Tungiasis

Tungiasis is a cutaneous parasitic infection caused by the female sand flea Tunga penetrans, which embeds into the skin, most commonly in the feet, leading to a localized inflammatory response. It is considered a neglected tropical disease, primarily affecting impoverished populations in endemic regions and receiving limited attention in public health initiatives despite its significant morbidity.

The gravid female flea, approximately 1 mm in size, penetrates the skin, most often in areas that come into direct contact with the ground, such as the periungual and interdigital regions of the feet. The primary site of transmission is the unsealed floor of sleeping areas, where off-host stages of the flea develop. Once embedded, the flea burrows into the epidermis with only the posterior tip of its abdomen exposed, which allows for respiration, excretion, and egg-laying. Within the skin, the flea feeds on blood and undergoes marked hypertrophy, increasing nearly 2000-fold in size as it matures and its eggs develop. Over the course of about 7 days, it forms a painful, raised, circular lesion approximately 1 cm in diameter. A free-living male copulates with the embedded female during this period. The female releases hundreds of eggs through her exposed abdominal tip, which fall to the ground and hatch into larvae, continuing the off-host stages of the life cycle. The presence of the flea induces local tissue disruption, inflammation, and often secondary bacterial infection. After approximately two weeks, the flea dies in situ and is either expelled or gradually absorbed by the surrounding tissue.

Tungiasis is endemic in resource-limited tropical and subtropical regions of sub-Saharan Africa, South America, and the Caribbean. It primarily affects children and the elderly in impoverished communities with limited access to footwear and adequate sanitation. Prevalence varies widely by region and setting. In Kenya, the national prevalence is approximately 1.4% among children aged 8-14 years, but school-level estimates range from less than 1% to 22% depending on location. In remote rural areas, the burden is substantially higher. In southwestern Ethiopia in 2016, the prevalence among children aged 5-14 years exceeded 50%. Similarly, in northeastern Uganda in 2021, 62.8% of adults and children were affected.

Walking barefoot in endemic regions, living in sandy or dusty environments, and exposure to poor housing conditions and sanitation increase the risk of tungiasis. Infestation is particularly common in communities where sleeping quarters have unsealed earthen floors, bathing is infrequent, and soap is seldom used. Close proximity to infested animals (especially pigs and dogs) further contributes to transmission, and limited access to medical care exacerbates the burden in affected populations.

Initial symptoms of tungiasis include localized pain, itching, and erythema at the site of penetration, usually on the feet or hands. Toes, soles, and heels are the most frequently affected areas. Within days, a characteristic nodular lesion develops, typically presenting with a central black dot corresponding to the posterior end of the embedded flea. The lesion may be surrounded by desquamation and is frequently complicated by secondary bacterial infection. As the flea enlarges and matures within the skin, inflammation intensifies, often accompanied by increased tenderness and functional impairment. In cases of multiple lesions, particularly on weight-bearing areas of the foot, ambulation can become painful or impaired. The infestation commonly leads to secondary bacterial infections, with abscess formation and suppuration. Bacterial superinfection may progress to cellulitis, lymphangitis, chronic lymphedema, and, in severe cases, life-threatening complications such as sepsis, tetanus, and post-streptococcal glomerulonephritis. Spontaneous involution occurs over several weeks if the flea is not removed, but persistent or recurrent infestation is common in endemic settings. The severity of tungiasis is often defined by the number of viable embedded fleas, though thresholds may vary. Some classifications consider 1-5 fleas as mild and > 5 as severe, while others use 1-10 and > 10, respectively. The choice of threshold may depend on factors such as patient age (especially in children where minimizing procedural pain is a priority), location of lesions, the clinical setting's sanitation, the number of individuals needing treatment simultaneously, and local sociocultural norms regarding healthcare access and parasite recognition.

With appropriate management, including lesion extraction, wound care, and control of secondary infection, tungiasis typically resolves without long-term sequelae. If left untreated, tungiasis can result in significant morbidity, including nail deformation or loss, disfigurement of the feet, ulceration with extensive tissue necrosis, and difficulty walking. In advanced cases, chronic inflammation may lead to auto-amputation of digits and immobilization. Repeated infestations can lead to significant morbidity, particularly in vulnerable populations.