First evidence of tick-borne encephalitis (TBE) outside of Hokkaido Island in Japan

Figures & data

Figure 1. Location of participating hospitals, including those with tick-borne encephalitis virus infected case, by prefecture in Japan. Participating hospitals with a tick-borne encephalitis virus infected case are shown with a red circle.

Figure 2. Case definitions for tick-borne encephalitis virus infection, tick-borne encephalitis case, and previous tick-borne encephalitis case, Japan, 2010–2021. CSF = cerebrospinal fluid; ELISA = enzyme-linked immunosorbent assay; IgG = immunoglobulin G; IgM = immunoglobulin M; JEV = Japanese encephalitis virus; NT = neutralization test; TBE = tick-borne encephalitis; TBEV = tick-borne encephalitis virus.

Table 1. Tick-borne encephalitis virus infections among hospitalized patients with encephalitis or meningitis of unknown etiology with residual serum and residual cerebrospinal fluid specimen tested, by participating hospital, Japan, 2010–2021.

Hospital	No. hospitalized patients with encephalitis or meningitis of unknown etiology	No. (%) patients with residual sera available	No. (%) patients with residual CSF available	No. TBEV infections
National Hospital Organization Asahikawa Medical Center	34	0 (0)	34 (100)	0
Hokkaido University Hospital	60	53 (88.3)	22 (36.7)	0
Aomori Prefectural Central Hospital	62	53 (85.5)	58 (93.6)	0
Southern Tohoku General Hospital	5	4 (80.0)	2 (40.0)	0
Jichi Medical University Hospital	45	38 (84.4)	40 (88.9)	0
Nihon University Itabashi Hospital	39	4 (10.3)	35 (89.7)	1^a
National Center of Neurology and Psychiatry	3	3 (100)	3 (100)	0
National Hospital Organization Shinshu Ueda Medical Center	25	3 (12.0)	25 (100)	0
University of Fukui Hospital	13	13 (100)	0 (0)	0
Tenri Hospital	10	7 (70.0)	7 (70.0)	0
Nara Medical University Hospital	30	13 (43.3)	24 (80.0)	0
Okayama University Hospital	53	47 (88.7)	52 (98.1)	1^b
Kurashiki Central Hospital	46	32 (69.6)	39 (84.8)	0
National Hospital Organization Beppu Medical Center	60	40 (66.7)	54 (90.0)	0
Oita Prefectural Hospital	35	21 (60.0)	35 (100)	1^a
TOTAL	520	331 (63.7)	430 (82.7)	3

^a TBE case.

^b Previous TBEV infection.

CSF = cerebrospinal fluid; TBE = tick-borne encephalitis; TBEV = tick-borne encephalitis virus.

Table 2. Enzyme-linked immunosorbent assay and neutralization test results for tick-borne encephalitis virus infected hospitalized patients with encephalitis or meningitis of unknown etiology at 15 participating hospitals in Japan, 2010–2021.

Age yrs. (sex)	ELISA (test result^a)				NT
	Serum		CSF
	IgG	IgM	IgG	IgM	TBEV	JEV	Interpretation
61 (F)	2.90 (–)	0.98 (+/-)	1.09 (–)	0.07 (–)	40	<10	TBE case
24 (M)	3.20 (–)	1.46 (++)	NA	NA	160	<10	TBE case
45 (F)	94.73 (++)	0.45 (–)	0.16 (–)	0.07 (–)	160	<10	Previous TBEV infection

^a (–): negative; (+/-): borderline; (++): positive.

CSF = cerebrospinal fluid; ELISA = enzyme-linked immunosorbent assay; IgG = immunoglobulin G; IgM = immunoglobulin M; JEV = Japanese encephalitis virus; NA = not available; NT = neutralization test; TBE = tick-borne encephalitis; TBEV = tick-borne encephalitis virus.

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.