The serological and genetic diversity of the Leptospira interrogans Icterohaemorrhagiae serogroup circulating in the UK

Abstract

Introduction: Strains of Leptospira interrogans belonging to two very closely related serovars, Icterohaemorrhagiae and Copenhageni, have been associated with disease in mammalian species and are the most frequently reported agents of human leptospirosis. They are considered the most pathogenic serovars and represent more than half of the leptospires encountered in severe human infections.

Material and methods: Nineteen such isolates from the United Kingdom - human, domestic and wildlife species - were typed using three monoclonal antibodies (F12 C3, F70 C14 and F70 C24) in an attempt to elucidate their epidemiology. They were further examined by restriction endonuclease analysis (REA), multiple-locus variable-number tandem repeat analysis (MLVA) and lic12008 gene sequence analysis.

Results: Monoclonal antibody F12 C3, which is highly specific for Icterohaemorrhagiae and Copenhageni, confirmed that all the strains belonged to these two serovars. Sixteen strains were identified as Copenhageni and three as Icterohaemorrhagiae serovar. Only one restriction pattern type was identified, thus confirming that REA is not able to discriminate between the Icterohaemorrhagiae and Copenhageni serovars. Variable-number tandem-repeat analysis found three loci with differences in the repeat number, indicating genetic diversity between British isolates. Sequences of the lic12008 gene showed that all isolates identified as the Icterohaemorrhagiae serotype have a single base insertion, in contrast to the same sequences of the Copenhageni serotype.

Conclusion: Copenhageni is the predominant serovar in the Icterohaemorrhagiae serogroup isolated in British Isles. There is a genetic diversity of MLVA patterns of the isolates but no genetic tool used in the study was able to determine serovars.

Keywords: Copenhageni; Icterohaemorrhagiae; Leptospira; animal pathogens; leptospirosis.

Fig. 1.

Restriction endonuclease analysis patterns of chromosomal DNA from Leptospira strains digested with EcoRI. Lanes: 1 – Icterohaemorrhagiae (RGA strain); 2 – Copenhageni (M20 strain); 3 – Monymusk (LT 75-68 strain); 4 – Budapest (PV-1 strain); 5 – Mankarso (Mankarso strain); 6 – Naam (Naam strain); 7 – Birkini (Birkin strain); 8 – Bogvere (LT 60-69 strain); 9 – Dakota (Grand River strain); 10 – Gem (Simon strain); 11 – Lai (Lai strain); 12 – Mwogolo (Mwogolo strain); 13 – Ndambari (Ndambari strain); 14 – Ndahambukuje (Ndahambukuje strain); 15 – Smithi (Smith strain); 16 – Tonkini (LT 96-68 strain)

Fig. 2.

Unweighted pair-group method with arithmetic mean (UPGMA) tree based on the 12 variable-number tandem-repeat (VNTR) loci (V4, V7, V9, V10, V11, V19, V27, V29, V30, V31, V36 and V50). As only a partial repeat was present in V23 for all studied isolates, this locus was omitted in the UPGMA cluster analysis. Different VNTR profiles of 19 isolates revealed 5 distinct genotypes (A to E)