Tungiasis is an inflammatory skin disease caused by infection with the female ectoparasitic Tunga penetrans, a flea also known as the chigoe, chigo, chigoe flea, chigo flea, jigger, nigua, sand flea, or burrowing flea (and not to be confused with the chigger, a different arthropod). The flea and the disease that it causes are found in the tropical parts of Africa, the Caribbean, Central and South America, and India. Tunga penetrans is the smallest known flea, measuring 1 mm across. It is also known in Latin America as the nigua and bicho de pie (Spanish) or bicho de pé (Portuguese), literally "foot bug". Tunga penetrans is a member of the genus Tunga, which comprises 13 species.
Tungiasis causes skin inflammation, severe pain, itching, and a lesion at the site of infection that is characterized by a black dot at the center of a swollen red lesion, surrounded by what looks like a white halo. Desquamation of the skin is always seen, especially after the flea expands during hypertrophy.
As of 2009, tungiasis is present worldwide in 88 countries with varying degrees of incidence. This disease is of special public health concern in highly endemic areas such as Nigeria, Trinidad and Tobago, and Brazil, where its prevalence, especially in poor communities, has been known to approach 50%.
The chigoe flea is properly classified as a member of the order Siphonaptera as it is a flea. Although commonly referred to as chiggers, true chiggers are mites, which are minute arachnids. Mites penetrate the skin and feed on skin cells that are broken down by an enzyme they secrete from their mouthparts, but they do not lay eggs in the host as T. penetrans does. Moreover, in mites, the adult and the larval forms both feed on other animals. This is not the case with T. penetrans, as only the adults feed on mammals and it is only the female that stays attached to the host.
Tunga penetrans is also known by the following names: chigoe flea, sand flea, nigua, chigger flea, jigger flea, bicho de pé, pico, sikka, kuti, and piqui, among many others.
Another species of Tunga, T. trimamillata causes tungiasis in Ecuador and Peru.
Signs and symptoms
thumb|Tunga penetrans in human skin
thumb|Typical Tunga penetrans presentation under human toes
The symptoms of this disease include:
- Severe pruritus
- Pain
- Inflammation and swelling
- Lesions and ulcerations, with black dots in the center
If a Tunga infection is left untreated, secondary infections, such as bacteremia, tetanus, necrosis and gangrene, may be expected.
In all cases, tungiasis by itself only caused morbidity, though secondary infection may lead to mortality. The life cycle section presents the Fortaleza stages from the flea's developmental perspective. The discussion is specific to symptoms of human infection. The clinical presentation in humans follows the Fortaleza Classification as the stage of infection will determine the symptoms present. The following discussion will give an overview of the symptoms beginning in stage 2 because patients are not likely to present themselves at the early stages of infection, mostly because the flea's burrowing is usually not felt. This may be due to a keratolytic enzyme secreted during stage 1.
Incubation
Because of the relatively rapid onset of tungiasis, the incubation period tends to be short. Although some reddening around the site of penetration occurs, the first symptoms are perceived in stage 2 as itching and severe pain, usually a day after penetration.
Cause
Tungiasis is caused by chigoe fleas (the term transmission does not apply because Tunga penetrans is itself responsible for the disease.) The preponderance of tungiasis lesions on the toes may be because chigoe flea is a poor jumper, attaining only a height of 20 cm. But the reality is more complex; for example, the jumping ability cannot explain why hands are the second-most affected body part. Lesions on the hands are better explained by playing in the sand and noting that hands are often used to remove sand from other parts of the body. The occurrence of tungiasis lesions on the toes, between them, and on the soles can be easily explained because most of the victims are poor, walk barefoot, and live in places where the sand (home to chigoe fleas) constitutes the floor. Rate of incidence therefore is greatly increased in poor communities and populations because of the lack of adequate housing. This occurs in significantly higher proportions during the peak of the dry season in local communities.
Tungiasis in humans and some domestic animals can also be caused by Tunga trimamillata, which is known to exist in Ecuador and Peru.
Reservoirs and transmission
T. penetrans has been documented to use various warm-blooded animals as reservoir hosts, including humans, pigs, dogs, cats, rats, sheep, cattle, donkeys, monkeys, birds, and elephants.
The chigoe flea eggs' average length is 604 μm and the just hatched larvae, in their first instar, have an average length of 1,500 μm. At the second and last instar (T. penetrans is unique among the fleas in that it only has two, instead of three, instars.) the larvae decrease in size to 1,150 μm after growing to at least 2,900 μm. The development from instar 1 to instar 2 lasts less than one day.
The use of pesticide, like DDT, has also led to elimination of the Tunga penetrans, but this control/prevention strategy should be utilized very carefully, if at all, because of the possible side effects such pesticides can have on the greater biosphere. In the 1950s, there was a worldwide effort to eradicate malaria. As part of that effort, Mexico launched the Campaña Nacional para la Erradicación de Paludismo, or the National Campaign for the Eradication of Malaria. By spraying DDT in homes, the Anopheles a genus of mosquitoes known to carry the deadly Plasmodium falciparum was mostly eliminated. As a consequence of this national campaign, other arthropods were either eliminated or significantly reduced in number, including the reduviid bug responsible for Chagas disease (American Trypanosomiasis) and T. penetrans. Controlled, in-home spraying of DDT is effective as it gives the home immunity against arthropods while not contaminating the local water supplies and doing as much ecological damage as was once the case when DDT was first introduced.
While other species gradually gained resistance to DDT and other insecticides that were used, T. penetrans did not; as a result, the incidence of tungiasis in Mexico is very low when compared to the rest of Latin America, especially Brazil, where rates in poor areas have been known to be as high or higher than 50%. There was a 40-year period with no tungiasis cases in Mexico. It was not until August 1989 that three Mexican patients presented with the disease. Though there were other cases of tungiasis reported thereafter, all were acquired in Africa.
Treatment
thumb|Removed parasite
As the disease is self-limiting, at least when exposure to the parasite is limited, management is mostly confined to treatment. Due to the secondary infection that can cause serious medical issues, the recommended course of action upon diagnosis is a surgical extraction of the fleas followed by the application of a topical antibiotic. Care should be taken to avoid tearing the flea during the extraction procedures as severe inflammation will result. The same will occur if part of the flea is left behind. Sterile equipment should always be used, as contaminated instruments could act as mechanical vectors for pathogens to enter the body.
Topical treatment with low-viscosity dimethicone silicone oils, commonly used for head lice, is an emerging and effective method for suffocating parasites without the use of toxins. The World Health Organization has recognized this treatment as both highly effective and safe, based on extensive research and its application in severe cases of parasitic infestations. These low-cost oils have demonstrated a strong track record in the global treatment of even treatment-resistant head lice, making them a promising option for addressing this neglected tropical disease.
Even without treatment, the burrowed fleas will die within five weeks and are naturally sloughed off as the skin sheds.
Epidemiology
For the most part, the chigoe flea lives 2–5 cm below the sand, an observation which helps explains its overall distribution. The temperature is generally too hot for the larvae to develop on the surface of the sand and the deeper sand does not have enough oxygen. This preferred ecological niche offers a way to decrease transmission among humans by investing in concrete grounds as opposed to the sand that is usually used in shacks and some favelas. Indeed, Nany et al. (2007) report that "In shacks with concreted ground being cleaned every day with water, Tunga [penetrans] larvae were hardly found." The first case of tungiasis was described in 1526 by Gonzalo Fernández de Oviedo y Valdés, where he discussed the skin infection and its symptoms on crew members from Columbus's Santa Maria after they were shipwrecked on Haiti. Through ship routes and further expeditions, the chigoe flea was spread to the rest of the world, particularly to the rest of Latin America and Africa. The spread to greater Africa occurred throughout the 17th and 19th centuries, specifically in 1872 when the infected crewmen of the ship Thomas Mitchell introduced it into Angola by illegal dumping of sand ballast, having sailed from Brazil.