Rickettsiosis: A Case Series on Different Clinical Presentation in Children

Mediterranean spotted fever (MSF) is an acute febrile, zoonotic disease caused by Rickettsia conorii. This is transmitted to humans by the brown dogtick Rhipicephalus sanguineus . Although therapy is easy and unexpensive, the different clinical presentation, the lack tick bite in the history or the frequent absence of skin manifestations, often make diagnosis difficult. We here reported four clinical cases of MSF, occurred in a region of central Italy (Abruzzo) with different clinical characteristics, but common epidemiological and anamnestic characteristics.


Introduction
Mediterranean spotted fever (MSF) is a tick-borne acute febrile disease caused by Rickettsia conorii. This pathogen is transmitted to humans by the brown dog tick Rhipicephalus sanguineus, which is both the vector and reservoir of infection and it is endemic in Mediterranean countries and North Africa [1]. Besides, recently others rickettsiosis pathogens have been associated with human diseases (R. slovaca, R. aeschlimanni, R. massilliae, R. monacensis, R. conorii Israelensis) in Europe, and they have been identified in various arthropod hosts, which can parasitize some vertebrates, including the dog [2,3].
Spotted fever group rickettsiosis are re-emerging agents of tickborne diseases in European countries of Mediterranean area. In Italy, especially in Southern (Sardinia, Sicily, Calabria) and Central regions, about 1000 cases/year are reported, with an annual hospitalization rate of 1,36/100.000 persons year. About 20% of cases are reported in pediatric age with a seasonal pattern from April to September [2]. MSF is mostly characterized by flu-like symptoms, maculopapular rash and a black eschar at the site of the tick bite ('tache noir'). Typical symptoms are rarely present at the same time, especially in children, representing a diagnostic challenge.
Early antibiotic treatment, moreover, shortens the symptomatic period of MSF infection and it prevents the occurrence of severe complications [4]. Currently, given the better tolerance and the equal clinical response compared to chloramphenicol and tetracyclines, the macrolides represent the first line treatment, especially in pediatric age [5]. Four clinical cases of MSF are here presented.
They occurred in a region of central Italy (Abruzzo), with different clinical presentation, but common epidemiological and anamnestic characteristics.

Case 1
A 10-year-old Caucasian boy presented an intermittent bi-quotidian fever up to 39.7°C, associated to asthenia and sore throat.
Cough, skin rashes, arthralgia or other symptoms were not referred. Because of the Coronavirus 19 pandemic, in the previous 60 days the family was in domiciliary quarantine in a small town in Abruzzo, living in a rural area near a farm guesting several animals. Antibiotic therapy with azithromycin for two days and after amoxicillin/clavulanic acid for six days was administered with no defervescence. Therefore, the child was conducted to the Emergency Room after 15 fever days. Blood tests revealed increased CRP (110,4 mg/L, nv<5 mg/L), erythrocyte sedimentation rate (ESR: 49 mm/h, nv<20 mm/h) and D-dimer (2,45 mg/L), and a neutropenia (880/uL).
Chest X-ray was normal. An intravenous empiric broad-spectrum antibiotic treatment with ceftriaxone was started. Blood, urine and stool culture were negative. An electrocardiogram and echocardiogram ruled out an endocarditis and a valvular involvement. In addition, abdomen ultrasounds did not find hepatomeg-

Discussion
Rickettsioses are worldwide zoonoses, nowadays re-emerging and changing in distribution in several regions of the world [4].
Rickettsia are a gram-negative, non-spore-forming and obligate intracellular parasites which can use both vertebrate and invertebrate as hosts and as primary reservoirs and vectors [6]. Therefore, a contact with dogs is not necessary and in a large Italian case series this risk factor was reported only by 20.7% of patients [4]. Similarly, only one of our patients reported a prolonged contact with a dog in his history. Recently Pasucci et al. [3] analyzed 603 ticks in Central Italy (Abruzzo and Molise) finding a high rate of Rickettsia infection (50,2%) and 8 different species of Rickettsia, including Rickettsia conorii sp. conorii, which is the most frequent responsible for MSF.3 Generally, after an incubation period between 5 and 10 days after the bite of the infected tick, MSF has a sudden onset, with flu-like symptoms (moderate or high fever accompanied by chills, asthenia, headache, general disorders). The maculo-papular exanthema appears on the 3rd-5th day of illness, first in the wrists and ankles, then spreads to the palms and soles, until it affects the trunk and rarely the face [7]. This is the symptom of a vasculitis related to the infection [8] In pediatric cases, instead, fever and rash are the most common symptoms (about 90% of cases).
Three out of four cases here presented, conversely, were without rash. Non-exanthematic forms can partially explain the discrepancy between the high prevalence of seropositivity and the prevalence of the infection reported in some studies [7] Only for one of our cases it was possible to find the typical eschar and this factor significantly improve the diagnosis. Moreover, the typical eschar is found in 40-60% of pediatric patients [4,8,9] and the most common localizations are the scalp, the neck, and the truncus [7]. The infectious tick bite is painless and often goes unnoticed. A history of tick bite is an important data of the history of the patient, but it is often absent, making diagnosis more difficult.7 Most of our patients were unaware of tick bites, in line with the data in the literature. The non-specific presentation of Rickettsia infection and the absence of typical signs often make differential diagnosis difficult, especially because the history of the tick bite is missing. Symptoms occur mildly in 80% of cases. In presence of peculiar conditions (diabetes, glucose 6 phosphate dehydrogenase deficiency, cirrhosis…) the clinical course can be severe and also fatal (malignant MSF, 1-7 % of cases), because of complications like acute renal failure, thrombocytopenia, myocarditis, pneumonitis, gastric hemorrhage, shock, and even multiple organ failure [10,11]. Involvement of the central nervous system, which has been most frequently reported in adulthood, is extremely rare in children [11,12]. Headache is complained more by adults compared to children, contributing to a milder clinical presentation compared to adults [4,13]. One of our patients, however, developed severe neurological symptoms.
In spite of this clinical presentation variability, some epidemiological-anamnestic features are almost the same and they can guide the clinical suspicion: males are more affected than females; the infection occurs mainly during spring and summer, and mostly in people who live in rural or wooded areas, because of a higher exposure to ticks [2,4,14,15] About laboratory characteristics, acute phase reactants are mildly increased; 4 all our patients experienced increased inflammatory indices. Leucopenia with an alteration of neutrophils is observed in 25-50% of patient;4 in fact, two of our patients presented relative neutropenia. Thrombocytopenia and anemia might also be present4 and one patient presented normochromic normocytic anemia and another one developed thrombocytopenia Hypertransaminasaemia and alteration of coagulation tests are other non-specific common findings.4 Microscopic hematuria with or without mild proteinuria or albuminuria is also observed because of a glomerular involvement [4,8].
The indirect immunofluorescent antibody (IFA) test is the current serological gold standard and reference test [1]. All these clinical, epidemiological and laboratory aspects are summarized in the Raoult [16] score, used to assess the possibility of Rickettsia infection [16]. In all of our patients indeed, despite the atypical presentation, the score was > 25 (table 1). The American Academy of Pediatrics did not recommend tetracyclines for infections in children younger than eight years of age. Macrolides seems to have similar efficacy of doxycycline and chloramphenicol and a significantly better tolerability, especially in children [5,17] Given the milder clinical presentation and the benign evolution of MSF, macrolides (effective against Rickettsia conorii) can be safety used in children [4]. All the patients were successfully treated with oral macrolides, in line with the recent literature data. In conclusion, in presence of acute febrile illness in children, especially in the spring-summer period, it is mandatory to exclude the Rickettsia infection. Luckily, the clinical evolution in children is benign, but sometimes it can be severe. Early treatment can improve the outcome of the child, also shortening the time of defervescence. Contact with dog's ticks 2

Clinical Criteria
Fever higher than 39°C 5 5 5 5 5 Eschar "Tache noire" 5 5 Maculopapular or purpuric eruption 5 Two out of these three clinical criteria 3 3 All the three clinical criteria together 5

Isolation of Rickettsia conorii from blood 25
Detection of R. conorii in skin biopsy using IFA 25

Serological Criteria (Immunofluorescence)
Sole serum with total lg le 1: