Fausto Bustos

Parasites and Pestilence, Winter 2009

Parasite Report on Tungiasis and Tunga penetrans

Stanford University

 

Parasite

 

My parasite is Tunga penetrans which causes the disease tungiasis.

 

Introduction

 

SEM of an adult male T. penetrans flea feeding on a rat’s foot.

From Medical and Veterinary Entomology Vol. 18, 4 Pages: 439-441

© The Royal Entomological Society, 2004 [18]

 

Tungiasis is a neglected inflammatory skin disease caused by infection of the female ectoparasitic Tunga penetrans flea that is found in sub-Saharan Africa, the West Indies, Central and South America, Pakistan, and India. [1,2] Tunga penetrans is the smallest flea in the world, measuring 1mm across, and is commonly referred to as the chigeo, sand, jigger flea, or chigger flea in the English-speaking world. It is also known in Latin America as the nigua and bicho de pie.

 

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.

 

Although this disease is self-limiting in that the female flea that causes the disease dies after releasing eggs, tungiasis can cause misery if several lesions are present. Pus is often present in such cases and often accompanies tissue and nail deformation. Secondary infection is also possible. [3]

 

As of 2009, tungiasis is present worldwide in 88 countries with varying degrees of incidence. [4] This disease is of special public health concern in highly endemic areas like Nigeria, Trinidad, Tobago, and Brazil where its prevalence, especially in poor communities, has been known to approach 50%. [5]

 

Synonyms

 

Tunga penetrans is also known by the following names: chigoe flea, sand flea, nigua, chigger flea, jigger flea, bicho de pie, pico, sikka, kuti, and piqui, among many others. It is also known as Sarcopsylla penetrans and Pulex penetrans. [3] In this report, the binomial nomenclature and the term chigoe flea will be used.

 

Classification and Taxonomy

 

The chigoe flea is properly classified as a member of the Pulicidae family as it is a flea. Although commonly referred to as chiggers, those are mites who are minute arachnids. [6] Mites penetrate the skin to drink blood but they do not lay eggs 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 belongs to the kingdom Animalia, the phylum Arthropoda, the class Insecta, the order Siphonaptera, the family Pulicidae, the genus Tunga, and the species penetrans. [7] The scientific name is Tunga penetrans Linnaeus, 1758.

 

History of Discovery

 

From the existing literature, it seems T. penetrans is native to the West Indies. 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. [8] 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 1873 when the infected crewmen of the ship Thomas Mitchell introduced it into Angola having sailed from Brazil. [9-10]

 

Reservoir

 

Strictly defining reservoirs as organisms that convey a disease without being susceptible to it themselves, tungiasis has no reservoirs as the female will cause the inflammatory skin disease after it borrows in any mammal. A more flexible definition of what a reservoir is would allow the hosts to be seen as reservoirs, but the standard parasitological definition of a reservoir would then be lost. Tungiasis, then, has as high a number of vectors as it does hosts.

 

Vectors

 

Due to the fact that the gravid female will expel at least 100 to at most 200 eggs, hosts are the vectors themselves because they can easily spread the eggs to other mammals, though usually indirectly. T. penetrans has been documented to cause tungiasis in humans, pigs, dogs, cats, rats, sheep, cattle, donkeys, monkeys, elephants, and other mammals. [1,4] Tungiasis has not been reported in reptiles and birds, although it is probable that birds could more easily acquire the disease due to its lack of scales. In any event, reptiles and bird would be accidental hosts at the least and possibly dead-end hosts at best. Lacking firm evidence, it remains to be seen whether T. penetrans could go through all stages of the Fortaleza Classification, the stages of T. penetrans infection, in non-mammalian species described in later sections.

 

Transmission

 

Transmission of tungiasis is strictly by infection of Tunga penetrans. The flea is able to jump only 20 cm, which explains why tungiasis lesions are most commonly found on the periungal region of the toes. Rate of incidence, and transmission via the ejected eggs among people, is greatly increased in poor communities and populations because of the lack of adequate housing. [11] This occurs in significantly higher proportions during the peak of the dry season in local communities, as discussed below. [12]

 

Epidemiology

 

A map showing the worldwide distribution of Tungiasis as of 2009. Taken from GIDEON. [13]

 

For the most part, the chigoe flea lives 2-5cm below sand, an observation which helps explains its overall distribution. The temperature is generally too hot for the larvae to develop and the deeper sand does not have enough oxygen. [1] 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 larvae were hardly found.” [1]

 

Image from American Journal of Tropical Medicine and Hygiene, Heukelbach et al. 72 (2): 145. 2005. [12]

 

In a longitudinal study conducted from March 2001 to January 2002, incidence of tungiasis was found to vary significantly with the local seasons of an endemic community in Brazil. In particular, the study found that “occurrence of tungiasis varies throughout the year and seems to follow local precipitation patterns. Maximum and minimum prevalence rates differed by more than a factor of three.” The authors suggest that the correlation is due to the high humidity in the soil impairing larval development during the rainy season, as well as the more obvious reason that rain may simply wash away all stages of T. penetrans due its small size of 1mm. [12]

 

Acting as both biological vectors and definitive hosts, humans have spread Tunga penetrans from its isolated existence in the West Indies to all of Latin America and most of Africa via sea travel. Since the chigoe flea technically has no reservoir species and the female will cause tungiasis to any mammalian organism it can penetrate, this means the flea will have a relatively large amount of hosts and victims. Epidemiologically, this is important as tungiasis often causes secondary infections as well that are described in more detail later on. [1,2,4]

 

The modern ease and availability of transportation and travel has enhanced the possibility for greater worldwide incidence and made tungiasis a public health concern in regions where it is not normally present, such as in the United States where the first case was reported in 1930 by Faust and Maxwell. [14] With increased incidence due to travel to Latin America and Africa, then, a patient’s history must be taken into account for diagnosis.

 

Incubation Period

 

Because of the relatively rapid onset of tungiasis, the incubation period tends to be short. Although there is some reddening around the site of penetration, the first symptoms are perceived in stage 2 as itching and severe pain, usually a day after penetration. [11]

 

Life Cycle

 

The life cycle diagram is provided as an addendum to this report due to its size. Including it here would diminish the amount of detail and information that could be gleaned from it. As far as I have been able to ascertain, this is the only life cycle diagram that exists. I have been emailing professors who wrote many of the articles I read for this report, and they only had representations of the life cycle diagram, like the Fortaleza Classification image below, to give me. The life cycle diagram was compiled using images from several articles I read and contains the main information about the life cycle of the chigoe flea; it also describes the stages of the Fortaleza Classification, thereby including the clinical stages of tungiasis.

 

Fortaleza Classification

 

Provided by Hermann Feldmeier via email correspondence. [15]

 

In a seminal paper on the biology and pathology of Tunga penetrans, Eisele et al (2003) provided and detailed the five stages of tungiasis. In dividing the natural history of the disease, the Fortalez Classification (though it seems more appropriate to call it the Fortaleza Cycle) formally describes the last part of the female flea’s life cycle where it burrows into its host’s skin, expels eggs, and dies. The diagram shown above comes from one of the authors of the paper, Professor Hermann Feldmeier, a WHO expert in the control of parasitic diseases. I have adapted and translated the diagram from the original German for ease of discussion. This section surveys the Fortaleza stages from the flea’s perspective; the flea, not the symptoms, will take precedence here. The clinical symptoms are presented in the next section. However, due to the nature of the discussion, overlap with other sections, particularly the one on symptoms, is unavoidable.

 

Stage 1 is characterized by the penetration of the skin by the female chigoe flea. Running along the body, the female uses its posterior legs to push its body upward by an angle between 45-90 degrees. Penetration then starts, beginning with the proboscis going through the epidermis. [11]

 

By stage 2 (day 1-2), penetration is complete and the flea has burrowed most of its body into the skin. Only the anus, the copulatory organs, and four rear air holes in fleas called stigmatas remain on the outside of the epidermis. The anus will excrete feces that is thought to attract male fleas for mating, described in a later section. The hypertrophic zone between tergites 2 and 3 in the abdominal region begins to expand a day or two after penetration and takes the appearance of a life belt. During this time, the flea begins to feed on the host’s blood. [11]

 

The hypertrophic section of the female begins to expand in stage 2.

Image provided by Heinz Mehlhorn, editor of the Encyclopedia of Parasitology, 3rd Edition. © Springer-Verlag 2008. [17]

 

Stage 3 is divided into two morphologically and clinically different substages, the first of which being 2-3 days after penetration is complete. In 3a, maximum hypertrophy is achieved and the flea’s midsection swells to the size of a pea. Due to the expanding flea, the outer layer of the skin is stretched thin, resulting in the appearance of a white halo around the black dot (rear end of the flea) at the center of the lesion. In 3b, the chitin exoskeleton of tergites 2 and 3 increase in thickness and gives the structure the look of a mini caldera. Egg release is common in substage 3b, as are fecal coils. The eggs tend to stick to the skin, possibly through adhesive proteins. [11]

 

At about the 3rd week after penetration, stage 4 begins, which is also divided into two substages. In 4a, the flea loses its signs of vitality and appears near death. As a result, the lesion shrinks in size, turns brown, and appears wrinkled. The death of the flea marks the beginning of substage 4b (around day 25 post-penetration) as the body begins to eliminate the parasite through skin repair mechanisms (e.g. shedding and subsequent skin repair). At this phase, the lesion is seen as brown or black. [11]

 

By the 5th stage of tungiasis, the carcass of the T. penetrans flea has been expelled and there are residues of the infection that remain. As there are only residual symptoms at this stage, the details have been omitted here but can be found in the proceeding discussion.

 

Clinical Presentation in Humans

 

During stage 3, fecal coils and an increase in both the size of the lesion and number of tungiasis symptoms increase. Here, skin desquamation is clearly visible.

Taken from Eisele et al. © Springer-Verlag 2003. [11]

 

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. It should be noted that the discussion is specific to symptoms of human infection. The dates for stages and symptoms may be different for different animals due to anatomical variations. See Nagy et al (2007) for a discussion of tungiasis development in rats.

 

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. [1,2]

 

The patient with a single flea may present as early as stage 2 when, though the erythema is barely perceptible, a boring pain and the curious sensation of pleasant itching occur. This inflammatory reaction is the initial immunological response to the infestation. Heavily infested patients may not notice a stage 2 infection due to the other fleas’ causing irritation as well. Feces may be seen, but this is more common in the 3rd stage. [11]

 

Shiny yellow white eggs being released by the female chigoe flea. Sometimes the eggs will land farther away from lesion than is shown here.

Image taken from www.healthinplainenglish.com [16]

 

Around the third day after penetration, erythema and skin tenderness are felt, accompanied by pruritus (severe itching) and a black furuncular nodule surrounded by a white halo of stretched skin caused by the expansion of the flea. Fecal coils may protrude from the center of the nodule where the flea’s anus is facing upward. They should be washed off quickly as the feces may remain in the skin unless removed. During this 3a substage, pain can be severe, especially at night or, if the nodule is on the foot, while walking. Eggs will also begin to be released and a watery secretion can be observed. The radical metamorphosis during the 3rd to 6th day after penetration, or neosomy, precedes the formation of a small caldera-like rim rampart as a result of the increased thickness of the flea’s chitin exoskeleton. During the caldera formation, the nodule shrinks a bit and it looks as if it is beginning to dry out; this takes 2 weeks and comprises substage 3b. [11]

 

At the 3rd week after penetration and substage 4a, the eggs’ release will have stopped and the lesion will become smaller and more wrinkled. As the flea is near death, fecal and water secretion will stop altogether. Pain, tenderness, and skin inflammation will still be present. Around the 25th day after penetration, the lesion looks like a black crust and the flea’s carcass is removed by host repair mechanisms and the skin begins to heal. With the flea gone, inflammation may still persist for a while. [11]

 

Although patients would not present with in the 5th stage of tungiasis as the flea would be dead and no longer in the body, this stage is characterized by the reorganization of the skin (1-4 weeks) and a circular residue of 5-10mm in diameter around the site in penetration. An intraepithelial abscess, which developed due to the presence of the flea, will drain and later heal. [17] Although these disease residues would persist for a few months, tungiasis is, for all intents and purposes, no longer present. [11]

 

Severe tungiasis present on the foot. Tissue deformation is clear.

Taken from Heukelbach. “Tungiasis.” [3]

 

In severe cases, ulcers are common, as well as complete tissue and nail deformation. A patient may unable to walk to due severe pain if too many of the lesions are present in the feet. Suppuration (pus formation), auto-amputation of digits (via ainhum), and chronic lymphedema may also be seen. [2] If the patient is not vaccinated, tetanus if often a complication due to secondary infection. Gangrene is another common complication of severe infestation and superinfection. Staphylococcus aureus and Wolbachia endobacteria can be transmitted by the chigoe flea, as well as nearly 150 other different pathogens. For these reasons, the chigoe flea should be removed as soon as possible. [3, 18, 19]

 

Reproduction & Fitness

 

Females have a depression or groove at their abdominal end whereas the males have their protrudable copulatory organs in that same region. These morphological differences reflect the way the male and female copulate. In the first step toward copulation, the female penetrates an organism in an ungravid state. It is only there that the male will find her and copulate. Copulation of adults has not been observed in the wild. With the female reproductive organs pointing outward, the male will place his reproductive organs “in direction to the upright abdominal end of the female” to copulate. [1] Having copulated for only a few seconds to 2 minutes, the male will then take search for another female. After copulation is complete, the male will die, although sometimes he will take a blood meal before doing so. Interestingly, eggs will be expelled whether or not they have been fertilized. [20]

 

The chigoe flea eggs’ average length is 604 mm and the just hatched larvae, in their first instar, have an average length of 1,500 mm. 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 decreases in size to 1,150 mm after growing to at least 2,900 mm. The development from instar 1 to instar 2 lasts less than one day. [1]

 

On the whole, Tunga penetrans does not do very well in terms of its Darwinian fitness. In a laboratory setting in which different mediums were provided for larval growth, the rate of survival from egg to adult in the best medium was 1.05%. Only 15% of the eggs were found to develop into larvae, and of those, only 14% formed a cocoon. Moreover, only half of the pupae reached the adult phase, resulting in a gender disequilibrium. [1] Although these results reflect a laboratory setting, the general lack of success for T. penetrans’s K-strategy is surprising given the number of fleas that a single person can attract. The low survival suggests that a concentrated public health effort directed at any point in the flea’s life cycle is likely to deal a crippling blow to the overall population of the flea in the area.

 

Morphology

 

This is an image of a generic flea. Although it is not Tunga penetrans, the illustration has all the major parts labeled.

Taken from phil.cdc.gov [21]

 

In a study of 1000 freshly-ejected T. penetrans eggs, it was found that females are generally smaller than males for all criteria. In some cases though, females had a bigger epipharynx and maxillar palpus. Due to its burrowing activity, the chigoe flea has developed a well-developed lacinia and epipharynx that is used to penetrate the skin. Overall, the fleas’ head is relatively flattened, which again aids in burrowing through the epidermal and dermal layers. [1, 21]

 

Investigators have also found that adult T. penetrans have different morphologies with respect to the shape of their head. Some have a rounded head, others have head shapes that resemble ski ramps more than anything else; still others demonstrate head shapes that are very linear with a slight bulge at the nose. These morphologies were seen to be host-specific, as only fleas of some head-types were found in specific hosts. This, along with genetic differences among the T. penetrans fleas that infect different host animals, may suggest that there are several species of closely related species have been grouped taxonomically under one binomial nomanclature. [1]

 

This is an SEM of the adult male and female Tunga penetrans fleas. The protruding copulatory organs of the male can be seen, as well as the shortened rear end of the female where, through a groove (not shown), copulation will occur. The male exhibits the ski-jump like head formation discussed above.

Provided via email by Prof. Heinz Melhorn from his book, Encycopedia of Parasitology 3rd. Ed. Springer, New York, 2008. [17,22]

 

Though the chigoe flea resembles most others in morphology, the flea has a hypertrophic region between tergites 2 and 3. As stated in Eisele et al (2003), tergites 2 and 3, as well as the abdominal sternites, stretch considerably and are bent apart. Chitinous clasps that are built for the abdominal enlargement surround these regions and hold onto the hypertrophic zone, giving them the appearance of a three-leafed clover. (See image 7 of the life cycle diagram.) Surprisingly, the rest of the flea, including the head and the thorax, do not change in shape. [1,11]

 

With the rapid expansion of the flea, the morphology of the flea is now vastly different. It has gone from the smallest flea in the world to a bulging mass that measures 5-10mm in diameter. This results in a volume that is 2000 to 3000 times what it used to be. [11]

 

Diagnostic Tests

 

There are no diagnostic tests for T. penetrans. This is most likely because the parasite is ectoparasitic with visible symptoms. Moreover, no literature was found to indicate that such a test was available. Again, due to the inefficiency and the uselessness of such a test, it is doubtful one would be needed to confirm diagnosis. Identification of the parasite through removal, and a patient’s traveling history, should suffice for diagnosis, though the latter is clearly more useful than the former. Localization of the lesion may be a useful diagnostic method for the clinician. A biopsy may be done, though again, is it not required for diagnosis. [5]

 

Management and Therapy

 

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 surgical extraction of the flea 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. [5]

 

There is no drug that has proven to be effective against embedded fleas. Oral niridazole was once considered a therapeutic drug, but well-designed studies are lacking and, given the severe adverse effects, this is one drug that is likely to cause more harm than good. However, it has some anecdotal evidence of lysing the fleas altogether. [2] Oral ivermectin is considered by some in endemic areas to be a panacea against the fleas but studies using high doses have failed to validate this hypothesis. Other drugs such as topical ivermectin and metrifonate have been somewhat successful, but not enough to be significant. [2,5] For superinfections, trimethoprim, sulfamethoxozaole, metronidazole, amoxicillin, and clavulnate have been used successfully, though these treat only secondary infections. [9]

 

Successful topical treatments also include cyrotherapy and electrodesiccation of the lesion. If formaldehyde, chloroform, or DDT are used topically, care should be taken when dealing with the resulting morbidity. The T. penetrans flea can also be suffocated using occlusive petrolatum, while Vaseline will kill the organism as well, most likely due to suffocation as the stigmatas would be covered. [2] The gum of the mammee apple, a fruit that also goes by the name Saint Domingo Apricot, has also been used to kill the chigoe flea, though this has not been reported in the main T. penetrans literature. [23]

 

Discussion of Public Health, Prevention Strategies, and a Case Study of Mexico

 

Due to the high number of hosts, eradication of tungiasis is not feasible, at least not easily so. Public health and prevention strategies should then be done with elimination as the target. As stated before, the poor K-strategy should allow for a targeted public health campaign to weaken the incidence rate of tungiasis. Better household hygiene, including having a cemented rather than a sand floor, and washing it often, would lower the rates of tungiasis significantly.

 

Before (right) and after (right) pictures of the same two patients after 21 and 25 days on Zanzarin, respectively.

Image taken from Feldmeier et al (2006). © Elsevier 2006. [24]

 

Though vaccines would be useful, due to the ectoparasitic nature of chigoe flea, they are neither a feasible nor an effective tool against tungiasis. Nevertheless, due to the high incidence of secondary infection, those at risk of tungiasis should get vaccinated against tetanus. A better approach is to use repellents that specifically target the chigoe flea. One very successful repellent is called Zanzarin, a derivative of coconut oil, jojoba oil, and aloe vera. In a recent study involving two cohorts, the infestation rates dropped 92% on average for the first one and 90% for the other. Likewise, the intensity of the cohorts dropped by 86% and 87% respectively. The non-toxic nature of Zanzarin, combined with its “remarkable regression of the clinical pathology” make this a tenable public health tool against tungiasis. [24]

 

The use of pesticide, like DDT, has also led to elimination of the Tunga penetrans, but this control/prevention strategy should be very carefully, if at all, because of the possible side effects such pesticides can have on the greater biosphere. In the 1950’s, there was a worldwide effort to eradicate malaria. As part of that effort, Mexico launched the CampaĖa Nacional para la Erradicación de Paludismo, or the National Campaign for the Eradication of Malaria. By spraying DDT in homes, the Anopheles genus of mosquitoes known to carry the deadly Plasmodium falciprarum and its other malarial cousin pathogens was mostly eliminated. As a consequence of this national campaign, other arthropods were either eliminated or significantly reduced in number, including the reduviid big responsible for Chagas’s disease (American Trypanosomiasis) and T. penetrans. [25] For clarity’s sake, it should be noted that 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. [26]

 

While other species gradually gained resistance to DDT and other insecticides that were used, T. penetrans did not; as a result, incidences of tungiasis in Mexico are 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%. [5] In fact, there was a 40-year period where there were 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. [25]

 

Rates of tungiasis were further reduced with the coincidental rise of shoes (as opposed to  sandals). [25] Though the use of socks and shoes can provide some measure of protection, it is unrealistic as a solution as neither eradication nor elimination of the parasite will occur. Nevertheless, social efforts to improve hygiene, welfare, and standard of living do provide additional protection against the chigoe flea as tungiasis is mostly a disease of the poor. Through increased efforts aimed at socio-economic improvements, coupled with the use of repellants, insecticides, and knowledge of proper extraction techniques, tungiasis has the potential to be overcome and defeated, finally ending the life of a disease that has plagued the poor all too often.

 

Useful Web Links

 

The curious reader is referred to these useful web links for information on tungiasis:

 

http://emedicine.medscape.com/article/1109335-overview

http://www.ajtmh.org/cgi/content/full/72/2/145

http://www3.interscience.wiley.com/cgi-bin/fulltext/118926772/HTMLSTART

http://www.springerlink.com/content/e3515q55028m8054/ (by subscription)

http://www.springerlink.com/content/j1wpn7jtlxm6ketj/?p=9c35517ae80743098ef50aec88672c36&pi=2 (by subscription)

 

Resources

 

[1] Nagy N, Abari E, D’Haese J, Calheiros C, Heukelbach J, Menche N, Feldmeier H, Mehlhorn H  "Investigations on the Life Cycle and Morphology of Tunga penetrans in

     Brazil." Parasitology Research 101.Supplement 2 (2007): 233-242.

 Springer-Verlag, 2007. SpringerLink.. 22 Feb. 2009 <http://www.springerlink.com/content/

     e3515q55028m8054/>.

 

[2] Gibbs, Neil F. "Tungiasis." eMedicine. 6 Jan. 2009. WedMD. 22 Feb. 2009

     <http://emedicine.medscape.com/article/1109335-overview>.

 

[3] Heukelbach, Jorg. Tungiasis. Sept. 2004. Orphanet.com. 23 Feb. 2009 <www.orpha.net/data/patho/GB/uk-Tungiasis.pdf>.

 

[4]"Tungiasis <Worldwide>.” www.gideononline.com.

 

[5] Heukelbach, Jorg. "Invited Review - Tungiasis." Revista do Instituto de Medicina

     Tropical de Sčo Paulo 47.6 (2005): 307-313.

 

[6]Drisdelle, Rosemary. "Chiggers - Parastic Mites." Suite101.com. 15 Mar. 2007. 22

     Feb. 2009 <http://insects.suite101.com/article.cfm/

     chiggers_parasitic_mites>.

 

[7]Medvedev, S. G. "Tunga penetrans (Chigoe Flea)." ZipCodeZoo.com. 21 Nov. 2005.

     22 Feb. 2009 <http://zipcodezoo.com/Animals/T/Tunga_penetrans/>.

 

[8] Darmstadt G, Francis J. "Tungiasis in a Young Child Adopted from South America."

     Pediatric Infectious Disease Journal 19.5 (2005): 485-487. The Pediatric

     Infectious Diseases Journal. 22 Feb. 2009 <http://www.pidj.org/pt/re/

     pidj/abstract.00006454-  

     20000500000017.htm;jsessionid=JhPGfnPhJmpHLpjb5M8kQYfvVtGvTm2L

     8xNK1dchm9FncQWqLfZX!-1429555639!181195629!8091!-1>.

 

[9] J. Joseph, J. Bazile, J. Mutter, S. Shin, A. Ruddle, L. Ivers, E. Lyon, P. Farmer. "Tungiasis in rural Haiti: a community-based response."

     Transactions of the Royal Society of Tropical Medicine and Hygiene

     100.10 (2006): 970-974. 22 Feb. 2009 <http://www.sciencedirect.com/

     science?_ob=ArticleURL&_udi=B75GP-4JDMV3R-1&_user=145269&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000012078&_version=1&_urlVersion=0&_userid=145269&md5=a9

     c1fd8aa072c4c30d4cd52ab883107d>.

 

[10] R. Hoeppli, “Early references to the occurrence of Tunga penetrans in tropical Africa,” Acta. Trop. 20 (1963), pp. 142–152

 

[11] Eisele M, Heukelbach J, Van Marck E, Mehlhorn H, Meckes O, Franck S, Feldmeier H. "Investigations on the biology, epidemiology, pathology

     and control of Tunga penetrans in Brazil: I. Natural history of tungiasis in

     man ." Parasitology Research 90.2 (2003): 87-99. Springer-Verlag, 2003. SpringerLink. 22 Feb. 2009   <http://www.springerlink.com/content/j1wpn7jtlxm6ketj/?p=9c35517ae80743098ef50aec88672c36&pi=2 >.

 

[12] Heukelbach J, Wilcke T, Harms G, Feldmeier H. "Seasonal Variation of Tungiasis in an Endemic Community." American

     Journal of Tropical Medicine and Hygiene 72.2 (2005): 145-149. The American

     Society of Tropical Medicine and Hygiene. 22 Feb. 2009

     <http://www.ajtmh.org/cgi/content/full/72/2/145>.

 

[13]"[Tungiasis: Worldwide Distribution] (source, GIDEON www.GIDEONonline.com)".

 

[14] Sanusi ID, Brown EB, Shepard TG, Grafton WD. “Tungiasis: report of one case and review of the 14 cases in the United States.” Journal of the American Academy of Dermatology 1989; 20: 941-944.

 

[15] Feldmeier, Hermann. "Tungiasis Research." E-mail to Fausto Bustos. 12 Feb. 2009.

 

[16]"Tungiasis." Health In Plain English. 23 Feb. 2009

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