Isolation and characterization of Borrelia burgdorferi strains from Ixodes ricinus ticks in southern England
Sorouri R, Ramazani A, Karami A, Ranjbar R, Guy EC. Bioimpacts. 2015;5(2):71–8.
Full text available from http://bi.tbzmed.ac.ir/JournalIssues/AllIssues/Volume5Issue2/2201552.aspx
LDA was intrigued to come across this paper which was published in the current issue of the open access, multidisciplinary peer reviewed journal Bioimpacts, since it investigates tick infection rates with Borrelia burgdorferi and local strains of the bacteria in ticks at various rural sites in southern England, which is an under-researched area. Interestingly, the first three authors are from University Medical Sciences departments in Iran and the last is from the Toxoplasma Reference Laboratory (TRL) in Wales. Financial support was received from the University of Southampton and Baqiyatallah University of Medical Sciences in Tehran.
Within the UK, Public Health England is currently studying the epidemiology of ticks, but not the diseases they carry. In Scotland the European Space Agency is helping with similar research to map areas of highest risk for ticks there.
What was studied?
In this study over 1000 ticks were collected from animal carcasses and by blanket dragging at various rural locations in the south of England, including sites in Wiltshire, East Dorset, Hampshire and Richmond Park. It is not clear what species the animals were nor how the animal carcasses were obtained. The tick mid-guts were removed and cultured in BSK medium, which supports the growth of Borrelia. Samples of this were then examined by immunofluorescence (IF), dark-field microscopy and nested PCR.
What did they find?
From the 555 cultured ticks, 2 samples which were positive by IF yielded a positive culture for Borrelia. These cultures were named UK strains SO-1 (isolated from an adult tick, collected from Grovely Wood) and SO-2 (isolated from an adult tick, collected from Savernake Forest). The paper does not state which genospecies these strains belong to.
In addition the team investigated the incidence of B. burgdorferi infection of Ixodes ricinus ticks in the areas studied. The incidence of B. burgdorferi infection in ticks tested in this study varied from 0 -25% at New Forest sites, 53% in Savernake Forest, 60% at Grovely Wood and Great Ridge in Wiltshire, with the highest being Harewood Forest in Hampshire at 67%. In Richmond Park, 13% of ticks tested were infected. We suspect that B. valaisiana may have been included in these infection rates as it has been previously shown to be the most common species.(1)
Many similarities and some differences were seen between the two UK strains and the foreign strains used as laboratory standards (B. afzelii ACA-1 (Sweden), B. burgdorferi B-31 (USA), strains 2B45, 3B56, and 7B49 from Germany). One major difference observed was the presence of a major band at 21-22 kDa in the UK isolates which was not apparent in the standard strains of B burgdorferi. The Virastripe IgG immunoblot currently in use in England which contains antigens from both B31 and B. afzelii (PKo strain) does contain p21 band.
Monoclonal antibody typing showed that UK strain SO-2 was Type 2, in terms of its capacity to spread via the bloodstream. This implies an intermediate tendency to disseminate, with Type 1 being highly likely and Type 3 the least invasive.(2) UK strain SO-1 was not typable but appears to resemble European strains.
This is a small study and so results cannot be extrapolated across the UK, and LDA has some questions on the figures in the text and abstract which remain to be resolved.
Why is this important?
There is very little knowledge of strains of B burgdorferi in the UK. The James Lind Alliance project, funded by LDA, found that one of the top 10 research priorities is to discover “How effective are the current UK tests in detecting infections due to the genospecies and strains of B burgdorferi sl in the UK”. Until we know something about the strains we cannot know how effective the tests may be.
Points of specific interest from this study:
- Previous researchers have found UK strains of B burgdorferi very difficult to culture,(3) and it is notable that out of 555 cultured ticks only 2 produced successful cultures.
- There appear to be differences between UK strains and those used for the manufacture of diagnostic test kits though the significance of this is not yet clear.
- These researchers, unrelated to current research teams working on UK Lyme disease, have re-activated the awareness of uncertainties in this area which used to exist in the early 1990s.
Where now?
It will be interesting to discover which genospecies were identified and which are represented in the 2 successful cultures. LDA is in correspondence with the authors to discover more detail about this fascinating study. One of the benefits of freely available research papers is the dialogue that is enabled.
References
1. Bettridge J, Renard M, Zhao F, et al. Distribution of Borrelia burgdorferi sensu lato in Ixodes ricinus Populations Across Central Britain. Vector Borne Zoonotic Dis 2013; 13.
2. Wormser GP, Brisson D, Liveris D, et al. Borrelia burgdorferi genotype predicts the capacity for hematogenous dissemination during early Lyme disease. J Infect Dis 2008; 198: 1358–1364.
3. Livesley MA, Carey D, Gern L, et al. Problems of isolating Borrelia burgdorferi from ticks collected in United Kingdom foci of Lyme disease. Med Vet Entomol 1994; 8: 172–178.
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