The World Health Organization (WHO) estimates that 120 million people in tropical and subtropical areas of the world are infected with W. bancrofti
or Brugia malayi
; most are asymptomatic. Almost 25 million men have genital disease, and 15 million people, the majority of whom are women, have lymphedema or elephantiasis of the leg.3
The WHO and local experts believe that hydrocele is the most common manifestation of filariasis in men.3,4
The WHO uses prevalence of hydroceles as a measure of effectiveness of filaria eradication programs.3,5
Surgical treatment of hydroceles is often difficult to acquire in endemic areas because of poor health care infrastructure. Untreated hydroceles become massive, disabling the patient and startling visiting medics. Failure to treat hydrocele in childhood will result in a high prevalence of the condition. Colocation of endemic filariasis with prevalent massive hydroceles has linked the 2 in a cause-and-effect relationship. While it is to be expected that a high percentage of male patients with hydrocele would be positive for filaria, the rate is not much different to background infection rates in endemic areas.6
Several studies have shown that almost half the patients with tropical hydrocele in endemic areas, before eradication programs, do not have evidence of infection with filaria.6,7
Mass drug administration has been used as part of a global project to eliminate lymphatic filariasis. Recently this has included the use of DEC-fortified cooking salt, which is effective against adult and larval forms of the parasite and is thought to have been responsible for the eradication of lymphatic filariasis in China.8
The program has been particularly successful in Léogâne, where we found DEC-fortified salt to be commonly used.9
Despite an almost complete elimination of elephantiasis in Léogâne (the 2 patients seen were in remote villages not receiving DEC), hydroceles remain a very common affliction. Because of limited resources, we had to reserve surgery for adults with massive hydroceles that limited mobility or for children. We found a persistent processus vaginalis in almost all of these patients. Hydroceles in this area, and probably tropical hydroceles in general, are more likely to be due to a persistent patent processus vaginalis than to persistent filariasis. This is the mechanism of hydrocele formation in the developed world where treatment is usually carried out in childhood. There is probably little difference between hydrocele in developed countries and tropical hydrocele other than neglect. The epithet “tropical” more properly refers to the social condition of the area rather than a specific pathogenesis of the hydrocele.
Failure of neonatal obliteration of the processus vaginalis is a mechanism for both inguinal hernia and hydrocele development. Persistence of smooth muscle in the peritoneal tissue of the processus vaginalis has been shown in patients with hernias or hydroceles but not in the peritoneum of patients without hernias or hydroceles.10
Immunohistochemistry shows these smooth muscle cells to be in an intermediate state of differentiation, suggesting that a drive to apoptosis, which would have resulted in obliteration of the processus vaginalis, was interrupted.11
There is no reason to believe that these mechanisms would be any different in the tropics or that they would be influenced by filariasis.
Elephantiasis has been known to man since ancient times, but was confused with leprosy until the work of Avicenna in the 11th
Little progress was made until the mid-19th
century, when Otto Wucherer (Brazil, 1868) and Timothy Lewis (India, 1872) independently demonstrated the presence of filarial worms in chylous urine.12
Patrick Manson, working in China in 1885, realized that filaria were responsible for elephantiasis of the scrotal skin.12
In 1877, Joseph Bancroft added hydrocele to the list of conditions caused by filaria.12
The causative role of filariasis in tropical hydrocele became dogma in the shadow of these giants of tropical medicine, all of whom could find evidence of filaria in chylous urine, but not in hydrocele fluid. More recently, disruption of lymphatics and abnormal connection to the renal pelvis have been shown by lymphangiography in patients with filarial chyluria.13
Prior to filaria eradication programs, chylous fluid was sometimes found in hydroceles. This was most likely due to abnormal connections between blocked mesenteric lymphatics and peritoneum in patients with chylous ascites that communicated with the scrotum.4
We did not find chyle in any of the hydroceles or ascites in our patients, who came from an area where filaria eradication programs have been successful.