The amphibian population is important in the ecosystem to maintain a stable environment. Amphibians like frogs control the insect population and are indicators of quality of the surrounding environment (Bernardo-Cravo et al., 2020; Rahman and Shakinah, 2015). Amphibians are sensitive to environmental changes in both terrestrial and aquatic habitats because they have highly semi-permeable skins and different life-cycle stages (Alford and Richards, 1999). If there are many frogs in an area, it shows a healthy environment which a frog die-off indicates a problem with the water, air or soil in their habitat. Unfortunately, the population of frog is declining at a rapid rate throughout the world (Ceballos et al., 2017; Collins and Storfer, 2003). About 40% of global amphibian populations are declining due to dwindling habitats and a rise in infectious diseases. Several factors have contributed to the rapid decline in the frog population, including diseases caused by pesticide pollution, parasites and habitat loss (Blaustein et al., 2018; Hayes et al., 2010). Pesticides exposure might weaken the immune system (Brown et al., 2021; Rohr et al., 2008) and cause limb malformations in frogs (Kiesecker, 2002). According to Sparling and Fellars (2009), exposure to chlorpyrifos and endosulfan poses a serious risk to amphibians in the Sierra Nevada mountains, as these insecticides affect acetylcholinesterase activity in amphibians. However, Bradford et al.(2011) did not support the hypothesis that pesticides have contributed to the population decline of Rana muscosa and R. sierrae in the Sierra Nevada mountains. Besides pesticide contamination, pathogenic parasites can also affect the anuran health state and cause mortality (Hua et al., 2017). Frogs are known as hosts to different types of protozoa, such as blood parasites. Research in Malaysia related to blood parasites in frogs is scanty, and none of the studies have shown correlation between pesticide usage with the abundance of blood parasites.

Metsulfuron methyl decreases acetylcholinesterase activity (Pretto et al., 2011) and shows similar effect as insecticides (chlorpyrifos and endosulfan)(Sparling and Fellers, 2009). Acetylcholinesterase activity in brain and white muscle of teleost fish decreased significantly (p< 0.05) after exposure to commercial formulations containing metsulfuron methyl when compared to control values (Pretto et al., 2011). However, pesticide usage has increased in agriculture, and this may affect the persistence and health of amphibian population. Amphibians found in agricultural areas may be exposed to toxic effects of pesticides and the pesticides used not only affect the frog population, but also affect the parasites in the frogs (Bruhl et al., 2013). Bruhl et al.(2013) studied the effects of pesticide products on juvenile European common frogs and found that the mortality of juvenile frogs decreased by 40% after one week. Hua et al.(2016) proved that insecticides reduced cercariae growth in frogs but not in a dose-dependent manner. Therefore, knowledge of