Page 253 - TBE_Book_V2_2019

Chapter 12b

TBE in Bulgaria

Iva Christova

History and Current Situation

First cases of probable tick-borne encephalitis Beginning in 2009, the National Reference
(TBE) were reported in 1961 by Andonov et al. Laboratory of Vector-Borne Pathogens
1
in eastern regions of Bulgaria. Possible TBE introduced reliable laboratory diagnosis
cases with the typical biphasic course, methods for TBE, based on polymerase chain
originating from consumption of raw goat reaction (PCR) and enzyme-linked immuno-
milk, were described back in 1953 by sorbent assay (ELISA), and identified the first 3
2
Vaptzarov et al. in southern Bulgaria. confirmed TBE cases in Bulgaria: 2 cases in
7
Investigations in the 1960s were able to 2009 and 1 case in 2012. Two more TBE cases
isolate 3 tick-borne encephalitis virus (TBEV) were identified in 2015 and one case was
strains from Haemaphysalis punctata and 1 reported in 2017.
from Dermatocentor marginatus ticks, from
3 A recent nationwide survey found an overall
goats and sheep in the district of Plovdiv. The
antigenic properties of these 4 virus strains seroprevalence of 0.6% (Figure 4). However,
were identical to the highly virulent strain district analysis showed TBEV seroprevalence
“Hypr” of the European subtype of TBEV to be up to 4.0%-4.8%, indicating that the
3
(TBEV-EU). TBEV infection seems to be more widespread
8
in the country than previously described.
Laboratory diagnosis of TBE, based on Clearly, although TBE cases are reported only
serology using complement fixation assay, was sporadically due to lack of insufficient testing
introduced in Bulgaria in the 1970s. Since then and/or reporting TBEV circulates in Bulgaria,
single case reports of presumed TBE have causing human cases associated (at an
been reported, but these lack reliable unknown level) either with tick bites or
4-5
microbiological confirmation. However, consumption of unpasteurized milk.
investigations of ticks between 1974 and 2002
resulted in the isolation of 8 TBEV strains
6
among 6,849 ticks investigated.

Overview of TBE in Bulgaria

Table 1: Virus, vector, transmission of TBE in Bulgaria

3
Viral subtypes, distribution European subtype of TBEV (TBEV-EU)
Reservoir animals Not known
Dermatocentor marginatus,
Infected tick species (%)
Haemaphysalis punctata
Dairy product transmission Yes

248