9) by ELISA. Western blot analyses revealed that ZIKV E protein interfered with the polymerization of C9, induced on cellular surfaces, either by purified terminal complement proteins or by normal human serum (NHS) as a source of the complement. Further, the hemolytic activity of NHS was significantly reduced in the presence of the recombinant E protein or entire viral particles. This data indicates that ZIKV reduces MAC formation and complement-mediated lysis by binding terminal complement proteins to the viral E protein.

Demographic and seasonal characteristics of respiratory pathogens in neonates and infants aged 0 to 12 months in the Central-East region of Tunisia.

BACKGROUND: This study aimed to characterize the epidemiology of pathogenic respiratory agents in patients aged 0 to 12 months and hospitalized for acute respiratory infections in Tunisia between 2013 and 2014. METHODS: A total of 20 pathogens, including viruses, Mycoplasma pneumoniae, and Streptococcus pneumoniae, were detected using molecular sensitive assays, and their associations with the patient's demographic data and season were analyzed. RESULTS: Viral infectious agents were found in 449 (87.2%) of 515 specimens. Dual and multiple infectious agents were detected in 31.4% and 18.6% of the samples, respectively. Viral infection was predominant in the pediatric environment (90.8%, P < 0.001), male patients (88.0%), and spring (93.8%). Rhinovirus was the most detected virus (51.8%) followed by respiratory syncytial virus A/B (34.4%), coronavirus group (18.5%), adenovirus (17.9%), and parainfluenza viruses 1-4 (10.9%). Respiratory Syncytial virus A/B was significantly associated with gender (38.0% male cases vs 28.3% female cases, P = 0.02). Infections by Adenovirus, Bocavirus, and Metapneumovirus A/B increased with increasing age of patients (predominated cases aged 6-12 months, P < 0.001). S. pneumoniae was detected in 30.9% of th tested samples. In 18.2% of the negative viral infections, only S. pneumoniae was identified. CONCLUSION: A predominance of the rhinovirus infection was observed in this study. Coronavirus subtypes were described for the first time in Tunisia. The observed different pathogenic profiles across age groups could be helpful to avoid the misclassification of patients presenting with ARIs at the triage level when no standardized protocol is available. This study will provide clues for physicians informing decisions regarding preventive strategies and medication in Tunisia.

Active Human Complement Reduces the Zika Virus Load via Formation of the Membrane-Attack Complex.

Although neglected in the past, the interest on Zika virus (ZIKV) raised dramatically in the last several years. The rapid spread of the virus in Latin America and the association of the infection with microcephaly in newborns or Guillain-Barré Syndrome in adults prompted the WHO to declare the ZIKV epidemic to be an international public health emergency in 2016. As the virus gained only limited attention in the past, investigations on interactions of ZIKV with human complement are limited. This prompted us to investigate the stability of the virus to human complement. At low serum concentrations (10%) which refers to complement concentrations found on mucosal surfaces, the virus was relatively stable at 37°C, while at high complement levels (50% serum concentration) ZIKV titers were dramatically reduced, although the virus remained infectious for about 4-5 min under these conditions. The classical pathway was identified as the main actor of complement activation driven by IgM antibodies. In addition, direct binding of C1q to both envelope and NS1 proteins was observed. Formation of the MAC on the viral surface and thus complement-mediated lysis and not opsonization seems to be essential for the reduction of viral titers.

Epidemiology and clinical profile of pathogens responsible for the hospitalization of children in Sousse area, Tunisia.

This study aimed to identify a broad spectrum of respiratory pathogens from hospitalized and not-preselected children with acute respiratory tract infections in the Farhat Hached University-hospital of Sousse, Tunisia. Between September 2013 and December 2014, samples from 372 children aged between 1 month and 5 years were collected, and tested using multiplex real-time RT-PCR by a commercial assay for 21 respiratory pathogens. In addition, samples were screened for the presence of Streptococcus pneumoniae 16S rDNA using real-time PCR. The viral distribution and its association with clinical symptoms were statistically analyzed. Viral pathogens were detected in 342 (91.93%) of the samples of which 28.76% were single positive and 63.17% had multiple infections. The most frequent detected viruses were rhinovirus (55.64%), respiratory syncytial virus A/B (33.06%), adenovirus (25.00%), coronavirus NL63, HKU1, OC43, and 229E (21.50%), and metapneumovirus A/B (16.12%). Children in the youngest age group (1-3 months) exhibited the highest frequencies of infection. Related to their frequency of detection, RSV A/B was the most associated pathogen with patient's demographic situation and clinical manifestations (p<0.05). Parainfluenza virus 1-4 and parechovirus were found to increase the risk of death (p<0.05). Adenovirus was statistically associated to the manifestation of gastroenteritis (p = 0.004). Rhinovirus infection increases the duration of oxygen support (p = 0.042). Coronavirus group was statistically associated with the manifestation of bronchiolitis (p = 0.009) and laryngitis (p = 0.017). Streptococcus pneumoniae DNA was detected in 143 (38.44%) of tested samples. However, only 53 samples had a concentration of C-reactive protein from equal to higher than 20 milligrams per liter, and 6 of them were single positive for Streptocuccus pneumoniae. This study confirms the high incidence of respiratory viruses in children hospitalized for acute respiratory tract infections in the Sousse area, Tunisia.