I was peering through back issues of Emerging Infectious Diseases as one typically does (amiright? right?) and found a real gem of a letter. A French physician wrote of a special patient that had recently visited his practice, an 83-year old Parisian gentleman complaining of fatigue and weight loss. Upon clinical examination, he discovered the man had hyper-eosinophilia (high numbers of granulocytes, a type of white blood cells) indicating that something might be a bit off - either an allergic reaction or some sort of infection (1). A series of tests were run, including a stool sample, but nothing definitive was detected.
The parasite Strongyloides stercoralis, otherwise known as threadworm due to its filiform shape. What a cutie pie! Image: eHow. Click for source.
Until the man spoke of a trip to Vietnam many years ago. Something on the order of 75 - yes! seventy-five! - years ago. The physician realized that the patient may have something out of the ordinary and, quite possibly non-Frenchy, on his hands. Serologic testing then identified evidence of Strongyloides stercoralis infection and the larvae were subsequently found in a new stool sample. This man had been unknowingly harboring a S. stercoralis, or threadworm, infection for over 75 years.
The longest period of threadworm auto-infection that I had heard of ranged from 30-40 years. But reading that a man had a 75-year old infection made my jaw drop. I immediately set out to find more about chronic, long-term threadworm infections and found that this infection plays an important role when considering the repatriation of former prisoners of war (FPOWs), especially those that have served in the tropics.
Strongyoides stercoralis is a type of roundworm known as "threadworm" for its delicate, filiform shape. Just as we’ve encountered with hookworm, it is soil-transmitted so now you have one more reason to wear shoes while weeding your rice paddies. It is endemic in tropical and subtropical climes, and is particularly common in west Africa, the Caribbean and southeast Asia.
The threadworm larva takes a rather circuitous trip after penetrating the soles of your naked feet, embarking upon a veritable survey of the human body - migrating through the circulation system to the lungs, crawling up the respiratory tract to be swallowed and ultimately delivered to their new home in the small intestine.
The real trouble with threadworm begins when the adults start to reproduce (doesn’t it always?). Eggs are deposited in the lumen and larva hatch in the intestine to be excreted in the feces and begin the cycle anew. But oftentimes the offspring can result in endogenous auto-infection, in other words, the parasitic circle of life in your belly and body, seemingly ad infinitum. This chronic infection can be fairly well tolerated, being typically asymptomatic, though mild gastrointestinal symptoms and a furiously itchy rash known as "larva currens" have been reported. The linear-looking rash is caused by migrating larva and physicians have noted that they can often follow the tracks of the quickly-moving larva, hence the name. Really, there's nothing like knowing you're parasitized till you see the buggers’ route under your skin.
The characteristic "larva currens" rash, showing the larva's trajectory under the skin. The rash is excruciatingly itchy. Image: 2011 DermIs. Click for source.
A quite serious complication of endogenous infection can arise for the severely immunocompromised - an overwhelming, fulminant infection in which larva permeate multiple organs, known as "widespread dissemination". The larva may be found in the liver, lungs and central nervous system, bringing about bacterial meningitis and septicemia. This potential complication has earned the parasite the distinction of being the leading cause of death from a parasitic infection in the United States (2).
Now. As mentioned, S. stercoralis is endemic in many tropical, warm climates and, for the most part, is only found in those regions infecting the local population. There are, however, some unique circumstances when visitors such as our Parisian gentleman visit distant shores for touristic, business or, regrettably, militaristic purposes, and find themselves bringing home an unexpected souvenir.
The subject of unannounced visitors brings us to the Allied campaign in Singapore. In February 1942, the city of Singapore was lost to the Japanese army during the Malaya campaign of World War II. The Fall of Singapore is considered to be one of the greatest British military disasters, with over 100,000 Allied troops consisting of British, Australian, American and Dutch soldiers captured. Winston Churchill deemed it the “greatest disaster and capitulation” in British history (8). In September of the same year, tens of thousand prisoners were delivered to Thailand in cattle trucks as slave labors to work on the construction of the Burma Railway, intended as a supply line to strengthen Japan’s invasion into Burma. The POWs were ultimately joined by roughly 250,000 Javanese, Malay, Burmese, Chinese and Indian laborers recruited by the Japanese (6).
Former POWs in an unknown prisoner camp near the Burma Railway. Image: Unknown. Click for source.
Construction of the railway was incredibly taxing, torturous work over rugged, mountainous and jungly terrain in stifling humid weather. No machinery was used - the entire railway was built by hand, hammer and hoe (6). Prisoners were rarely fed and malnutrition was rampant. Many were shoeless. Regular beatings by their Japanese captors were common. Infectious diseases ravaged men unaccustomed to the tropical climate - malaria, dysentery and cholera were ubiquitous among the prisoners. Many limbs were amputated as a result of tropical ulcers and accidents, rarely aided by medical instruments and medicine. Many men perished from starvation, beatings and disease. It is conservatively estimated that over 16,000 POWs and 80,000 southeast Asians died during its construction earning the Burma Railway the notorious moniker "The Death Railway".
Several medical surveys of these former prisoners of war (FPOWs) condemned to work on the railway have been completed and many communicable illnesses were identified but the most frequently encountered long-term ailment has been threadworm (5). A good example is a survey conducted amongst 160 Australian serviceman of the 2/4 machine-gun battalion that had been captured in Singapore in January of 1942 (4). Direct microscopy of their feces as well as identification of the presence of threadworm larva indicated that 44 of the men (27.5%) were infected nearly 38 years after the primary infection. They showed high rates of elevated eosinophilia as well as serum IgE concentrations, further corroborating threadworm infection. The men were also significantly thinner and more likely to show gastrointestinal symptoms compared to their non-infected peers.
The Burma Railway, cutting through mountains, jungle and rivers, as seen today. Image: Unknown. Click for source.
Many more FPOWs may currently be or have been infected but considering that the median age for American WII veterans is now 88 years old, I can imagine they have greater health-related issues to worry about then a few parasitic roommates (6). Threadworm has also been identified in American FPOWs that had served in the Vietnam War, though they show significantly lower rates of infection compared to their older counterparts. Most studies have indicated that 15 to 20% of WWII FPOWs that had worked on the Burma Railway were infected with Strongyloides, whereas Vietnam FPOWs were infected at a rate of less than 5% (7)(9); I imagine that the forced labor aspect of the WWII soldiers imprisonment has something to do with this vast difference in infection rates.
Parasitic loads can be low and larva may appear infrequently in feces, making detection of Strongyloides rather difficult through common parasitological methods. As one paper suggested, "large and repeated quantities of feces often need to be examined" (3). I imagine it's quite difficult to convince a patient to consistently yield to this sort of request by researchers. An alternative method that has shown great efficiency is the use of the string test to sample the duodenum. ELISA tests to detect antibodies to the parasite are also quite successful.
The most remarkable aspect of this parasite is its ability to survive autonomously for the lifetime of its host, replicating until the proverbial cows come home, distinguishing it from other parasites. Several researchers have noted the importance of physicians being aware of returning travelers, expatriates and service members with a history of travel in endemic areas, the characteristic larva currens rash and evidence of eosinophilia (9). And, of course, immigrants and refugees from these regions ought to be screened. These FPOWs lost more than their liberty during their imprisonment and torture - they also lost their long-term health to these creepy-crawlies. The plight of these men and their suffering should serve as a reminder to complete thorough medical screening of all military veterans. And to always, always wear shoes in the tropics. Sayonara!
I breezed through the life cycle of Strongyloides stercoralis and really haven't given it justice. For more information on its life cycle, symptoms, treatment and much more, visit the CDC's great diagnostic page here.
There is a staggering amount of information and links on this website regarding FPOWs, life in the prisoner camps and general info for WWII history fanatics.
For more detail on the Burma Railway and FPOW, this is a nice resource with personal accounts.
References (1) Prendki V, Fenaux P, Durand R, Thellier M, Bouchaud O. (2011) Strongyloidiasis in man 75 years after initial exposure. Emerg Infect Dis. 17(5): 931-2. (2) MuennigP, PallinD, SellRL,et al. (1999) The cost effectiveness of strategies for the treatment of intestinal parasites in immigrants. N Engl J Med.340:773 – 779. (3) Grove DI. (1980) Strongyloidiasis in Allied ex-prisoners of war in south-east Asia. Br Med J.280(6214): 598–601. Gill GV, Welch E, Bailey JW, BEll DR and Beeching NJ. (2004) Chronic Strongyloides stercoralis infection in former British Far East prisoners of war. Q J Med97:789–795 (5) Gill Vand DR Bell. (1980) Letter: Strongyloidiasis in ex-prisoners of war in south-east Asia. British Med J.280(6227): 1319. (6) United States Department of Veterans Affairs. "FY07 Annual VA Information Pamphlet (February 2008)". Retrieved 08-2011 (7) Genta RM, Weesner R, Douce RW, Huitger-O'Connor T, Walzer PD. (1987) Strongyloidiasis in US veterans of the Vietnam and other wars. JAMA, 258(1):49-52 (8) Graeme P. (2007) ‘Living in Hell but Still Smiling': Australian Psychiatric Casualties of War during the Malaya- Singapore Campaign, 1941-42. Health and History. 9(1):28-55 (9) Pelletier LL Jr, Gabre-Kidan T. (1985) Chronic Strongyloidiasis in Vietnam veterans. Am J Med.78(1):139-40.
Prendki V, Fenaux P, Durand R, Thellier M, & Bouchaud O (2011). Strongyloidiasis in man 75 years after initial exposure. Emerging infectious diseases, 17 (5), 931-2 PMID: 21529417