Malaria remains one of the most widespread infectious diseases of our time. The latest estimates reveal that ~250 million people are infected with malaria across the globe, of whom ~800,000 die every year 
, the vast majority being young children. In 2007, the malaria eradication agenda was adopted by many researchers in the antimalarial community and target product profiles for new antimalarial medicines were defined 
. Most available antimalarials were designed to target the pathogenic blood stages in humans and to address the constant threat of drug resistance 
. However, to meet the objective of malaria eradication, medicines that block parasite transmission 
and eliminate the asymptomatic and sometimes cryptic hepatic forms also need to be developed. The bottleneck populations of liver and sexual stage parasites 
represent potential pathogen vulnerabilities that could be targeted by small molecules; the first such bottleneck is at the liver stage. Within minutes of being released by the bite of an infected female Anopheles
sporozoites reach the mammalian liver, where they invade hepatocytes and either lie dormant or develop over several days, eventually forming the schizonts that are the prelude to a blood stage infection 
. Molecules that efficiently target the parasite stages in the liver would offer protection from infection and could theoretically eliminate the cryptic hypnozoite (dormant parasite) infection reservoirs formed by P. vivax
and P. ovale
. Because only 100 or so sporozoites may be introduced by a bite, there are likely to be many orders of magnitude fewer parasites at this stage than in an active blood stage infection, reducing the possibility of resistance arising. A second bottleneck occurs during sexual development. At each round of schizogony ~1% of merozoites differentiate into gametocytes 
, and it is these developmentally arrested cells that are transmitted to the mosquito. Mature gametocytes are sexually dimorphic, forming microgametocytes and macrogametocytes that escape the red blood cell (RBC) and produce male and female gametes in the blood meal of the mosquito by processes known as exflagellation 
and activation, respectively. Following fertilization the zygote differentiates into a motile and invasive ookinete within which the briefly diploid genome undergoes meiosis. These processes occur within an environment almost totally derived from host blood, which can therefore provide a novel and ideal conduit for the delivery of drugs to inhibit parasite transmission to the mosquito. Having crossed the mosquito midgut wall 
, the very few surviving ookinetes differentiate into oocysts, which undergo endomitosis, eventually producing thousands of daughter sporozoites. The sporozoites migrate from the midgut of the mosquito to its salivary glands where the lifecycle begins again.
Given that it would be highly desirable for candidate drugs to have activity against hepatic and sexual forms of the malarial parasite, it is surprising that few clinical trials, to date, have examined whether gametocyte carriage can be reduced following drug treatment. The only drugs found to be effective at reducing gametocyte carriage include artemisinin 
, artemisinin combination therapies (ACTs) 
, methylene blue 
, and primaquine 
. Additionally, few studies have investigated the impact of drugs on the transmission of parasites from human blood to the mosquito vector 
, nor have many been designed to evaluate antihepatic stage activity. In the context of malaria eradication these gaps in our understanding of the full potential of the drug armoury are problematic.
Here we report the development of a series of novel assays against liver, sexual blood, and mosquito stages of the malaria parasite, using both drug-susceptible and drug-resistant parasite strains. We applied these assays to the current portfolio of schizonticidal compounds, consisting of 50 anti-infectives currently in use or under development..