Infectivity of Giardia duodenalis Cysts from UV Light-Disinfected Wastewater Effluent Using a Nude BALB/c Mouse Model

Giardia duodenalis is a protozoan of public health interest that causes gastroenteritis in humans and other animals. In the city of Campinas in southeast Brazil, giardiasis is endemic, and this pathogen is detected at high concentrations in wastewater effluents, which are potential reservoirs for transmission. The Samambaia wastewater treatment plant (WWTP) in the city of Campinas employs an activated sludge system for sewage treatment and ultraviolet (UV) light for disinfection of effluents. To evaluate this disinfection process with respect to inactivating G. duodenalis cysts, two sample types were investigated: (i) effluent without UV disinfection (EFL) and (ii) effluent with UV disinfection (EFL+UV). Nude immunodeficient BALB/c mice were intragastrically inoculated with a mean dose of 14 cysts of G. duodenalis recovered from effluent from this WWTP, EFL, or EFL+UV. All animals inoculated with G. duodenalis cysts developed the infection, but animals inoculated with UV-exposed cysts released a lower average concentration of cysts in their faeces than animals inoculated with cysts that were not UV disinfected. Trophozoites were also observed in both groups of animals. These findings suggest that G. duodenalis cysts exposed to UV light were damaged but were still able to cause infection. 1. Introduction Giardiasis is an intestinal infection caused by the protozoan Giardia duodenalis, and it represents the most commonly reported protozoan infection in humans and other animals. Some of the assemblage A and B subtypes of G. duodenalis have the potential for zoonotic transmission [1–3]. Cysts are the environmental stage of this organism, and they remain viable for several months under a range of environmental conditions and are extremely resistant to chemical disinfection. The infectious dose for these cysts is low; 10–25 cysts can cause illness [4]. Acquisition of giardiasis occurs through a faecal-oral route, which can be person to person, foodborne, or through contaminated water (drinking water or during recreational activities), with the last being the most significant means of transmission of this infection [5–7]. A large outbreak of giardiasis recorded in 2003 (Boston, MA, USA), exhibited two modes of transmission, which illustrated the capacity of G. duodenalis to spread through multiple means of transmission; these two modes included a common outbreak by exposure to contaminated recreational water and a subsequent prolonged propagation through interpersonal transmission between people in the community [4]. This pathogen was responsible for 132