Ectoparasitosis

Human lice are blood-sucking insects that infest:

• Pediculus humanus capitis, the head 
• Pediculus humanus corporis, the body 
• Phthirus pubis, the pubic region

Pediculus humanus capitis: Of the three lice species affecting humans, the head louse is the most frequent. Pediculosis of the head affects millions of school-age children all over the world. In developing countries, prevalence of pediculosis in vulnerable parts of the population can be over 50% (1). Transmission is by close head-to-head contact and rarely through fomites such as hats, clothes, or pillowcases. Persistent infection is often associated with secondary infection of the scalp and is an important cause of impetigo in developing countries. Because of pruritus, subsequent sleep disturbances and difficulties in concentration, children with pediculosis capitis may perform poorly in school (2).

Pediculus humanus corporis: Body lice, which attach to clothes, are propagated when clothes are not washed or changed regularly, and usually affect homeless people, displaced persons, or prisoners in poor conditions. This body louse is feared as a vector for Rickettsia prowazekii (epidemic typhus), Borellia recurrentis (relapsing fever), and Bartonella quintana (trench fever). 

Pthirus pubis: Infests pubic hair and occasionally other hairy areas, such as eye lashes. Pubic lice are usually transmitted during intimate body contact, such as during sexual intercourse. Treatment must therefore include the patient's partner. Rash and pruritus are the most frequent symptoms (2).

References
1. Heukelbach J, Walton SF, Feldmeier H. Ectoparasitic infestations. Curr Infect Dis Rep [Internet]. 2005;7(5):373-80. Available from: http://www.ncbi.nlm.nih.gov/pubmed/16107235
2. Heukelbach J, Feldmeier H. Ectoparasites - The underestimated realm. Vol. 363, Lancet. 2004. p. 889-91.

Scabies, caused by the mite Sarcoptes scabiei var. hominis, leads to itching eruptions of the skin and is predominantly transmitted by person-to-person contact. The importance of transmission via fomites (e.g., clothes, towels, bed linen) depends on the setting. Scabies is particularly prevalent in resource-poor conditions and among children and is associated with insufficient access to healthcare. The predominant symptom of scabies is an intense pruritus, which disturbs the sleep and can be debilitating. Disruption of the skin's protective barrier function promotes secondary bacterial infections, which can lead to potentially life-threatening, complications such as post-streptococcal glomerulonephritis (1,2). Scabies impairs the life quality of children and adults alike.

The parasite burden of individuals with scabies is usually low. An average burden of 10-12 mites has been determined for the first 3 months of the infection. However, hundreds of mites can be found in neglected children in underprivileged communities, and millions in patients with crusted scabies (3).

Key facts

• Scabies mites infect up to 300 million people worldwide, most of whom are children living in poverty and overcrowded conditions (4).
• Scabies was responsible for 0.21% of DALYs from all conditions studied by Global Burden of Disease study in 2015 worldwide.
• The world regions of East Asia (age standardized DALYs 136.32), Southeast Asia (134.57), Oceania (120.34), tropical Latin America (99.94), and south Asia (69.41) had the greatest burden of DALYs from scabies.
• The burden of scabies is greater in tropical regions, especially in children, adolescents, and elderly people (2).
• In developing countries scabies is endemic in impoverished communities. In industrialized countries, outbreaks occur in hospitals, old people's homes, and other institutions.

More information

• Scratching the itch: is scabies a truly neglected disease?; 2017
• The global burden of scabies: a cross-sectional analysis from the Global Burden of Disease Study 2015; 2017

References
1. Heukelbach J, Walton SF, Feldmeier H. Ectoparasitic infestations. Curr Infect Dis Rep [Internet]. 2005;7(5):373-80. Available from: http://www.ncbi.nlm.nih.gov/pubmed/16107235
2. Karimkhani C, Colombara D V, Drucker AM, Norton SA, Hay R, Engelman D, et al. The global burden of scabies: a cross-sectional analysis from the Global Burden of Disease Study 2015. Lancet Infect Dis [Internet]. Elsevier; 2017 Dec 1 [cited 2017 Dec 28];17(12):1247-54. Available from: https://www.sciencedirect.com/science/article/pii/S1473309917304838
3. Heukelbach J, Feldmeier H. Scabies. Lancet [Internet]. Elsevier; 2006 May 27 [cited 2017 Dec 28];367(9524):1767-74. Available from: http://www.sciencedirect.com/science/article/pii/S0140673606687722
4. Kearns TM, Speare R, Cheng AC, McCarthy J, Carapetis JR, Holt DC, et al. Impact of an Ivermectin Mass Drug Administration on Scabies Prevalence in a Remote Australian Aboriginal Community. Vinetz JM, editor. PLoS Negl Trop Dis [Internet]. 2015 Oct 30 [cited 2017 Dec 28];9(10):e0004151. Available from: http://www.ncbi.nlm.nih.gov/pubmed/26516764

Tungiasis is a parasitic skin disease caused by the penetration of female sand fleas (Tunga penetrans; in some areas also T. trimamillata) into the skin. With less than 1mm T. penetrans is the smallest flea species known. The parasite burrows rapidly into the skin at the toes, the sole, the lateral rim of the foot or the heel. Ectopic penetration occurs in less than 1 %. Once embedded in the epidermis, the female flea increases its body volume by a factor of 2000 within two weeks. This is paralleled by an intense local inflammation resulting in difficulty walking. Bacterial superinfection of the lesions is almost constant, leading to the development of abscesses, suppuration or lymphangitis. Tungiasis is a zoonosis affecting humans and animals alike (1).

Around the world tungiasis has various local names including jiggers, chigoe, pique or nigua, indicating that the disease has been prevalent in many populations for a long time. Tungiasis occurs in endemic proportions among marginalized, resource-poor urban and rural communities in sub-Saharan Africa, South America and many several islands in the Caribbean (1). Prevalence may be up to 60% in children and 30% in the general populations. However, there is no data in any country of the accurate geographic distribution and age-specific prevalence. In most endemic areas transmission is seasonal, with the highest incidence during the dry season. When transmission occurs indoors, incident cases appear the whole year round (2).

Due to pain and itching, children have difficulties to concentrate on their lessons and have difficulty in sleeping and walking. Tungiasis has recently been demonstrated to significantly impair the quality of life of children. Infection is often associated with stigma, with victims being ridiculed, and they consequently isolate themselves. Since tungiasis impairs mobility and concentration, it impacts children's ability to learn and to get jobs. Similarly, tungiasis affects adults' ability to conduct their work, whether it be a paid job or on their own farm (2).

More information: Tungiasis: A Neglected Disease with Many Challenges for Global Public Health; 2014

References
1. Heukelbach J, Sales De Oliveira FA, Hesse G, Feldmeier H. Tungiasis: A neglected health problem of poor communities. Trop Med Int Heal. 2001;6(4):267-72. 
2. Elson L, Wright K, Swift J, Feldmeier H. Control of Tungiasis in Absence of a Roadmap: Grassroots and Global Approaches. Trop Med Infect Dis [Internet]. 2017;2(3):33. Available from: http://www.mdpi.com/2414-6366/2/3/33

Related News

• Current status of the knowledge on the epidemiology of tungiasis in the Americas | Versão em Português
• COURSE: Tungiasis – Sand Flea disease: Training of health workers at national and district levels on skin-NTDs

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Hookworm-related cutaneous larva migrans (Hr-CLM) is a parasitic skin disease caused by the penetration of feline or canine hookworm larvae into the human epidermis. The most frequent species are Ancylostoma braziliense, Ancylostoma caninum and Uncinaria stenocephala. In humans, the larva is unable to cross the basal membrane of the epidermis and migrates in the compartment of the epidermis until it dies spontaneously after a few weeks to several months. The migration of animal hookworm larvae causes a typical elevated erythematous linear or serpiginous track known as "creeping eruption ". Hr-CLM is associated with intense pruritus. The resulting scratching leads to denudation of the skin, which facilitates bacterial superinfection of the lesion. Additional skin injury may be caused by inappropriate surgical manipulation of the lesion and treatment with toxic substances (1,2).

The migration of hookworm larva in the skin causes an intense inflammation leading to persistent itching. Itching is so intense that patients cannot sleep normally. Lesions tend to become superinfected with pathogenic bacteria as a result of scratching. Staphylococcus aureus and streptococci are particularly common causes of super-infection of lesions. If lesions remain infected with group A streptococci for a prolonged period of time, post-streptococcal glomerulonephritis may ensue, eventually leading to renal insufficiency. Hr-CLM severely impedes the quality of life in adults as well as in children (3).

Whereas animal hookworm species parasitize dogs and cats worldwide, Hr-CLM is mainly seen in tropical and subtropical areas in South America, the Caribbean, Africa and South-East Asia. Sporadic cases have been reported in Europe. In semi-arid northeastern Brazil, prevalence ranged from 0.2% to 4.4% in the general population and from 0% to 14.9% in children <5 years. No population-based data exists for other endemic areas. Known risk factors are male sex, young age, living in a house without a solid floor and barefoot walking. An association with low income has been suspected (1). 

More information: Epidemiological and clinical characteristics of hookworm related cutaneous larva migrans; 2008

References
1. Reichert F, Pilger D, Schuster A, Lesshafft H, Guedes de Oliveira S, Ignatius R, et al. Prevalence and Risk Factors of Hookworm-Related Cutaneous Larva Migrans (HrCLM) in a Resource-Poor Community in Manaus, Brazil. Diemert DJ, editor. PLoS Negl Trop Dis [Internet]. 2016 Mar 24 [cited 2017 Dec 28];10(3):e0004514. Available from: http://www.ncbi.nlm.nih.gov/pubmed/27010204
2. Feldmeier H, Schuster A. Mini review: hookworm-related cutaneous larva migrans. Eur J Clin Microbiol Infect Dis [Internet]. 2012 Jun 16 [cited 2017 Dec 28];31(6):915-8. Available from: http://www.ncbi.nlm.nih.gov/pubmed/21922198
3. Schuster A, Lesshafft H, Talhari S, Guedes de Oliveira S, Ignatius R, Feldmeier H. Life Quality Impairment Caused by Hookworm-Related Cutaneous Larva Migrans in Resource-Poor Communities in Manaus, Brazil. Zhou X-N, editor. PLoS Negl Trop Dis [Internet]. Public Library of Science; 2011 Nov 8 [cited 2017 Dec 29];5(11):e1355. Available from: http://dx.plos.org/10.1371/journal.pntd.0001355