Filariasis in Japan Some 25 Years after its Eradication

Japan is said to have eradicated filariasis some 25 years ago, but the exact time (and even the definition of eradication) is not clear. However, the results of successful control programs clearly indicate that the number of microfilaria carriers had been reduced to a very low level long before the “eradication”. As filariasis disappeared, the once stigmatized disease quickly lost clinical significance. At the same time, the number of parasitologists and researchers interested in filariasis dwindled quickly to only a handful in the whole country 10-15 years after the disappearance. Filariasis problems in Japan still remain as sequelae of the old infection. However, young clinicians have little knowledge of filariasis, and the rare, localized and non-lethal disease is disappearing also from the memory of doctors. On the other hand, some doctors continue to encounter cases of lymphedema, hydrocele and chyluria. Some of these are diagnosed as filarial in origin, and in most cases the diagnosis is based on the fact that the patients were born and brought up in the past endemic areas. Practically, there is no reliable way of diagnosing the old clinical filariasis. Some immunodiagnostic methods are available but they are not very specific. The purpose of this review is to describe what is happening with filariasis in Japan about 25 years after its eradication. The review will highlight the situation of chyluria, the most common sequela, and its treatment, recent filarial infections in Japan including imported cases and zoonotic filariasis, and immunodiagnostic methods used for suspected clinical filariasis.