Most of you should know elephantiasis - it's caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori, all transmitted by mosquitoes. The parasites occupies lymph vessels that drain the lower extremities, producing massive enlargement and deformity of the legs and genitalia. However, it is unclear whether the swelling results from the obstruction or from the immune response to the parasite and their endosymbiotic bacteria, Wolbachia, which I'll discuss later as horriible gender-bending parasites of many insects, but seems to be a both symbiote of filarial worms and the cause of their virulence.
Lymphatic filariasis currently affects around 120 million people in 80 countries. The Japanese artist Hokusai, who painted the "36 Views of Mt Fuji", also painted a Japanese sufferer who was wheeling his balls around in a wheelbarrow. (If you're ever in Tokyo, visit the Meguro Parasitology Museum. I could have gone to Disneyland or the Parasite Museum that day. Guess what I chose.)
Guinea Worm is another I'll cover later - it's the largest tissue parasite humans suffer.
River blindness, on the other hand, occurs when the microfilaria of Onchocerca volvulus migrate up into the skin or cornea waiting for blackflies. Your immune system response horribly blotches or scars your skin, eventually causing 'leopard skin' and blindness.
Loa Loa is a good one too - deer flies are the vector. The adults migrate all thru your body - scarring tendons, crippling joints, and best of all
The microfilaria, on the other hands migrate all thru your organs, spending most of the day in your lungs but gathering under your skin at dusk so the mosquitoes can drink them up. We don't know how they know, but it certainly makes diagnosis difficult if you take a blood sample at the wrong time of day. We know that heartworm in dogs (and as recently discovered, even worse in cats) does the same thing, and it's likely elephantiasis has a similar diurnal cycle.
There's a reason that these and so many other parasitic diseases of humanity, including Schistosomiasis, malaria,various tapeworms,african sleeping sickness, Marburg Virus, Ebola, Lassa Fever & too many other viruses to mention, originate in Africa - it's where we and our relatives evolved, and our parasites evolved with us.
Aren't we lucky that our parasites love us so...