Discussion

Enterobius vermicularis is a common human intestinal parasite which causes infections predominantly in young children (5–10 years). Classical pinworm infections present with pruritis ani and perineal pruritis caused by mechanical irritation and allergic reaction, which often manifest in children as irritability, insomnia and enuresis. Although the classical symptom of pruritis ani was characteristically absent in our case, the patient complained of disturbed sleep due to vulval itching. Whereas previous researchers have reported E. vermicularis as a common infection in young girls with severe pruritis associated with a thin, colourless vaginal discharge (Makwela, Reference Makwela2007), there was no history of any genital complaints other than vulval itching in the present case. The ascent of larvae from the perineum into the female genital tract has been documented on a few occasions (Athanasios et al., Reference Athanasios, Maria and Polyanthi2007). However, the absence of gastrointestinal symptoms together with negative stool findings, and multiple recurrences despite complete treatment, are causes of concern in the present case. Normally, gravid female worms, after their nocturnal migration to the anal region, deposit up to 10,000 eggs which embryonate within hours and remain viable for up to 20 days. In the present case eggs were neither present in any vaginal nor anal swabs, nor in stool samples. On the contrary, 5–6 live worms could be demonstrated on all occasions from vaginal swabs.

Enterobius vermicularis, being a lumen dweller, mainly causes infections that are asymptomatic. Occasionally adult pinworms migrate to an ectopic site and, although this is rare, female worms deposit eggs, usually at night (Symmers, Reference Symmers1950). This causes discomfort and itching around the perineum and also results in urethritis and vaginitis. Worms may invade the abdominal cavity via the uterus and uterine tube, causing salpingitis and granulomata in various abdominal organs (Das et al., Reference Das, Pathan, Hira, Madda, Hasaniah and Juma2001).

Enterobiasis remains a common problem today and infection rates can reach epidemic proportions in institutions such as schools, camps, dormitories, etc. Four methods of transmission exist (Cook, Reference Cook1994): (1) direct infection from the anal and perianal regions by fingernail contamination or autoinfection and soiled night clothes; (2) exposure to viable eggs on soiled bed linen and other contaminated environmental objects; (3) exposure to contaminated dust containing embryonated eggs usually from clothes, linen, toys, furniture and animal fur; and (4) retro-infection where larvae migrate into the sigmoid colon and caecum after hatching on the anal mucosa. Family members and sexual contacts require therapy simultaneously to prevent re-infection and spread of the disease, as an asymptomatic infection in another family member, often a small child, can serve as a reservoir of infection. Careful hand-washing and environmental decontamination are also important in reducing transmission.

Another feature of this infection is the inevitable diagnostic challenge encountered in such cases. An examination of stool samples demonstrates eggs in only 5–15% of cases because female worms do not lay eggs in stools but on the perianal skin. Using a Sellotape test, diagnosis is best carried out each morning for several successive days prior to washing or defecation. For example, 50% of children can show positive samples on the first morning, which increases up to 99% after five successive morning samples; whereas six consecutive negative results on a daily basis would indicate a lack of infection (Caldwell, Reference Caldwell1982; Cook, Reference Cook1994).

Adult worms of E. vermicularis have a short life cycle of only 3–6 weeks, which makes it possible to break the- cycle of infection by impeccable hygiene. However, this- approach seems impractical due to the high adaptability of E. vermicularis to its host and the lack of effective anthelmintic therapy. Cure rates of 90–100% are reported with mebendazole. Re-infection occurs primarily as a result of the ongoing transmission of eggs or larvae. Albendazole is better tolerated and more effective than mebendazole and may be preferable for an ectopic infection due to the poor systemic absorption of mebendazole. Experience with mebendazole treatment for extra-intestinal enterobiasis is limited, which was quite evident in our case where the patient had recurrent episodes despite complete treatment with mebendazole. Moreover, there is a paucity of information on alternative local treatment options available for vaginal enterobiasis, especially in a paediatric patient. Control of enterobiasis is difficult because of the pinworm's short life cycle, leading to frequent recurrences. Therefore retreatment of the entire family for 2 weeks is advisable since the drugs kill adult worms not eggs.

However, in the present case, despite complete anthelmintic treatment and resulting negative stool and urine samples, the occurrence of living worms in the vaginal fornix on multiple occasions suggested that the focus of infection was the vagina. Chronic Enterobius genitourinary infections with pyuria and demonstrable eggs and larva in urine and vaginal discharge have been recorded in India and treated with piperazine (Singh & Samantaray, Reference Singh and Samantaray1989). The case presented here is unusual because live adult pinworms were recovered from the anterior fornix of the vagina on multiple occasions despite complete treatment, but were not associated with pruritis ani. Recurrent vaginal enterobiasis despite treatment and in the absence of any gastrointestinal or genitourinary complaints suggests that the vagina is a potential reservoir for E. vermicularis. This supports the theory that rare ectopic enterobiasis could ascend through the female genital tract. The case highlights the presence of live E. vermicularis in the vagina causing vulval itching and discomfort, thereby emphasizing the importance of a thorough examination, regular health education and the importance of personal hygiene. This case also highlights the need to develop anthelmintic preparations that can be used in suspected vaginal infections of E. vermicularis, especially in paediatric patients.