New concepts for the old challenge of African relapsing fever borreliosis

Relapsing fever, caused by spirochaetes belonging to the genus Borrelia , was once the cause of worldwide epidemic disease. This was largely through infection with the louse-borne form of the disease, caused by Borrelia recurrentis (louse-borne relapsing fever (LBRF)). During the last century, we have witnessed the demise of this infection, largely owing to improved standards of living and the introduction of the insecticide DDT, resulting in a reduction in the incidence of the body louse, the vector for relapsing fever. In areas of extreme poverty this disease persists, causing a significant burden of disease. It is now looking probable that this infection is caused by a louse-adapted variant of Borrelia duttonii , transmitted by Ornithodoros moubata 'soft' ticks in East Africa. Like LBRF, infection still causes impact, particularly affecting young children and pregnant women. Over recent years, the true burden of relapsing fever caused by infection with the closely related Borrelia crocidurae , transmitted by Ornithodoros sonrai ticks, has only just begun to emerge. Here, the current state of knowledge concerning relapsing fever in Africa is reviewed.     

Relapsing fever borreliosis in Eurasia—forgotten, but certainly not gone!

Tick-borne relapsing fever (TBRF) has been reported in Eurasia and attributed mainly to Borrelia persica , although other entities have also been described. Ornithodoros tholozani is the most important tick vector, found in India and Kashmir, the southern countries of the former USSR, Iran, Iraq, Syria, Jordan, Turkey, Israel, Egypt, and Cyprus. It inhabits caves, ruins, and burrows of rodents and small mammals. In the northern countries, O. tholozani also lives in houses and cowsheds. In Israel, 30–60% of caves were found to be infested. PCR studies of Borrelia infection of O. tholozani ticks collected in caves showed very variable rates, ranging from less than 2% to 40%. The number of human cases reported varies among countries, from eight cases per year in Israel to 72 cases per year in Iran. The incubation period is 5–9 days. The fever attacks last from several hours to 4 days, and are accompanied by chills, headache, nausea and vomiting, sweating, abdominal pain, arthralgia, and cough; complications are rare. Other described Borrelia species are Borrelia caucasica , Borrelia latyschewii , Borrelia microtii , and Borrelia baltazardi . The classic taxonomy based on the co-speciation concept is very complex and very confusing. For this reason, 16S rRNA and flaB genes were used for taxonomic clarification. Sequencing of Israeli TBRF flaB genes, from human and tick samples, has demonstrated a third cluster corresponding to the Eurasia strains, in addition to both New World and Old World clusters. Thin and thick blood smears remain the most frequently used methods for laboratory diagnosis, with a sensitivity of 80%. PCR-based diagnosis is the most sensitive method, and has the advantage of allowing species identification.     

Understanding tropism and immunopathological mechanisms of relapsing fever spirochaetes

Mice infected with relapsing fever (RF) spirochaetes survive recurrent waves of high-level bacteraemia with little, if any, clinical complications or tissue injury. In the absence of B-cells, peak bacteraemia does not resolve, resulting in multi-organ complications. During peak bacteraemia, large amounts of interleukin-10 (IL-10) are produced in blood and tissues. In mice unable to clear peak bacteraemia, exogenous IL-10 greatly reduced the clinical manifestations, serum levels of CXCL13, cerebral microgliosis, and the pathogen load. In contrast, IL-10 deficiency in mice unable to clear peak bacteraemia resulted in microvascular complications with distinct severities, depending on the serotype: serotype 2 (Bt2), which causes peak bacteraemia of c.  10⁸/mL, resulted in rapid death from subarachnoid and intraparenchymal haemorrhage; in contrast, serotype 1, which causes peak bacteraemia of c.  10⁷/mL, resulted in milder multi-organ haemorrhage and thrombosis. IL-10 deficiency also resulted in multi-organ haemorrhage and thrombosis with infarction in wild-type mice despite lower peak bacteraemia. Two mechanisms for pathogen control have been identified: antibody clearance of peak bacteraemia, and antibody-independent lowering of bacteraemia via phagocytosis in the spleen. IL-10 plays opposite roles in pathogen control, depending on the severity of bacteraemia: during persistent high bacteraemia, IL-10 helps to control it by protecting innate immune cells from apoptosis; in contrast, during transient peak bacteraemia, IL-10 slows down antibody-mediated clearance. A successful outcome from RF depends on a balanced immune response to clear bacteraemia while avoiding microvascular injury, in which production of IL-10, in response to the pathogen load, plays a critical role.     

Prevalence of tick‐borne encephalitis virus in Ixodes ricinus ticks from three islands in north‐western Norway

Tick‐borne encephalitis (TBE) is the most important viral tick‐borne disease in Europe and can cause severe disease in humans. In Norway, human cases have been reported only from the southern coast. The aim of this study was to investigate the prevalence of tick‐borne encephalitis virus (TBEV) in questing Ixodes ricinus ticks from the north‐western part of Norway. A total of 4509 ticks were collected by flagging in May and June 2014. A subpopulation of 2220 nymphs and 162 adult ticks were analysed by real‐time PCR and positive samples were confirmed by pyrosequencing. The estimated prevalence of TBEV was 3.08% among adult ticks from Sekken in Møre og Romsdal County and 0.41% among nymphs from both Hitra and Frøya in Sør‐Trøndelag County. This study indicates that TBEV might be more widespread than the distribution of reported human cases suggests.     

Borrelia hispanica in Ornithodoros erraticus, Portugal

Tick-borne relapsing fever (TBRF) is a spirochetal infection caused by the genus Borrelia. The disease is distributed in the Old and New World with many different species reported. In Europe, TBRF is caused by B. hispanica transmitted to man by Ornithodoros erraticus, a soft tick usually found in old premises to shelter pig herds. In Portugal, the first human case of TBRF was reported in 1942 but since the beginning of the 1960s, the disease has rarely been described and seems to either have disappeared or have been undiagnosed. Therefore, in 2009 a survey was undertaken to evaluate the presence of the tick in this type of premises and to evaluate its role as a reservoir of Borrelia. The work was carried out where the ticks were previously reported in the Alentejo and Algarve regions. Of 63 pigpens surveyed, O. erraticus was collected from 19% (n = 12) of these pigpens using CO(2) traps. To evaluate potential Borrelia hosts, both pigs (n = 25) and small rodents (n = 10) inhabiting these pigpens were surveyed for Borrelia presence, by whole blood PCR and/or tissue culture, respectively. All results for pigs and rodents were negative for the presence of B. hispanica. PCR assays targeting the 16S rRNA gene and intergenic spacer region of Borrelia were used. Sequence analysis of the positive samples confirmed the presence of B. hispanica in 2.2% (n = 5) of ticks from a pigpen in Alentejo. These results confirm natural, but albeit low, persistence of this agent in Portugal.     

Evaluation of the serum levels of soluble IL‐2 receptor and endothelin‐1 in children with Crimean‐Congo hemorrhagic fever

We aimed to assess the association between serum levels of soluble IL‐2 receptor (sIL‐2r) and endothelin‐1 and severe infection in children with Crimean‐Congo hemorrhagic fever (CCHF). Fifty‐two patients under 18 years of age with a laboratory‐ confirmed diagnosis of CCHF and 38 healthy controls were enrolled in the study. Patients were classified into two groups based on disease severity (severe group and non‐severe group). The sIL‐2r and endothelin‐1 levels were observed to be significantly higher in patients with severe CCHF compared with those with non‐severe CCHF and the control group (p < 0.05). In addition, those with non‐severe CCHF were also found to have a significantly higher sIL‐2r level relative to the control group (p < 0.001). Although there was a positive correlation between sIL‐2r and endothelin‐1 levels, serum levels of both sIL‐2r and endothelin‐1 were negatively correlated with the platelets count. In children with CCHF, serum levels of sIL‐2r and endothelin‐1 were increased, and this increase is related to the severity of the disease. In this study, we concluded through prognosis that serum levels of sIL‐2r and endothelin‐1 might be related, and that hemophagocytic lymphohistiocytosis and endothelial injury might contribute to a pathogenesis of the disease.     

Clinical evaluation of highly pathogenic tick‐borne flavivirus infection in the mouse model

The objective of this study was to evaluate the feasibility of using clinical parameters to demonstrate disease progression and differentiate between Omsk hemorrhagic fever virus (OHFV) and Russian spring‐summer encephalitis virus (RSSEV) infection in the mouse model. Adult C57BL/6 and balb/c mice were infected with either OHFV or RSSEV by footpad inoculation and their temperature, body weight, clinical signs complete blood count, and blood chemistries were evaluated for up to 15 days post‐infection (dpi). Clinical evaluation showed that OHFV infection seriously affects balb/c mice, which had shorter average survival times (ASTs) than other groups. On the contrary, RSSEV infection of C57BL/6 mice was more severe than in balb/c mice. During these studies, the development of fever was not observed and the body weight of OHFV infected balb/c and C57BL/6 mice began to decline sharply starting from day 7 and 8, respectively, which correlated with disease onset. Peak increase of globulin and neutrophils was demonstrated after 9 dpi in OHFV infected mice; however, the lymphocyte number was not affected. Viremia was undetectable in these animals with either virus infection, but virus was found in most organs tested. These results indicate marked differences in the clinical signs, pathology, and immune response of mice infected with either OHFV or RSSEV and further validate the use of this mouse model system to evaluate human disease. J. Med. Virol. 81:1261–1269, 2009. © 2009 Wiley‐Liss, Inc.     

Characterization of a novel EAST‐negative enteropathogenic E. coli strain implicated in a food‐borne outbreak of diarrhoea in adults

Enteropathogenic Escherichia coli (EPEC) is usually associated with outbreaks and sporadic cases of severe infantile diarrhoea in the developing world, and less commonly with sporadic cases in developed countries. Very little evidence indicates that EPEC is a food‐borne pathogen for adults. In a previous study, two groups of adult travellers became ill, and eae⁺ E. coli of serogroup O111 was isolated from affected individuals and epidemiologically linked to food consumption. Here the strain responsible was further investigated and characterized as an unusual atypical EPEC. PCR analysis of the designated type isolate showed the presence of the rorf1 and espB genes of the LEE pathogenicity island, which was inserted at the chromosomal selC locus. The isolate was negative for the enteroaggregative E. coli EAST‐1 toxin present in other strains of EPEC associated with food‐borne outbreaks. The strain adhered sparsely to HEp‐2 cell monolayers in a diffuse manner, but fluorescent actin staining demonstrated that it was capable of inducing polymerization of actin at the sites of bacterial attachment. Strain P2583 is the first EAST‐negative EPEC to be confirmed as a cause of outbreaks of infection in adults following the consumption of contaminated food or water.