Abstract
Neisseria meningitidis is a human exclusive pathogen that can lead to invasive meningococcal disease or may be carried in the upper respiratory tract without symptoms. The relationship between carriage and disease remains poorly understood but it is widely accepted that decreasing carriage by immunization should lead to a reduction of invasive cases. Latin America has experienced an increased incidence of serogroup W invasive cases of Neisseria meningitidis in the last decade. Specifically in Chile, despite low total incidence of invasive cases, serogroup W has become predominant since 2011 and has been associated with elevated mortality. Expecting to gain insight into the epidemiology of this disease, this study has used molecular typing schemes to compare Neisseria meningitidis isolates causing invasive disease with those isolates collected from adolescent carriers during the same period in Chile. A lower carriage of the serogroup W clonal complex ST-11/ET37 than expected was found; whereas, the same clonal complex accounted for 66% of total invasive meningococcal disease cases in the country that year. A high diversity of PorA variable regions and fHbp peptides was also ascertained in the carrier isolates compared to the invasive ones. According to the results shown here, the elevated number of serogroup W invasive cases in our country cannot be explained by a rise of carriage of pathogenic isolates. Overall, this study supports the idea that some strains, as W:cc11 found in Chile, possess an enhanced virulence to invade the host. Notwithstanding hypervirulence, this strain has not caused an epidemic in Chile. Finally, as genetic transfer occurs often, close surveillance of Neisseria meningitidis strains causing disease, and particularly hypervirulent W:cc11, should be kept as a priority in our country, in order to prepare the best response to face genetic changes that could lead to enhanced fitness of this pathogen.
Highlights
Neisseria meningitidis (NM) is an aerobic Gram-negative diplococcus
invasive meningococcal disease (IMD) rates are extremely high in countries belonging to the so called “meningitis belt” in sub-Saharan Africa, where seasonal epidemics occur at rates of 10–1,000 cases/100,000 population [1]
The high rate of hypervirulent W:cc11 IMD cases in Chile, in a context of a general low incidence of disease, is an interesting phenomenon especially due to the very low carriage rate found for this strain during the same epidemiological year
Summary
Neisseria meningitidis (NM) is an aerobic Gram-negative diplococcus. This human pathogen is a member of the Neisseriaceae family and can cause localized or invasive infections. Confirmed cases of IMD in this region were mostly caused by NM serogroup A throughout years 2004 to 2009 and by serogroup W between 2010 and 2013 [5] with localized epidemics of NM serogroup X [6]. Countries with lower incidences have been rather dominated by a specific serogroup: Serogroup B constituted 74% of IMD cases between the years 2004 and 2014 in several EU/EEA countries [9], the same serogroup dominated at least between 2000–2007 in Sweden [10], and predominated in West Australia between 2000 and 2014 [11]. Due to the elevated mortality rates of this strain, in 2012 the Ministry of Health implemented an immunization program with a tetravalent vaccine for all children aged 9 months to 5 years and maintained thereafter for 1-year old children
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