No evidence for sylvatic cycles of chikungunya, dengue and Zika viruses in African green monkeys (Chlorocebus aethiops sabaeus) on St. Kitts, West Indies.

BACKGROUND: Dengue, chikungunya and Zika viruses (DENV, CHIKV and ZIKV) are transmitted in sylvatic transmission cycles between non-human primates and forest (sylvan) mosquitoes in Africa and Asia. It remains unclear if sylvatic cycles exist or could establish themselves elsewhere and contribute to the epidemiology of these diseases. The Caribbean island of St. Kitts has a large African green monkey (AGM) (Chlorocebus aethiops sabaeus) population and is therefore ideally suited to investigate sylvatic cycles. METHODS: We tested 858 AGM sera by ELISA and PRNT for virus-specific antibodies and collected and identified 9704 potential arbovirus vector mosquitoes. Mosquitoes were homogenized in 513 pools for testing by viral isolation in cell culture and by multiplex RT-qPCR after RNA extraction to detect the presence of DENV, CHIKV and ZIKVs. DNA was extracted from 122 visibly blood-fed individual mosquitoes and a polymorphic region of the hydroxymethylbilane synthase gene (HMBS) was amplified by PCR to determine if mosquitoes had fed on AGMs or humans. RESULTS: All of the AGMs were negative for DENV, CHIKV or ZIKV antibodies. However, one AGM did have evidence of an undifferentiated Flavivirus infection. Similarly, DENV, CHIKV and ZIKV were not detected in any of the mosquito pools by PCR or culture. AGMs were not the source of any of the mosquito blood meals. CONCLUSION: Sylvatic cycles involving AGMs and DENV, CHIKV and ZIKV do not currently exist on St. Kitts.

High specificity and sensitivity of Zika EDIII-based ELISA diagnosis highlighted by a large human reference panel.

BACKGROUND: Zika virus (ZIKV) and Dengue virus (DENV) are often co-endemic. The high protein-sequence homology of flaviviruses renders IgG induced by and directed against them highly cross-reactive against their antigen(s), as observed on a large set of sera, leading to poorly reliable sero-diagnosis. METHODS: We selected Domain III of the ZIKV Envelope (ZEDIII) sequence, which is virus specific. This recombinant domain was expressed and purified for the specific detection of ZEDIII-induced IgG by ELISA from ZIKV-RT-PCR-positive, ZIKV-IgM-positive, flavivirus-positive but ZIKV-negative, or flavivirus-negative sera. We also assessed the reactivity of ZEDIII-specific human antibodies against EDIII of DENV serotype 4 (D4EDIII) as a specific control. Sera from ZEDIII-immunized mice were also tested. RESULTS: Cross-reactivity of IgG from 5,600 sera against total inactivated DENV or ZIKV was high (71.0% [69.1; 72.2]), whereas the specificity and sensitivity calculated using a representative cohort (242 sera) reached 90% [84.0; 95.8] and 92% [84.5; 99.5], respectively, using a ZEDIII-based ELISA. Moreover, purified human IgG against D2EDIII or D4EDIII did not bind to ZEDIII and we observed no D4EDIII reactivity with ZIKV-induced mouse polyclonal IgGs. CONCLUSIONS: We developed a ZEDIII-based ELISA that can discriminate between past or current DENV and ZIKV infections, allowing the detection of a serological scar from other flaviviruses. This could be used to confirm exposure of pregnant women or to follow the spread of an endemic disease.

Evaluation of commercially available serologic diagnostic tests for chikungunya virus.

Chikungunya virus (CHIKV) is present or emerging in dengue virus-endemic areas. Infections caused by these viruses share some common signs/symptoms, but prognosis, patient care, and persistent symptoms differ. Thus, accurate diagnostic methods are essential for differentiating the infections. We evaluated 4 CHIKV serologic diagnostic tests, 2 of which showed poor sensitivity and specificity.

Use of a new single multiplex PCR-based assay for direct simultaneous characterization of six Neisseria meningitidis serogroups.

We developed a new Neisseria meningitidis multiplex PCR to determine six serogroups, including X-specific primers, and to allow direct W135/Y discrimination. This assay offers a simple and low-cost method for serogrouping N. meningitidis from cerebrospinal fluid that could be useful in Africa.

Populations of pharyngeal meningococci in Niger.

This study investigated the carriage of Neisseria meningitidis group W135 (NmW135) belonging to sequence type (ST)-2881, ST-11 and NmA ST-7, as these three lineages have been responsible for sporadic cases in 2003 in Niamey (Niger). ST-7 and ST-11 were also the two genotypes involved in recent outbreaks in the African meningitis belt. Among the 97 Nm isolates obtained from 287 schoolchildren swabbed three times, 1 was identified as NmA, 34 as NmW135, 8 as NmY and 54 were non-groupable (NG). Among the 86 isolates genotyped, 59.3% belonged to ST-192, 24.4% to ST-2881, 5.8% to ST-2880, 4.6% to ST-175, 3.5% to ST-4899, 1.2% to ST-11 and 1.2% to ST-7. Most of the isolates recovered were weakly pathogenic Nm NG ST-192 and NmW135 ST-2881. These results, although preliminary, are important to consider before introduction of a NmA conjugate meningococcal vaccine in Africa.

Meningococcal meningitis: unprecedented incidence of serogroup X-related cases in 2006 in Niger.

BACKGROUND: In Niger, epidemic meningococcal meningitis is primarily caused by Neisseria meningitidis (Nm) serogroup A. However, since 2002, Nm serogroup W135 has been considered to be a major threat that has not yet been realized, and an unprecedented incidence of Nm serogroup X (NmX) meningitis was observed in 2006. METHODS: Meningitis surveillance in Niger is performed on the basis of reporting of clinically suspected cases. Cerebrospinal fluid specimens are sent to the reference laboratory in Niamey, Niger. Culture, latex agglutination, and polymerase chain reaction are used whenever appropriate. Since 2004, after the addition of a polymerase chain reaction-based nonculture assay that was developed to genogroup isolates of NmX, polymerase chain reaction testing allows for the identification of Nm serogroup A, Nm serogroup B, Nm serogroup C, NmX, Nm serogroup Y, and Nm serogroup W135. RESULTS: From January to June 2006, a total of 4185 cases of meningitis were reported, and 2905 cerebrospinal fluid specimens were laboratory tested. NmX meningitis represented 51% of 1139 confirmed cases of meningococcal meningitis, but in southwestern Niger, it represented 90%. In the agglomeration of Niamey, the reported cumulative incidence of meningitis was 73 cases per 100,000 population and the cumulative incidence of confirmed NmX meningitis was 27.5 cases per 100,000 population (74.6 cases per 100,000 population in children aged 5-9 years). NmX isolates had the same phenotype (X : NT : P1.5), and all belonged to the same sequence type (ST-181) as the NmX isolates that were circulating in Niamey in the 1990s. Nm serogroup W135 represented only 2.1% of identified meningococci. CONCLUSIONS: This is, to our knowledge, the first report of such a high incidence of NmX meningitis, although an unusually high incidence of NmX meningitis was also observed in the 1990s in Niamey. The increasing incidence of NmX meningitis is worrisome, because no vaccine has been developed against this serogroup. Countries in the African meningitis belt must prepare to face this potential new challenge.

Carriage of Neisseria meningitidis serogroup W135 ST-2881.

Serogroup W135 ST-2881 meningococci caused a cluster of meningitis cases in Niger in 2003. Of 80 healthy persons in the patients' villages, 28 (35%) carried meningococci; 20 of 21 W135 carrier strains were ST-2881. Ten months later, 5 former carriers were still carriers of W135 ST-2881 strains. The serum bactericidal antibody activity changed according to carrier status.