Current Status of Vector-Borne Diseases in Croatia: Challenges and Future Prospects

Abstract

Different vector-borne pathogens are present or have (re-)emerged in Croatia. Flaviviruses tick-borne encephalitis (TBEV), West Nile (WNV), and Usutu (USUV) are widely distributed in continental regions, while Toscana virus (TOSV) and sandfly fever viruses are detected at the Croatian littoral. Recently, sporadic clinical cases of Tahyna orthobunyavirus (TAHV) and Bhanja bandavirus infection and seropositive individuals have been reported in continental Croatia. Acute infections and serologic evidence of WNV, TBEV, USUV, and TAHV were also confirmed in sentinel animals and vectors. Autochthonous dengue was reported in 2010 at the Croatian littoral. Lyme borreliosis is the most widely distributed vector-borne bacterial infection. The incidence is very high in northwestern and eastern regions, which correlates with numerous records of Ixodes ricinus ticks. Acute human Anaplasma phagocytophilum infections are reported sporadically, but there are many records of serologic evidence of anaplasmosis in animals. Mediterranean spotted fever (Rickettsia conorii) and murine typhus (Rickettsia typhi) are the main rickettsial infections in Croatia. Human leishmaniasis is notified sporadically, while serologic evidence of leishmaniasis was found in 11.4% of the Croatian population. After the official eradication of malaria in 1964, only imported cases were reported in Croatia. Since vector-borne diseases show a growing trend, continuous monitoring of vectors is required to protect the population from these infections.

Keywords: Croatia; arboviruses; epidemiology; invasive mosquitoes; vector-borne bacteria.

Figure 1

(A) Natural foci of tick-borne encephalitis in Croatia, 1960–2007 (places with documented human infections); (B) geographical distribution of human tick-borne encephalitis cases, 2017–2022 (shadowed areas represent counties with reported cases, red dot represents a cluster of TBE cases in a new micro-focus); (C) seasonal distribution of tick-borne encephalitis cases (number of reported cases by month).

Figure 2

Distribution of acute WNV infections in humans and animals in Croatia, 2012–2022. Shadowed areas represent counties with reported infections; black silhouettes represent host species with WNV infections.

Figure 3

Distribution of Usutu virus in Croatia. Shadowed areas represent counties with reported infections; black silhouettes represent host species with acute clinical infections or USUV RNA detection; blue silhouettes represent species with serologic evidence of USUV infection (detection of neutralizing antibodies).

Figure 4

(A) Distribution of Tahyna orthobunyavirus in humans and animals in Croatia, 2017–2022. Shadowed areas represent counties with serologic evidence of TAHV infections (detection of neutralizing antibodies); black silhouettes represent host species seropositive to TAHV; (B) Counties with large presence of Aedes vexans mosquitoes.

Figure 5

(A) Counties with reported Bhanja virus seropositive patients, 2020–2022 (shadowed areas; (B) places with Haemaphysalis punctata tick records (numbers represent locality labels).

Figure 6

Seasonal and geographic distribution of Lyme borreliosis in Croatia (2011–2020): number of reported cases by month (A) and county (B).

Figure 7

Distribution of Ixodes ricinus ticks in Croatia (black dots represent places with records). Geographic coordinates (altitude-latitude, UTM) are presented in the Supplementary Table S1.

Figure 8

Reported cases of human leishmaniasis in Croatia, 2010–2020.

Figure 9

Distribution of Aedes albopictus (A) and Aedes japonicus (B) in Croatia, 2016–2020. (A): red shadowed areas represent counties with positive records, yellow shadowed areas with negative records, and gray shadowed areas—no data. (B): Purple shadowed areas represent counties with positive records, yellow shadowed areas with negative records, and gray shadowed areas—no data.