It is widely accepted that the entomological inoculation rate (= EIR) is significantly correlated with the introduction of a patent infection with Plasmodium falciparum and other parasitic species. However, the question arose: how many sporozoites are needed to establish a patent infection? With respect to P. vivax in humans, it was published that as few as 10 sporozoites can be sufficient to establish a patent infection, while volunteer infections with P. falciparum showed that bites of five mosquitoes bearing more than 10 sporozoites are required to lead to a successful infection. These findings would indicate that in the case of P. falciparum, a higher rate of EIR is needed to spread malaria in a given region. In other coccidian parasites ( Eimeria , Toxoplasma, Sarcocystis , Isospora , Cryptosporidium, etc.), it is widely unknown how many oocysts are needed to establish a patent infection.