Which microfilariae are usually not found circulating in the peripheral blood?

Onchocerca volvulus is the correct answer because this type of microfilariae is primarily found in the skin and subcutaneous tissues rather than circulating in the peripheral blood. The adult worms live in nodules known as "onchocercomas," and when they release microfilariae, these larvae migrate into the skin where they can be picked up by the vector, typically a blackfly. This behavior contrasts with other filarial parasites like Brugia malayi and Wuchereria bancrofti, which are found in the blood and are transmitted by mosquitoes, as well as Loa loa, which is also found in the bloodstream where it can be collected by the vector, the deerfly. The life cycle and transmission modalities play a significant role in determining where these microfilariae can be commonly detected. Understanding the habitats and distribution of different larval stages is essential for diagnosing infections and managing filarial diseases effectively.