i agree with Dr. Monyer Al- fatlawi

As other infections, it depends on the number of parasites that have injected (number of mosquitos bites). Also, It depends on the individual immune system.

This has to do with worm load paradox wherein heavy work burden doesn't implies high morbidity. 

Multiple successful infective bites are required for establishing lymphatic filariasis infection

Parasite-host interaction factored by the number of worms injected into the host and host's level of immunity; for immunity varies and parasite load also varies amongst individuals, incidence should be expected to vary, with some coming down with the disease while others not.

Note: i. Interruption in transmission (less people bitten by insects, insecticide use).

           2. D =NV[H]/R (N=no.of parasites, V=virulence, H=hypersensitivity, R=resistance.

          3. Prophylaxis(use of filaricidal drugs)  

I will just add what seems to be missing in the debate and that is that cases might be under-diagnosed. The infection might not always be clinically apparent and such patients do not seek medical help and consequently dont get diagnosed. Also availability of diagnostic and healthcare services in affected areas might play a role.

Lymphatic filariasis can spread from person to person where people acquiring infected worms in their blood can infect others through mosquitoes bites. Nonetheless, not ALL people who were bitten by the mosquito carrying microscopic worms (microfilariae) will result in having Lymphatic filariasis. Because repeated successful mosquito bites over several months to years are needed to get lymphatic filariasis.

Additionally, hypothetically speaking time passes by the disease may become less deadly through developing immune response especially in endemic area.

Yes, almost everyone it at risk. It is actually spread from person to person by an infected-mosquito bites. Accdg to CDC, to acquire lymphatic filariasis a person has to be repeatedly bitten by an infected mosquito over several months to years.

There are several factors to be considered if we are going to look for the causes of acquiring lymphatic filariasis. First is the successful transmission through mosquito vectors, different mosquitoes has its own feeding and breeding behaviors which may be the cause as to why there only few cases found in an endemic area. Second is the health condition or the status of the immune system of the body, if it strong enough to fight the disease, acquiring lymphatic filariasis may not be possible as our body is sought to fight any foreign pathogenic organism that tries to enter our body.