# Emergent and Known Honey Bee Pathogens through Passive Surveillance in the Republic of Kosovo
## 1 Introduction  
Honey bee health has recently become a major topic due to the important role that bees play in pollination and food production [1]. In the last ten years, some regions of the world have suffered from a significant reduction in honey bee colonies [2]. It is believed that the reduction in honey bee populations is caused by a number of different biotic and abiotic factors, in particular pests, genetic factors, bee management, including beekeeping practices and breeding, climatic changes, malnutrition, agricultural practices, and the use of pesticides [2]. From emergent bee pathogens, the microsporidian species _Vairimorpha_ (formerly _Nosema_) _apis_ and _Vairimorpha_ (formerly _Nosema_) _ceranae_[3] have been identified in European honey bees, _Apis mellifera_. _V. ceranae_ is the most common gut pathogen in adult honey bees [4] and its infection could induce a degeneration of gut epithelial cells [5], a significant reduction in honey production [6], and a reduction in bee lifespan [7; 8; 9; 10]. Two trypanosomatids _Lotmaria passim_ and _Crithidia mellificae_ (Kinetoplastea: Trypanosomatidae) are capable of colonizing the digestive tract of honey bees [11; 12]. Bothpathogens are considered to alter bee physiology, behaviour, immune responses, and lifespan [13; 14; 15; 16]. Several bee viruses, like acute bee paralysis virus (ABPV), black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), Kashmir bee virus (KBV), Sackrood virus (SBV), and Israeli acute paralysis virus (IAPV) have been documented to be transmitted and activated by _Varroa_ mites in field conditions [17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. ABPV, BQCV, KBV, and IAPV belong to the _Dicistroviidae_ family [28] while DWV and SBV are classified in the _flavouridae_ family [28]. CBPV has not yet been classified into any taxa [29]. ABPV and IAPV cause trembling, inability to fly, rapidly progressing paralysis, and death of honey bees [30; 31; 32], whereas KBV in natural infections commonly persists within apparently healthy breeds and adults [33; 34; 35]. CBPV causes massive worker bee losses, mostly in strong colonies, and its infection appears in two groups of clinical signs: one including inability to fly, clustering, trembling, and crawling; the other consisting of black hairless individuals with shortened abdomens [36]. BQCV and SBV are the most widely distributed of all honey bee viruses. BQCV does not cause visible symptoms in infected adult bees but it could lead queen larvae and pupae to death by turning their cells black. Two-day-old larvae appear to be most vulnerable to SBV infection and, once they are fed with contaminated larval food, they fail to pupate [37; 38], acquiring a sac-like appearance. DWV causes deformed wings in honey bees and induces colony weakening and mortality. Typical disease symptoms of DWV infection include shrunken, crumpled wings, decreased body size, and discoloration in adult bees. Three genetic variants of DWV were discovered and identified as types A, B, and C, but DWV-A and -B are the most widespread variants [39; 40]. Two bacterial pathogens affecting honey bee larvae but not adult bees are _Paenibacillus larvae_, the causative agent of American Foullbrood (AFB), and _Melissococcus plutonius_, responsible for European Foulbrood (EFB) [41]. The clinical symptoms of AFB are darkened, sunken, and perforated cell caps containing diseased larvae, a characteristic unpleasant odour, and sticky larval remains when drawn out with a matchstick. Instead, EFB usually affects young larvae that die while still coiled before they are capped. The younger larvae affected cover the bottom of the cell and are almost transparent, with a visible trachea and midgut; the latter, full of bacteria, appears as a yellow spot. Dead, flacid discoloured larvae in uncapped cells show colour changes from pearly white to yellow to yellowish brown [42]. AFB and EFB are both widely distributed and potentially lethal to infected colonies [41; 42; 43; 44].