The Capnocytophaga canimorsus Isolate That Caused Sepsis in an Immunosufficient Man Was Transmitted by the Large Pine Weevil Hylobius abietis

Abstract

The first vector-borne Capnocytophaga canimorsus sepsis case is presented. An immunocompetent male who denied any contact with canines and who worked in a sawmill was bitten on his neck by a large pine weevil (Hylobius abietis L.; Coleoptera: Curculionidae). Bacteriological diagnosis was confirmed by 16S rRNA gene sequence analysis.

CASE REPORT

A 44-year-old maintenance man worked in a sawmill in Southern Savo, Finland. In the early summer, a large pine weevil bit him on the lateral side of his neck. The bite mark was a red patch of 3 to 4 cm in diameter on his skin, with a darker-red, raised center, and was noticed when he was admitted to the hospital 3 days later. He was septic and febrile (38.6°C), though cardiovascularly stabile. Cellulitis was noted, and arthritis of his left shoulder joint was suspected, because pain limited his shoulder movements. Laboratory examinations revealed slight hyperglycemia (8.2 mmol/liter) at the emergency room, but later values were normal. The joint aspirate revealed neither live bacteria nor their DNA. C-reactive protein was at its highest at 165 mg/liter (reference level of <3). His blood count analysis was normal. At the interview, the patient claimed that he had no domestic animals, nor did he get licked or bitten by any canines in his household, workplace, or other proximities. He had no apparent immunodeficiency state but suffered from gastroesophageal reflux disorder. Two years earlier, he had extensive erysipelas (Streptococcus pyogenes) infection of his right lower limb.

On the fourth day after venipuncture, two aerobic blood culture bottles (bioMérieux, Marcy l'Etoile, France) were positive. The bacteria grew on chocolate agar and on sheep blood agar (5% CO₂ atmosphere) as alfa-hemolytic colonies but very slowly on anaerobe basal agar with 10% horse blood (ABA; Oxoid Ltd., Basingstoke, Hampshire, England). Two days later, one anaerobic blood culture bottle became positive too. On Gram staining, fusiform medium to long Gram-negative cells with tapered ends were observed. This strain gave a weak catalase reaction and was negative in oxidase reaction. The isolate was finally identified in a reference laboratory (Huslab, Helsinki, Finland) by sequencing a 528-bp fragment of a 16S rRNA gene as described previously (1). The primers for amplification were (5′→3′) AGAGTTTGATCMTGGCTCAG (positions 8 to 27) and GTATTACCGCGGCTGCTG (positions 536 to 519). The NCBI BLAST analysis yielded sequence homology of only 95% identity with 76 shots. The first 10 were GQ167565.1, KC866279.1, NR_074409.1, JQ259376.1, JN713400.1, AB649272.1, CP002113.1, HQ454087.1, FJ669154.1, and EU124407.1. The sequence was also analyzed with the Isentio RipSeq program (allowing alignment of mixed sequences from the mixed culture, keeping in mind that the weak identity using BLAST was due to some contaminating strains. This new analysis gave 100% identity with Capnocytophaga canimorsus accession numbers AY643075, CP002113 (the same as in the BLAST analysis), NC_015846, and FJ669153. The strain was susceptible to ampicillin, meropenem, and ciprofloxacin.

The patient and his colleagues were aware that large pine weevils (Hylobius abietis L.) were common within the tall timber that they worked with during the spring swarming period, which coincided with the reproductive season of the insect. Thus, they had a high degree of awareness and skills to identify the insect. The antibiotic treatment was started with empirical parenteral cefuroxime and followed with oral cephalexin. When the pathogen was identified from the blood culture, cephalosporins (8 days) were replaced by oral amoxicillin-clavulanate (10 days). The patient recovered uneventfully. His hospitalization lasted 4 days with subsequent outpatient review.

Here, we present a case of sepsis caused by C. canimorsus that to the best of our estimation was vector transmitted. There is no information whether large pine weevils can intermittently carry C. canimorsus in its oral cavity or whether these microbes represent its normal microbiota. However, we suggest its vector-borne transmission on the basis of the following arguments: (i) The patient denied any direct or indirect contact with dogs or cats and denied their bites or licks. (ii) The large pine weevil can occasionally bite humans (H. Viiri, unpublished data) or even dogs. (iii) Our patient and his coworkers can recognize large pine weevils, because since childhood they have been living close to forest areas, where these weevils occurred in large quantities during the swarming period after fresh logging of conifers.

Capnocytophaga canimorsus is a commensal Gram-negative capnophilic bacterium in the oral cavity of canines. The human isolates of this bacterium are mainly from blood or spinal fluid cultures of persons bitten by dogs or cats or being exposed to their scratches or licks (2). Infections caused by C. canimorsus can be potentially life threatening in patients with immune suppression, such as the state after splenectomy, malignancies, cytostatic or radiation therapy, or alcoholism. C. canimorsus resists phagocytosis by macrophages and killing by complement. Without sufficient proinflammatory response, C. canimorsus infection can lead to sepsis or meningitis with a high mortality rate. This bacterium is a zoonotic agent, and, e.g., in the Netherlands it has been considered an emerging zoonosis (3). The microbiological workup may be sometimes tedious because of the microbe's fastidious growth. Phenotype-based methods such as VITEK2 or matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) may not be successful in identification of all strains (4). 16S rRNA gene sequencing analysis is robust and, at present, is the most adequate diagnostic tool (5) for bacterial taxonomy.

The large pine weevil H. abietis (Coleoptera: Curculionidae) is a serious insect pest in recently established coniferous forests (6). For example, in Finland and Sweden, more than 100,000 ha of forest plantations are endangered every year. Pine weevils occur throughout all temperate European and Asian coniferous forests (7). Logging of coniferous trees produces an enormous increase in breeding resources. Females start oviposition in the bark and lateral roots of freshly felled stumps. After oviposition, females and accompanying males start feeding (8). Feeding takes place during the whole vegetation period, including two peak times of feeding damage: one in spring before oviposition and a second one in autumn, when pine weevils prepare for overwintering. Depending on ambient temperature and the quality of the host material, the development of larvae, pupation, and emergence of the pine weevil can take place in the course of 1 year from egg laying. In cold climate conditions, development can last for 5 years, pine weevil individuals are able to live up to 4 years (8), and their reproductive period is very long. Taking advantage of these facts, the pine weevil is able to establish populations with a high number of individuals belonging to overlapping generations. Further, emergence and migration of the pine weevil lead to fast and large-scale fluctuations in individual numbers. Eggs, larvae, and pupae develop underground, which makes it difficult to monitor and to control them.

In conclusion, vector-borne infection by C. canimorsus is possible and should be considered an emerging threat, especially in the areas where a population lives and works in close contact with fresh timber, like many inhabitants of Eastern Finland.