The reservoir hosts of Schistosoma japonicum in the Philippines and their role in transmission of Schistosomiasis

As a developing tropical country, the Philippines is endemic for a number of parasitic helminth species including Schistosoma japonicum, the major causative agent of schistosomiasis in Asia, the tapeworms Taenia saginata, T. Solium and T. asiatica, and a number of soil-transmitted helminths (STH), including Ascaris lumbricoides, Necator americanus, Ancylostoma duodenale and Trichuris trichiura. In the Philippines, 6.7 million individuals live in areas endemic for S. japonicum and 1.8 million are considered directly exposed to potential infection through their daily lifestyle and contact with water, including farming and fishing. Schistosomiasis japonicais a zoonosis and the causative parasite can infect up to 46 species of mammalian hosts, including humans and bovines. In China water buffalo have been identified as a major reservoir host, contributing up to 75% of human infection while in the Philippines, water buffalo (carabao), have been reported generally to be of less importance in transmission there, possibly due to the past use of insensitive diagnostic tools. In addition to S. japonicum, high prevalence of Fasciola gigantica has also been reported in bovines in the Philippines. Previous studies have suggested potential cross-protection between F. hepatica and S. mansoni. Anecdotal evidence had indicated that cross-protection may be occurring in the Philippines between S. japonicum and F. gigantica. STH are a common problem in many countries with 2 billion people estimated to be infected globally, with 1 billion infected with A. lumbricoides alone. The Philippines has the second highest rate of STH infections in Southeast Asia, where one third of the world’s STH cases occur. Poor hygiene is the major cause of STH infection and in Northern Samar, where the majority of the fieldwork for this thesis was performed, there are very few toilets or running water and electricity is intermittent; and in at least one of the study barangay, non-existent. As a result STH are endemic and a major cause of disease. Tapeworm infections also result from poor hygiene and sanitation as well as contaminated, under-cooked infected meat. With a high prevalence of STH and tapeworms, co-infections are also common. Co-infections of certain helminth species, including co-infections of hookworm and S. japonicum have been known to cause an increase in anaemia than would be seen with a single infection of either parasite. To examine the role of bovines in transmission of S. japonicum in the Philippines further, a new diagnostic method - the Formalin Ethyl Acetate Sedimentation technique (FEA-SD) - and a real-time PCR (qPCR) assay were used to examine samples from 200 bovines, including both cattle and carabao. The Kato-Katz (KK) technique and qPCR were used to examine 560 humans from 6 barangays in Northern Samar. High prevalence of S. japonicum was found using the qPCR and FEA-SD in both cattle (87.5% and 77.1% respectively) and carabao (79.1% and 55.2% respectively) from all barangays surveyed. On average the daily egg output for each bovine was calculated at 195,000. High prevalence of S. japonicum was likewise found in humans using the qPCR technique (90.2%). A high prevalence and infection intensity of F. gigantica was also found in the bovines by qPCR and FEA-SD (95.3% and 96.0% respectively). No correlation was found between egg counts of either species that would indicate any cross-protective effect. A multiplex qPCR was performed on a subset of 163 humans from two barangays originally examined for S. japonicum infection to determine the level of co-infections of STH, tapeworm and S. japonicum infections in Northern Samar. High levels of co-infection were found, with the majority of individuals infected with three or more species of helminth worm. The major objective of this thesis was to determine whether bovines, both cattle and carabao, are important in transmission of schistosomiasis in the Philippines, with the unprecedentedly high prevalence in bovines, both cattle and carabao, shown by both qPCR and FEA-SD confirming this hypothesis. Current control methods rely on mass treatment programs that have high non-compliance. Identification of a major reservoir host for S. japonicum in the Philippines presents a new control avenue with the treatment of animals with praziquantel or the introduction of a veterinary vaccine as part of an integrated control program.