Epidemiology of zoonotic and neglected tropical diseases in the Lao People’s Democratic Republic

Abstract

Laos is one of the poorest and least developed countries in Southeast Asia and living conditions, livestock production and cultural practices place large proportions of the population at risk of exposure to a range of parasitic and viral zoonoses. Surveys of humans, pigs and dogs were conducted to determine the prevalence of and risk factors associated with the transmission of Taenia solium and related Taenia species, Trichinella spp., soil-transmitted helminths (STH), and viral zoonoses including Japanese encephalitis virus (JEV), hepatitis E virus (HEV), swine influenza virus (SIV) and Nipah virus (NiV). Surveys were conducted in villages and slaughterhouses in four ethnically diverse provinces of northern Laos. The human, pig and dog populations studied had a very high prevalence of parasite infection and zoonotic transmission between humans and animals was apparent for multiple species including taeniaisis/cysticercosis, trichinellosis and hookworms. Cysticercosis in the human population was relatively rare with a prevalence of less than 2%, although a focal distribution and concentration of cases in a small number of villages was evident. Taenia saginata was the dominant Taenia species infecting people and T. hydatigena was the dominant species infecting pigs. Trichinella spiralis was the only species detected in pigs and we found serological evidence that human exposure to Trichinella larvae was common. STH infections were very common and the poorest members of the survey population and people of the Mon-Khmer ethnic group were at greatest risk of having an STH infection. JEV was identified as being hyper-epizootic in northern Laos and remains an unmanaged threat to human health. The hemagglutination inhibition seroprevalence of JEV in the pig population was 74.7% and IgM seroprevalence of 2.3 % peaked in the monsoonal wet season months. Seroprevalence of HEV was 21.1% and the molecular characterisation of HEV isolates from village pigs demonstrated genetic homogeneity with human HEV isolates from China. \ud This thesis presents new data on a wide range of neglected tropical diseases, ranging from parasitic infections associated with poverty and poor sanitation through to non-discriminating zoonotic viruses. The zoonotic and neglected tropical diseases circulating in Laos are, undoubtedly, a major burden on public health and wellbeing and initiatives to prevent transmission are urgently required