Plasmodium falciparum
Plasmodium falciparum is a unicellular protozoan parasite of humans, and the deadliest species of "Plasmodium" that cause malaria in humans. It is transmitted through the bite of a female "Anopheles" mosquito. It is responsible for roughly 50% of all malaria cases. It causes the disease's most dangerous form called falciparum malaria. It is therefore regarded as the deadliest parasite in humans, causing 435,000 deaths in 2017. It is also associated with the development of blood cancer (Burkitt's lymphoma) and is classified as Group 2A carcinogen.
Varroa
"Varroa" mites are recognised as the biggest pest to honeybees worldwide due to their ability to transmit diseases such as deformed wing virus (or dwv) to larval or pupating bees, resulting in death or severe deformity of the pupae.