DID INTENSIVE FLOODS INFLUENCE HIGHER INCIDENCE RATE OF THE WEST NILE VIRUS IN THE POPULATION EXPOSED TO FLOODING IN THE REPUBLIC OF SRPSKA IN 2014?

Climate change is defi nitely one of the greatest challenges of human development in the 21st century. Climate change is expected to increase the risk of communicable diseases in Europe. Th is impact will depend not only on local climatic conditions, but on other factors, such as current in-frastructure, public health services, biodiversity specifi city, etc. Th e population in Bosnia and Herzegovina, Croatia and Serbia has been severely af-fected by the fl oods caused by cyclone Tamara in 2014. Th e basic mode of transmission of the disease caused by the West Nile virus is the bite of the infected mosquito. Th e West Nile virus is not transmitted among humans through contact, nor can it be transmitted from infected birds to humans without mosquito bite. Th e aim of the study was to analyze and present the trend of this disease in the period 2014-2018 and to show the connection between the spatial occurrence of cases and location of the fl ooded area in 2014 in the Republic of Srpska. Using the descriptive method, the demographic data of the patients were analysed, analysed. Th e cases were mapped and we analysed the connection of the case and location that was fl ooded. Th e incidence ranged from 0.79 in 2014 to 0.43 in 2018. Patients were of all age groups and both sexes, most com-monly cases from rural areas (78%). Th e most common clinical form of the disease is shown, which were symptoms of the central nervous system infection. Out of the total number of patients, 94% were from fl ooded areas. All reported cases have been diagnosed at the Institute of Microbiology at the University Clinical Center of Republika Srpska and were reported as probable cases in accordance with the international case defi nition of communicable diseases. However, it is crucial to implement internationally endorsed procedures as a clinical alghoritm for the confi rmation of the case in accordance with the laboratory criteria for the case defi nition. Th e occurrence, frequency and spatial distribution of cases indicates a possible connection with the fl oods in 2014.


INTRODUCTION
A recent study by the European Center for Disease Prevention and Control has found that vector-borne diseases are one of the eight major communicable threats for Europe, along with the emergence and spread of resistance to antibiotics or pandemic infl uenza (Semenza et al., 2018). Climate changes aff ect the survival and transmission of arthropod vectors, as well as the rates of development of pathogens that are transmitted by the vectors. Th ere was a signifi cant correlation between mean temperature, precipitation and mosquito density (Lee et al., 2013). Th is resulted in the seasonal epidemics of West Nile fever in the countries across the Europe for which there is no eff ective control measure such as vaccine in humans. Even the availability of an equine vaccine did not prove to be a solution because the coverage was low, probably due to sporadic epidemics and the relatively high cost of vaccine for the owners (Findlater et al., 2018). Ambient temperature is one of the most important abiotic factors aff ecting the life of the insect. Mosquitoes, such as Aedes aegypti and Aedes albopictus, transmit many pathogens, including Denge, Chikungunye and Zika viruses. Th e spread of these diseases has become the main global health issue and it is predicted that the climate change will aff ect the distribution of mosquitoes, which will enable these insects to introduce new pathogens into sensitive populations (Reinhold et al., 2018). Due to the combination of anthropogenic changes, including eff ects on the global climate and migration of wild animals, there is strong evidence that the regions with a moderate climate have repetitive occurrence of mosquito-borne diseases, but also the emergence of those diseases that have not previously been detected through surveillance.
In Europe, the re-emergence of West Nile virus (WNV) and Usutu virus is associated with the bird migration from Africa, while the autochthonous transmission of Chikungunya and Denga viruses is fuelled by a combination of invasive mosquitoes and rapid transcontinental travel by infected people (Johnson et al., 2018). Arboviruses are a diverse group of viruses that are transmitted by the vectors, many of which cause signifi cant human morbidity and mortality. Continuous geographical expansion of the Dengue virus, along with explosive epidemics of the WNV, Chikungunya and Zika, served as a reminder that a new epidemics can occur at any time from this diversity. A clearer understanding of the mechanisms that trigger these dramatic changes in the transfer cycles from host to host that result in a signifi cant exposure of the human population will help us prepare for the next epidemic/pandemic (Young, 2018). Arboviruses such as WNV, Zika, Chikungunya, Dengue and Yellow fever have become very signifi cant global pathogens through unexpected, explosive epidemics (Rückert et al., 2018).
A constant occurrence is evident during summer months in Europe (from July to September) when higher ambient temperatures favor the activity of mosquitoes, while winter months (December to February) generally lead to cessation of their activity. Environmental studies in southern and northern Europe illustrate this, showing the highest number of species in the summer months. It is during these peaks of the season that the autochthonous transmission of the virus takes place and the occurrence of diseases caused by mosquitoes is observed. Th e autochthonous transmission of viruses in mosquitoes in Europe is dominated by the emergence of the number of exotic viruses. Th e best example of this is the re-occurrence of WNV, which is mainly transmitted by the mosquito species of the genus Culex. Th e epidemiology of the WNV is complex, and it consists of a cycle of infection between mosquito species that serves as a vector of the virus, wild birds acting as a reservoir and illness in humans and horses. Th e whole cycle must include populations of mosquitoes that bite birds and mammals. Examples of these populations include the Culex pipiens population (Vogels et al., 2016), especially those in southern Europe, as well as Culex modestus (Balenghien et al, 2008). Models that predict the time and location of human infection with Arboviruses have the potential to more eff ectively control mosquitoes and prevent disease. Th e objectives of this study were to analyze and present the occurrence and trend of the West Nile fever in the period 2014-2018, to analyze cases according to the place of residence and determine whether there was a higher incidence of the disease in the fl ooded area in 2014 as compared with the other parts of the Republic of Srpska, and to present a WNV case classifi cation of patients based on the diagnostic method and the case defi nition criteria.

MATERIAL AND METHODS
Using the descriptive method, the demographic data of the patients were analyzed, and the classifi cation of cases based on case defi nition were performed. Th e most common clinical forms of the disease and the incidence of the West Nile fever in the period 2014-2018 in the Republic of Srpska were described. All cases reported in the Republic of Srpska were mapped and we analyzed the correlation of the location of the case with the area aff ected by the fl oods. Also, each case has been monitored in terms of clinical course of the disease and the outcome of the treatment. Each case has been reported in accordance with the adopted case defi nition for West Nile fever of the European Center for Disease Control, which is obligatory to be applied in accordance with the current Regulations on the manner of reporting, the contents of records and the content of the notifi cation of infectious diseases (Offi cial Gazette of the Republic of Srpska 07/19). Th e case can be classifi ed as possible -probable -confi rmed on the basis of the case defi nition criteria. • Clinical criteria: any person with a high fever or at least one of the following two criteria: encephalitis, meningitis. • Laboratory criteria: A laboratory test for case confi rmation implies at least one of the following four criteria: -Isolation of WNV from blood or liquor, Arhiv veterinarske medicine, Vol. A laboratory test for a probable case is the antigenic specifi c response to WNV in serum.
• Epidemiological criteria: at least one of the following two epidemiological links: -Transfer from animal to human (permanent or shorter stay or exposure to mosquitoes in areas where WNV is endemic in horses or birds), -Transfer from person to person (vertical transmission, blood transfusion, transplants).
Aft er clinical and epidemiological criteria were confi rmed, a sample of blood was taken from each patient and tested for the presence of IgM and IgG antibodies using ELISA according to the manufacturer's instructions (Euroimmun, Germany) at the Institute of Clinical Microbiology at the University Clinical Center of Republika Srpska (UCC RS). Each patient has been monitored in terms of clinical course and outcome.

RESULTS
In the period 2014-2018, a total of 18 cases of West Nile fever were reported. Th e incidence ranged from 0.79 in 2014 to 0.43 in 2018, which clearly corresponds with large fl oods that aff ected the Republika Srpska in 2014 (Figure 1). Based on a descriptive analysis, the data showed that the average age of patients in the observed period was 51.7 years. Th e youngest patient was 6 and the oldest one was 87 years old, but there was no statistically signifi cant diff erence in the number of patients between diff erent age groups. Th e results of the χ ^ 2 test (χ ^ 2 = 3.556; p = 0.096) showed that there was no statistically signifi cant diff erence (p <0.05) in the number between male and female patients. Based on the statistical analysis, it was concluded that there was a statistically signifi cant diff erence in the number of patients by the type of settlement in which they lived. Statistically signifi cant (p = 0.018 <0.05) was the higher number of patients living in the rural area as compared to the number of patients living in the urban area, exactly 76% of them.  Of the total number of patients, 94% were from the fl ooded areas belonging to the municipalities of Šamac, Derventa, Modriča, Prijedor, Novi Grad, Banja Luka, Teslić, Petrovo, which corresponds exactly to the map of the areas that were aff ected by catastrophic fl oods in 2014 (Figure 3). Out of all cases, 90.9% were reported in June and July 2014, that is, less than a month or two aft er the fl ood. Th e most common clinical form of the disease was neuroinvasive infection with a fever and meningoencephalitis (100%), which fully meets the criteria of the case defi nition of this disease. All reported cases have been tested at the Department of Microbiology (UCC RS) with a positive fi nding of serum IgM and IgG antibodies and are reported as probable cases in accordance with the international case defi nition of this infectious disease. All patients were dissmised completely recovered.

DISCUSSION
Since its discovery in 1937, WNV has spread beyond its original geographical area and has caused disease on all continents except in Antarctica. Th e main goal of the West Nile fever control in the human population is to continuously monitor the epidemiological, clinical and virological characteristics of the WNV in order to take appropriate measures to prevent and control the spread of the disease. Reported cases of illness and/or deaths from the West Nile fever neuroinvasive form in the human population are the most accurate indicators of the activity of the WNV in humans. It is necessary to evaluate potential risk factors for infection and possible transmission within a period of three weeks before the onset of symptoms of the disease. Th e case of West Nile fever should be suspected in people over 50 years of age presenting with encephalitis or meningitis in the summer or early autumn months. Restricting the blood donation should be considered in areas where this virus is circulating. Th ere are specifi c rules in the EU that address the safety of blood by delaying voluntary donations of 28 days aft er leaving the area in which there is a transmission (EU Commission Directive 2004). Th e epidemiological situation of the disease in Europe is heterogeneous: some countries report epidemics in humans and animals every year, while others have never reported any autochthonous cases. Th e concept of "One Health" recognizes that the health of people, animals and the environment is interconnected and that only a collaborative interdisciplinary approach can eff ectively achieve optimal health outcomes (Lerner et al., 2015).
Aft er the catastrophic fl oods that aff ected the Republic of Srpska in 2014, on May 26, 2014, a Webex conference was held with the representatives of Bosnia and Herzegovina, Croatia and Serbia, the World Health Organization and the European Center for Disease Control. Th e aim of the meeting was to discuss on necessary measures to prevent the outbreak of diseases that are transmitted to the vectors. Th e main risk identifi ed as a threat to human health is the epidemic of the WNV.
Th e fi rst case of West Nile fever has been reported to the Institute of Public Health of the Republic of Srpska on 10 June, 2014. Th is fi rst-reported case was from the Banja Luka area, followed by cases from the municipalities of Novi Grad, Teslić, Derventa, etc. All patients were hospitalized on the basis of relevant clinical symptoms and some were later transferred to further diagnostics and treatment to the University Clinical Center of the Republic of Srpska in Banja Luka. Since all sera of the patients were tested positive for IgM and IgG antibodies using the ELISA, they were all classifi ed as a probable cases. However, University Clinical Center of the Republic of Srpska doesn't sample cerebrospinal fl uid for confi rmation of the cases, which is a weak spot in the management of the cases and surveillance of the disease. Th erefore, this procedure should be implemented in the future according to the European Center for Disease Control case defi nition for confi rmation (Hrnjakovic . Th is is very important for distinguishing WNV from tick-borne encephalitis and other arboviral infections as they have very similar clinical manifestations (Petrovic et al., 2018). It is important to emphasize that this is a passive surveillance and there were no intensive measures to detect cases using diff erent procedures than usually. Th e increase of incidence was not the consequence of active surveillance and tracing of the cases. One of the factors that might have infl uenced such condition was the fact that the population from the fl ooded area spent more time outside, repairing the damage aft er the fl oods and working around artifi cial water ponds.
Th Monitoring of the disease in humans focuses on early detection of cases and identifi cation of aff ected areas aimed at the implementation of relevant measures including safety standards for blood transfusion, vector control and communication with relevant institutions and the public. Th is is particularly challenging because most cases are asymptomatic, which is a particular risk in aspects of blood and organs donations.
Th e integration of surveillance and surveillance activities carried out by the public health authorities, animal health care institutions and institutions responsible for vector control and surveillace should enhance effi ciency and save resources by targeted measures (Gossner et al., 2017).

CONCLUSION
In the period 2014-2018, the highest incidence of West Nile fever was recorded in 2014 when the Republic of Srpska was aff ected by the fl oods. All hospitalized and analysed patients had neuroinvasive disease. Most cases were registered in fl ooded areas mainly among rural populations. It is necessary to perform more analyses in close cooperation with the veterinary sector to establish and confi rm the interconnection between disease cases, fl oods and infected mosquitoes in the fl ooded area. All cases are classifi ed as "probable cases"; however, it is crucial to implement internationally endorsed procedures as a clinical alghoritm for the confi rmation of the case in accordance with the laboratory criteria for WNV case defi nition.