The protective role for Human Adenovirus against water chemical disinfection of Acanthamoeba polyphaga.

Adenoviruses are important human pathogens that are responsible for both enteric illnesses and respiratory and eye infections. Recently, these viruses have been found to be prevalent in any kind of aquatic environment, such as rivers, coastal waters, swimming pool waters, and drinking water supplies worldwide. Acanthamoeba is the most common free-living environmental amoeba, it may serve as an important vehicle for various microorganisms living in the same environment, such as viruses. This study aimed to investigate the interaction between Human Adenovirus type 5 (HAdV 5) and Acanthamoeba polyphaga in water environment in order to highlight the role of protection from chemical disinfection of internalized viruses. In the first part of the study, Acanthamoeba polyphaga at mean concentration of 105 cells/ml was co-cultured in 24-well plates with Human Adenovirus (3.16 x 104 DCP50/ml) in water for 1 day at 25°C and the viral uptake was assessed by direct immunofluorescence. In a second series of experiments, the efficacy of sodium hypochlorite disinfection against Acanthamoeba and HAdV either singly, by cultural methods, or when co-cultured, as above method, was assessed. In particular, 3 different concentrations in water were tested: 5; 2.5 and 1 mg/L for 24 h contact time. The data obtained by the co-culture trials demonstrated that HAdV was incorporated into the host amoeba in water. In singly disinfection tests, the results revealed that amoebae still remained alive with 5 mg/L sodium hypochlorite while the viruses loss the infectivity with 2.5 mg/L. In co-cultured trials, at this disinfectant concentration, we found HAdV in Acanthamoeba polyphaga cytoplasm. The results of the study confirm and underline the possible role of protection of Acanthamoeba polyphaga for Human Adenovirus against chemical disinfection in water environment. More deeply studies in co-cultured experiments can clarify if HAdV infectivity is still present in amoebae after disinfection, revealing a new system of viral resistance in water environment.