Relapsing Fever Borreliae: A Global Review

Relapsing fever borreliae were notorious and feared infectious agents that earned their place in history through their devastating impact as causes of both epidemic and endemic infection. More recently they are considered more as an oddity and their burden of infection is largely overshadowed by other infections such as malaria, which presents in a similar clinical way. Despite this, they remain the most common bacterial infection in some developing countries. Transmitted by soft ticks or lice, these fascinating spirochaetes have evolved a myriad of mechanisms to survive within their diverse environments.

Emerging horizons for tick-borne pathogens: from the ‘one pathogen–one disease’ vision to the pathobiome paradigm

Ticks as vectors of several notorious zoonotic pathogens, represent an important and increasing threat for human, animal health in Europe. Recent application of new technology revealed the complexity of the tick microbiome that might impact upon its vectorial capacity. Appreciation of these complex systems is expanding our vision of tick-borne pathogens leading us to evolve a more integrated view that embraces the “pathobiome” representing the pathogenic agent integrated within its abiotic and biotic environments. In this review, we will explore how this new vision will revolutionize our understanding of tick-borne diseases. We will discuss the implications in terms of research approach for the future in order to efficiently prevent and control the threat posed by ticks.

A Case of Canine Borreliosis in Iran Caused by Borrelia persica

Tick-borne relapsing fever is an endemic disease in Iran, with most cases attributed to infection by B. persica, which is transmitted by Ornithodoros tholozani soft ticks. Here, we report spirochetemia in blood of a puppy residing in Tehran, Iran. The causative species was identified by use of highly discriminative IGS sequencing; the 489 bp IGS sequence obtained in our study showed 99% identity (100% coverage) when compared with Borrelia persica sequences derived from clinical cases or from Ornithodoros tholozani ticks. Our IGS sequence also showed 99% similarity over 414 bp (85% coverage) with a strain from a domestic dog, and 96% over 328 bp (69% coverage) with a strain from a domestic cat. Pet-keeping in cosmopolitan cities like Tehran has become increasingly popular in recent years. Animals are often transported into the city in cages or cardboard boxes that might also harbour minute tick larvae and/or early stages of the nymphs bringing them into the urban environment. This may pose a threat to household members who buy and keep these puppies and as a result may come into close contact with infected ticks.

Emerging borreliae – Expanding beyond Lyme borreliosis

Lyme borreliosis (or Lyme disease) has become a virtual household term to the exclusion of other forgotten, emerging or re-emerging borreliae. We review current knowledge regarding these other borreliae, exploring their ecology, epidemiology and pathological potential, for example, for the newly described B. mayonii. These bacteria range from tick-borne, relapsing fever-inducing strains detected in some soft ticks, such as B. mvumii, to those from bat ticks resembling B. turicatae. Some of these emerging pathogens remain unnamed, such as the borrelial strains found in South African penguins and some African cattle ticks. Others, such as B. microti and unnamed Iranian strains, have not been recognised through a lack of discriminatory diagnostic methods. Technical improvements in phylogenetic methods have allowed the differentiation of B. merionesi from other borrelial species that co-circulate in the same region. Furthermore, we discuss members that challenge the existing dogma that Lyme disease-inducing strains are transmitted by hard ticks, whilst the relapsing fever-inducing spirochaetes are transmitted by soft ticks. Controversially, the genus has now been split with Lyme disease-associated members being transferred to Borreliella, whilst the relapsing fever species retain the Borrelia genus name. It took some 60 years for the correlation with clinical presentations now known as Lyme borreliosis to be attributed to their spirochaetal cause. Many of the borreliae discussed here are currently considered exotic curiosities, whilst others, such as B. miyamotoi, are emerging as significant causes of morbidity. To elucidate their role as potential pathogenic agents, we first need to recognise their presence through suitable diagnostic approaches.