Scalp eschar and neck lymph adenopathy after a tick bite (SENLAT) in Tuscany, Italy (2015–2022)

The syndrome currently known as Scalp Eschar and Neck Lymph Adenopathy After a Tick Bite (SENLAT) has a history made of several changes in denomination.

Rickettsia slovaca was firstly isolated in Dermacentor spp. tick in 1968 in Slovakia and for several years it was believed not to have any pathogenic role for humans [1]. In 1987, in the Hungarian center for tick-borne diseases, a first case of tick bite on the scalp characterized by appearance of eschar and neck lymphadenopathy was described and many other cases followed. Between 1996 and 1997 this syndrome was termed Tick-borne lymphadenopathy (TIBOLA) by the research group of the Centre National de Référence des Rickettsies, Coxiella et Bartonella, Marseille, France, and it was associated to the isolation of R. slovaca and identification of Dermacentor ticks as vectors [2, 3]. In 2003 R. slovaca was finally isolated in a patient [4]. After being named DEBONEL (Dermacentor-born necrosis, erythema and lymphadenopathy) [5], the last change in terminology was once more introduced by the Marseille group, where the disease was defined as SENLAT, in order to define a clinical entity that is not associated to a precise microbiological diagnosis [6], characterized by a tick bite on the scalp followed by appearance of an eschar on the bite site and neck lymphadenopathy. Other common symptoms are fever, myalgia, neck pain, headache. Appearance of facial edema has been reported, while macular lesions of the extremities or multiple eschars are rare findings [7]. It usually presents as a mild rickettsiosis, but severe forms have been described and prolonged symptoms are reported, mostly if the illness is not appropriately treated [8, 9]. Most common sequelae include alopecia on the eschar site, and chronic asthenia, lasting up to several months [10]. The most common causative agents are R. slovaca and Rickettsia raoultii, but other pathogens have been identified in SENLAT patients, such as Rickettsia massiliae [11, 12], Rickettsia rioja, Rickettsia sibirica mongolitimonae, Bartonella henselae, Coxiella burnetii, Borrelia burgdorferi and Francisella tularensis [13]. No specific clinical pattern has emerged in relation to particular pathogens. Diagnosis of SENLAT is based on clinical-epidemiological features given that no microbiological test can reliably identify all potential pathogens involved in its manifestations. As a consequence, it may be hard to recognize and diagnose this disease. Dermacentor spp. ticks appear to be the most frequently involved vector: Dermacentor marginatus is spread all over Mediterranean areas of Europe and North Africa, while Dermacentor reticulatus is more commonly found in Central and Western Europe and in some areas of Russia [14]. Dermacentor adult ticks are usually active from March to April and from September to October. They climb onto grasses or bushes and wait for their hosts at an height of 0.5–1.5 m [15]. Their biting habits include wild hairy mammals and, among humans, they prefer biting women and children on hairy areas of the body, frequently in the scalp [16]. SENLAT is one of the most common rickettsiosis in Europe, second only to Mediterranean Spotted Fever, and it has been reported in Italy, Spain, France, Hungary, Bulgaria, Portugal [7]. Raoult et al. reported that 19% of tick-borne diseases in Europe are associated with R. slovaca and between 1 and 17% of Dermacentor ticks are reported to be positive for R. slovaca in Europe [2]. According to a systematic literature review, only six microbiologically confirmed cases of SENLAT have been reported in Italy from 1996 to 2021 [16]; in these cases, R. slovaca and R. massiliae were identified with molecular methods as the causative agents [10‐12, 17]. Moreover, R. slovaca, and sporadically R. raoultii, positive Dermacentor ticks were found in Piedmont, Liguria, Sardinia, Tuscany and Abruzzo in wild boars, possibly representing a relevant wild reservoir with a potential role in the eco-epidemiology of rickettsiosis in these regions [18, 19]. We present ten cases of SENLAT seen at a referral center in Central Italy, discussing the clinical characteristics and diagnostic features of our cases.

The Infectious and Tropical diseases department of Careggi University Hospital is located in Florence, Tuscany, central Italy, and includes a regional referral center for tropical and vector-borne diseases. We searched the records of our center for patients seen between January 1st 2015 and May 31st 2022, who presented with symptoms compatible with SENLAT. Data on demographic variables, epidemiological information, clinical data, comorbidities or special circumstances (e.g., pregnancy), laboratory findings, microbiological tests, treatment and outcomes were analyzed.

Our search found ten patients with SENLAT-compatible manifestations. Information about demographic, clinical, microbiological, treatment and outcome features are reported in Table 1.

Clinical and epidemiological features of these cases are coherent with SENLAT. Tick attachment duration ranged between 1 and 10 days, while symptoms appeared between 1 and 14 days after the presumptive day of tick bite; however, reported days of tick bites were only presumptive and a high grade of imprecision should be considered for these results. Indeed, most patients did not note the happening of the tick bite and could only correlate the presumptive timing of the tick bite with the recent outdoor activities performed in rural areas. Presumptive duration of tick attachment did not seem to correlate with symptoms severity in our cases, however the small number of reported cases does not allow to reach any statistical significance.

Scalp eschar (or multiple scalp eschars) and neck lymphadenopathy were observed in the great majority of our patients, coherently with other findings reported in literature [9, 17]. Interestingly, in all cases, scalp eschar appearance was observed between 1 and 7 days after the onset of the first symptoms (that were usually lymphadenopathy and/or fever); further research is needed to define most typical clinical evolution in SENLAT patients and typical timing of appearance of more frequent symptoms. Moreover, scalp eschars appearance could have passed unnoticed for several days, with consequent high probability of imprecision in describing the timing of their onset.

In our case series, a high percentage of patients reported fever, while this symptom has been reported in a lower proportion of cases by other authors [9, 17]; since the study was conducted in a tertiary care center, a selection bias could partly explain this finding.

Microbiological identifications are missing in our cases. This result could be explained by some factors. First of all, tick examination is very helpful in order to get diagnosis, since the identification of a Dermacentor tick, after tick bite on the scalp and associated to typical clinical presentation, is strongly suggestive for SENLAT [2]. Moreover, microbiological study of the tick with molecular tests has an important role in the process of indirect identification of the involved pathogen and has been in some cases the only way to associate SENLAT with a possible pathogen [22]. In our case all patients had removed and thrown the tick before coming to our center, therefore this diagnostic procedure was completely missed.

Molecular diagnosis is the most sensitive way for etiological definition in SENLAT and PCR can be performed either on lesions or lymph nodes biopsies, swabs or blood specimens. However, blood PCR tests do not have high sensitivity due to the localized nature of the disease. It is suggested to perform microbiological investigations as soon as possible after symptoms onset, before any antibiotic treatment and not later than 4 days [22].

In our case, it was impossible to collect early clinical samples. In addition, sensitivity of our microbiological tests was very low due to previously administered antibiotic treatment.

Serologies were negative in all cases; this result is coherent with literature and explained by the fact that serology is not believed to be sensitive in this kind of syndrome, due to its localized nature and evolution [2].

Absence of pathogen isolation is in line with previously reported cases described in literature: as an example, a review by Pinto et al. reported that only 30% of cases are associated with any microbiological direct identification [14]. This evidence strengthens the hypothesis of presence of still unknown mechanisms and/or pathogens causing the syndrome [2]; in fact, SENLAT has been described as a non-pathogen-specific reaction to Dermacentor ticks’ bites or to any microorganism carried by these ticks [9, 21].

Finally, it should be noted that a strong host-parasite association has been demonstrated among wild boars and D. marginatus in northern Mediterranean areas, including Tuscany, where 32.1% of tested ticks resulted positive for R. slovaca and 1.8% for R. raoultii, supporting the possible epidemiological role of these arthropods and relative pathogens in the described cases and, more broadly, in tick borne diseases recorded in this region [18, 23].

In conclusion, our experience brings attention to presence of SENLAT cases in Italy, which are rarely reported and likely underdiagnosed. Better awareness and microbiological and clinical knowledge of SENLAT could help avoiding misrecognition of this syndrome and improve the knowledge about appropriate treatment and management of this disease. Further studies, ideally conducted on both patients and ticks, are needed both on the clinical aspects of the disease and on its epidemiological features.