In recent years, VIS* have become a valuable tool for accelerating the evaluation of promising new drugs. In a tightly controlled environment, volunteers receive a low number of drug-sensitive malaria parasites (sporozoites) and the level of parasitaemia in their blood is monitored closely. Around 7 days later, the volunteers receive the experimental drug candidate, while parasitaemia continues to be monitored. In this way, these studies enable us to understand quickly whether a compound will be efficacious against malaria and guide dose selection for subsequent clinical studies. VIS can also be used to look at how molecules work in combination, informing the selection of optimum partner drugs, the potential interactions between them and their dosages.
*Formerly known as the controlled human malaria infection (CHMI) model
VIS for blood-stage and transmission-blocking activity
VIS are also being used to explore the activity of experimental drugs against the sexual (gametocyte) stages of the malaria parasite to assess transmission-blocking activity and thus be used to assess the transmission-blocking activity of new molecules coming through the pipeline from drug discovery. The simplest way is to also monitor the development of gametocyctes at the same time blood-stage parasitaemia, as described above.
VIS for chemoprotection/chemoprevention
In these studies, the volunteer receives a dose of the experimental drug before being infected with sporozoites. The length of time between drug administration and parasite inoculation can vary to determine activity and to predict the frequency of administration required for chemoprevention. Following the inoculation of sporozoites, parasitaemia is monitored from day 6 onwards and rescue medication is given as needed, or on day 28. These studies enable us to assess the potential of the drug to protect against infection in humans and allows for side-by-side comparisons of drug candidates.
Learn more about how volunteer infection studies are being used in an interview with MMV's Jörg Möhrle.