Which of the following pathogens is not transmitted by a vector?

Step-by-step solution

Salmonella typhi (causal organism of typhoid) is transmitted by faecal oral route and not by a vector. The alpha viruses are transmitted by insect vectors, most commonly by mosquitoes. Plasmodium (malarial parasite) is transmitted by female Anopheles mosquito and Wuchereria bancrofti (filarial worm) is transmitted by female Culex mosquito.