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Clonal analysis of the serogroup B meningococci causing New Zealand's epidemic
1Communicable Disease Group, Institute of Environmental Science and Research, Porirua, New Zealand.
Abstract:
An epidemic of meningococcal disease caused by serogroup B meningococci expressing the P1.7-2,4 PorA protein began in New Zealand in 1991. The PorA type has remained stable. Different porB have been found in association with the P1.7-2,4 PorA, although type 4 has been most common. The clonal origins of B:P1.7-2,4 meningococci isolated from cases during 1990 to the end of 2003 were analysed. In 1990, the year immediately preceding the recognized increase in disease rates, all three subclones (ST-41, ST-42, and ST-154) of the ST-41/44 clonal complex occurred among the five isolates of B:P1.7-2,4. The two sequence types, ST-42 and ST-154, continued to cause most disease throughout New Zealand. Isolates belonging to subclone ST-41 were mostly identified early in the epidemic and in the South Island. 16S rRNA typing indicated that isolates belonging to the subclones ST-41 and ST-154 share a common ancestor, with those typing as ST-42 more distantly related with some genetically ambiguous. It is possible that ST-41 and ST-154 may have evolved one from the other but evolution to ST-42 is more difficult to explain. It is possible that one or more of the ST types could have been introduced into New Zealand prior to the first detection of clinical cases in 1990. Genetic diversity may have occurred during carriage in the community.
Insights
The 1991 New Zealand meningococcal disease epidemic, caused by B:P1.7-2,4 strains, involved multiple subclones. ST-42 and ST-154 were most prevalent, with ST-41 appearing early, suggesting complex origins and evolution.
Area of Science:
- Microbiology
- Epidemiology
- Genetics
Background:
- An epidemic of serogroup B meningococcal disease emerged in New Zealand in 1991, characterized by the P1.7-2,4 PorA protein.
- The P1.7-2,4 PorA type remained consistent throughout the epidemic, though variations in the porB gene were observed.
Purpose of the Study:
- To analyze the clonal origins of B:P1.7-2,4 meningococci isolated in New Zealand between 1990 and 2003.
- To understand the evolutionary relationships between different sequence types (STs) of these meningococcal strains.
Main Methods:
- Analysis of meningococcal isolates from cases between 1990 and 2003.
- Utilized sequence typing (ST) to identify clonal complexes and subclones.
- Employed 16S rRNA typing to infer phylogenetic relationships.
Main Results:
- In 1990, all three subclones (ST-41, ST-42, ST-154) of the ST-41/44 clonal complex were present.
- ST-42 and ST-154 were the predominant types causing disease throughout the epidemic.
- ST-41 was mainly identified early in the epidemic and in the South Island.
- 16S rRNA typing suggested ST-41 and ST-154 share a common ancestor, while ST-42 is more distantly related.
Conclusions:
- The B:P1.7-2,4 meningococcal epidemic in New Zealand likely involved multiple ancestral strains or significant genetic diversification.
- The distinct evolutionary pathways of ST-41/154 and ST-42 warrant further investigation.
- Introduction of strains prior to 1990 or extensive evolution during community carriage are potential explanations for the observed genetic diversity.
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