*3.2.3.1 Candida auris*

*Candida auris* is an emerging pathogenic yeast belonging to the genus Candida and is responsible for multidrug-resistant invasive infections in nosocomial settings [141–143]. The species has been mainly isolated from nosocomial environment, where it survives for a long time and can form biofilms resulting in inter and intra-nosocomial transmissions [141, 142, 144]. *Candida auris* was first identified in 2009 in Japan and has rapidly spread to five continents (North America, South America, Europe, Asia and Africa) becoming an International Health Security threat [143, 145]. *C. auris* infections has been identified in Australia, Bangladesh, Kuwait, India, Japan, Pakistan, Oman, Singapore, Iran, Panama, Venezuela, Colombia, Brazil, Chile, United States, United Kingdom, Spain, Germany, Israel, France, and the Netherlands [141–143]. The emergence of *C. auris* has been attributed to widespread usage of antimicrobial (antibiotics and antifungal) agents and rising ambient temperatures [141]. *C. auris* results in skin or mucosal colonization in patients with the organisms being recovered from physical surfaces such as furniture, medical equipment or sinks [141, 142]. No animal or environmental reservoir for *C. auris* has yet been identified. Previous [141] studies done in the United Kingdom, India and United States suggest community transmission and community reservoir are unlikely [141]. However, *C. auris* has a very efficient person-to-person transmission that allows it to spread rapidly among patients [141, 142, 144]. The person-to-person transmission and presence of yeast on surfaces suggest a potential respiratory droplet mode of transmission but no specific mode of transmission has been established yet [141, 142].

One unique feature that differentiates *C. auris* from other *Candida* spp. is its ability to cause invasive infections in individuals with normal neutrophil counts [144]. This is due to the reduced activity of human neutrophils against *C. auris* leading to poor outcomes [144]. Individuals requiring multiple medical procedures that results in prolonged hospital stay such as surgical procedures, cardiac catherization, endoscopic gastrotomy tube insertion and mechanical ventilation are at higher risk of *C. auris* infections [146, 147]. Infection or colonization with *C. auris* is also found frequently in patients with co-morbidities such as chronic/acute renal failure, immunosuppressive conditions/diseases, cardiovascular diseases, liver disease, diabetes mellitus and benign/malignant solid tumors [148]. The *C. auris* yeast exhibits a high range of antifungal resistance with resistance to fluconazole as high as 93% [141, 142]. Amphotericin B has a wider range of MIC and thus are less likely to be used as empirical therapy. Echinocandins has a more favorable susceptibility making it the drug of choice for *C. auris* infections [141, 142].

The lack of knowledge related to any animal reservoir makes the *C. auris* pathogen currently in stage-5 (exclusive human agent) of pathogen evolvement. The combination of drug resistance, persistence on environmental surfaces, reduced neutrophil effectiveness, and rapid person-to-person transmission has resulted in increased nosocomial outbreaks around the world with significant mortality and morbidity [141, 142, 144]. Currently, these outbreaks are limited to nosocomial settings and thus are in Phase-3 of WHO Pandemic alerts. These factors of rapid transmission, outbreaks in widespread geographical regions and reduced human neutrophil activity makes *C. auris* a huge potential International Health Security threat in case of sustained community outbreaks.

#### **4. Conclusions**

Since ancient times, large number of pathogens (viruses, bacteria, parasites, fungi) found in the environment are responsible for causing severe morbidity and mortality. These pathogenic organisms mainly infect humans through respiratory droplets, aerosols, dust, vector bite, contaminated food or water, or direct contact with animal hosts. The emergence of SARS-CoV-2 in 2019 and its global spread resulted in the announcement of the sixth public health emergency of international concern in last 10 years after Influenza A (H1N1) in 2009, Ebola virus in 2014, Polio in 2014, Zika virus in 2016, and Ebola in 2019 [68]. Moreover, in the last 20 years the emergence of novel pathogens such as SARS-CoV-1, MERS-CoV, Candida auris, and drug resistant bacteria in addition to the ongoing epidemics/ local outbreaks of vector-borne diseases such as Crimean-Congo Hemorrhagic fever and Zika has raised International Health Security alarms. This chapter mainly concentrates on the epidemiology, pharmaceutical tools, prevention, and control of pathogens having respiratory or vector mediated transmission. Infectious diseases continue to be major causes of fatality worldwide despite the significant advances in civilization, scientific technology, and medicine. On the contrary, these same advances may contribute to the emergence, re-emergence, and rapid spread of diseases due to climate change, deforestation, globalization, and over usage of pharmaceutical tools. In the last few decades, the rapid emergence/re-emergence of novel and resistant pathogens make it essential to establish surveillance and research programs into potential pandemic causing pathogens. It is important to take cognizance of the hazards posted by these vector-borne and airborne pathogens, already circulating among the animal or human population to prevent the risk of epidemics and global pandemics. Majority of the viruses with potential to cause pandemics lack antivirals and vaccines while fungi and bacteria have developed resistance to antimicrobials. Thus, special attention needs to be paid in the research and identification of effective drugs against these pathogens to have the medical countermeasures available to fight future pandemics and protect our International Health Security.

*Which Plagues are Coming Next? DOI: http://dx.doi.org/10.5772/intechopen.96820*
