Rat bite fever: some comments on a case report review.

Dear Editor, I like to make some comments on a case report review with the focus on the rare zoonotic infection rat bite fever (RBF) written by Coessens and De Laere [1]. Firstly, I agree with the authors that the literature on RBF is sparse for a zoonosis that has been recognized since ancient times [2]. By only summarizing 20 articles about European case reports, some points of view could have been overlooked. Moreover, a thorough PubMed database search strategy and performing a backward citation search could have yield twice as many interesting papers about European case reports published in English or Dutch in the last 20 years (2001–2020) [3,4]. So, there are several limitations to Coessens et al. review that are related to the breadth and depth of information, half of the cases may be missed (I retrieved other case reports from France, Germany, The Netherlands, also nonmentioned cases from Denmark, Poland, Spain, and Switzerland, n = 40). For instance, only 4/20 were cases among children, although RBF is a growing pediatric issue, as mentioned by Coessens and De Laere themselves. Secondly, rat bites account for approximately 1% of animal bites, with the risk of Streptobacillus moniliformis infection following a bite is about 10% [4]. RBF incidence must be largely underestimated due to frequent misdiagnoses (e.g. viral illness or rheumatologic disease), specialized techniques required to recover the microorganism from cultures, and lack of obligatory reporting of RBF infections [5]. Recently, various publications have suggested that Streptobacillus spp. might be far more common than previously thought [6]. The recent findings of Kache et al. (2020) of all cases reported in the period 2001–2015 in the United States reinforce that rat bite fever is rare, yet suggest it occurs more frequently than previously demonstrated in the review of 65 cases by Elliott in 2007 [6,7]. Thirdly, RBF may indeed be a misnomer, approximately 30% of patients do not report having been bitten or scratched by rodents [6]. Transmission occurs by a bite or scratch of a rodent or a predator of rats; mucocutaneous contact with the saliva, urine, or feces of a rat; as well as by ingestion of food or water contaminated by a rat. The infection may be acquired by handling rats, without any apparent breach of intact skin or with a portal of entry, such as varicella lesions. So, non-traumatic transmission has been reported more frequently, e.g. via mucous membranes (kissing a rat) [8]. The cases without clear rat bite or scratch exposure highlight the need for a thorough history before removing RBF from the differential diagnosis [9]. Ingestion leads to the gastrointestinal form of disease known as ‘Haverhill fever’, characterized by pharyngitis and vomiting. Fourthly, RBF is a diagnostic dilemma due to missing notice of a rodent bite (or contact), non-specific clinical symptoms, fastidious growth of the widely unknown microorganism and broad chemotherapeutic susceptibility, antibiotic prophylaxis (especially beta-lactam antibiotics) after rat bites, a non-notifiable disease, broad extensive spectrum of differential diagnoses but with RBF low on the differential, unsuitable diagnostic tools, isolation, and identification is not straightforward [4,6]. Additionally, only very severe clinical cases will be diagnostically worked up and few laboratories and physicians are experienced with RBF or are even aware of this disease [6]. Finally, the domestication of rodents has led to a broadening of the epidemiology of RBF to include pet rodent owners and pet store employees [10]. With the increase in rodent handling, there has been concomitant increase in rat bites. Importantly, there has been a striking increase in the number of owners of exotic pets and wildlife that may have had close contact with rodents [8]. More and more live rats are being purchased due to the popularity of the Harry Potter movies (‘Ron’s pet rat’) and also to feed snakes (live) rats (vivarium owners) [10]. RBF is an under-recognized, under-diagnosed, and under-reported disease. Therefore, awareness of RBF must be enhanced. RBF should occupy a more prominent place in our diagnostic thinking. Clinicians should obtain a thorough zoonotic exposure history by asking about rodent encounters in the form of pests and pet rats (and mice) and maintain a broad differential diagnosis that includes RBF with any fever or infection of unknown origin [5].