The incidence of hepatitis a virus in selected water sources and associated risk of infection in South Africa

Abstract

Hepatitis A virus (HAV) is a non-enveloped, positively charged single stranded RNA hepatotropic agent from the family Picornaviridae, and the sole member of the genus Hepatovirus. There is only one HAV serotype but there are seven genotypes. Hepatitis A (HA) infection is usually self-limiting and the severity of the illness is age dependant. In children, infection with HAV is usually asymptomatic, while most adults and immunocompromised patients develop moderate to severe clinical disease. HA is endemic in South Africa (SA) with 100% of children from the lower socio-economic population acquiring immunity before the age of 10. With the current trends in urbanisation, a change in the epidemic vulnerability of the SA population can be expected. HAV is predominantly transmitted by the faecal-oral route and contaminated food and water are important sources of infection. However, the contribution of waterborne HAV to the burden of HA disease in SA is unknown. The aims of this investigation were to assess techniques for the recovery, isolation and detection of HAV from water sources. Thereafter these techniques were applied to estimate the potential risk of infection posed to communities using the water sources for recreational and domestic purposes. This would elucidate whether or not water plays a role in the spread of HAV infection in SA. An effective and sensitive concentration method is fundamental to the successful detection of HAV in water sources. Three primary recovery and two secondary concentration techniques were investigated in this study. An in-house modified glass wool technique, using 15g of glass wool and with the addition of three metal gauze grids at 5g intervals, proved to be the most sufficient and cost effective technique for the primary recovery of HAV from water sources. The packing density of the glass wool and positioning of the grids proved to be essential for efficient HAV recovery. A polyethylene glycol/sodium chloride secondary concentration technique proved to be more cost effective than commercial centrifugal devices. Combinations of cell cultures, propagation conditions, RNA extraction protocols and detection techniques were assessed for the isolation and detection of HAV. A combination of FRhK-4R cell culture propagation and reverse transcription-polymerase chain reaction-oligonucleotide probe assay was demonstrated to be the simple, most efficient technique for the detection of HAV. The nucleotide sequences of HAV strains from water sources and clinical specimens were compared to ascertain whether the strains from water were a potential source of infection. Although the majority of clinical strains clustered seperately from the water strains, one strain from an asymptomatic patient was identical to a number of strains from water. This suggests that HAV in the environment is a potential source of infection in SA. To assess the potential risk of infection constituted by HAV to persons using surface dam and river water for domestic and recreational purposes, a deterministic exponential risk assessment model which works with mean values and conservative assumptions was applied. Results indicated a minimal risk of infection to the higher socio-economic, non-immune population using the water for recreational purposes, if 100 ml of water was ingested per day. No risk was identified for the lower socio-economic, predominantly immune, population who uses the same water sources for domestic and drinking purposes. This study represents the first comprehensive data on risk of infection constituted by waterborne HAV in SA.