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Human myiasis in Sub-Saharan Africa: A systematic review [1]

['Binta J. J. Jallow', 'Central South University', 'Department Of Medical Parasitology', 'Changsha City', 'Goudja Gassara', 'Department Of Nutrition Science', 'Food Hygiene', 'Xiangya School Of Public Health', 'Ousman Bajinka', 'University Of The Gambia']

Date: 2024-04

The findings of this study reveals that international travelers to Sub-Saharan Africa were mostly infested therefore, we recommend that both international travelers and natives of SSA be enlightened by public health officers about the disease and its risk factors at entry points in SSA and the community level respectively. Clinicians in Sub-Saharan Africa often misdiagnose the disease and most of them lack the expertise to properly identify larvae, so we recommend the extensive use of molecular identification methods instead.

In total, 157 cases of human myiasis in SSA were reviewed. Eleven fly species (Cordylobia anthropophaga, Cordylobia rodhaini, Dermatobia hominis, Lucilia cuprina, Lucilia sericata, Oestrus ovis, Sarcophaga spp., Sarcophaga nodosa, Chrysomya megacephala, Chrysomya chloropyga and Clogmia albipuntum) were found to cause human myiasis in SSA. Cordylobia anthropophaga was the most prevalent myiasis-causing species of the reported cases (n = 104, 66.2%). More than half of the reported cases were from travelers returning from SSA (n = 122, 77.7%). Cutaneous myiasis was the most common clinical presentation of the disease (n = 86, 54.7%). Females were more infected (n = 78, 49.6%) than males, and there was a higher infestation in adults than young children.

Here, we collect cases of human myiasis in Sub-Saharan Africa based on literature retrieved from PubMed, Google Scholar and Science Direct from 1959 to 2022. A total of 75 articles and 157 cases were included in the study. The recommendations of PRISMA 2020 were used for the realization of this systematic review.

Human myiasis is a parasitic dipteran fly infestation that infects humans and vertebrates worldwide. However, the disease is endemic in Sub-Saharan Africa and Latin America. In Sub-Saharan Africa, it is under-reported and therefore its prevalence is unknown. This systematic review aims to elucidate the prevalence of human myiasis, factors that influence the infection, and myiasis-causing fly species in SSA. The review also dwelled on the common myiasis types and treatment methods of human myiasis.

Human myiasis is a neglected tropical disease in the world especially in SSA. Human myiasis in SSA has infects patients from all dynamics especially those with underlying health issues like primary wounds. The disease can be fatal especially when it involves heavy infestation of the scalp (migratory myiasis) among young children. Subcutaneous myiasis of the eye and genitals can be devastating for patients and can lead to damage in these areas if the disease is misdiagnosed and larvae removal is delayed. The findings and recommendations in our study can be used by government officials in SSA to provide hospitals with state-of-the-art diagnostic tools, trained entomologists, and research funding to comprehensively study human myiasis. Public health officers at entry points in SSA should inform international travelers about the risk factors of the disease and common preventive measures. Clinicians in SSA should report more human myiasis cases to enable researchers to estimate the epidemiology and prevalence of the disease. The natives of SSA should be enlighten more on the symptoms and risk factors of the disease and encourage them to report to health facilities when they experience these symptoms.

1. Introduction

Myiasis, coined from the Greek word ‘myia’ meaning fly, is the infestation of live or dead tissues of vertebrates (humans and animals) by immature stages (maggots) of dipteran flies [1,2]. The disease dates back to 1840 when it was first described by Hope [3] and is still considered a neglected disease in humans, especially in the tropical and sub-tropical regions in SSA, Asia, and Latin America [4]. The disease has a worldwide distribution and has been endemic in Latin America and SSA for years. However, with the increase in global travel, the disease has spread widely, especially in areas with warmer temperatures and high humidity [5]. Myiasis is more common in animals, such as sheep, rodents, and antelope, than humans because humans are accidental hosts. Furuncular myiasis is the most common myiasis reported from travelers returning from endemic regions and is usually caused by the human botfly, Dermatobia hominis in Latin America. In SSA, the tumbu fly or mango fly (Cordylobia anthropophaga) causes year-round infestation which could be dated back to 1904 [6], albeit most of the human myiasis infestation in SSA are caused by this species [7]. The climate condition in SSA is suitable for the breeding of some fly species which makes most places to be endemic of them. Although human myiasis is endemic in SSA, the diversity and prevalence of myiasis-causing flies in SSA is still not clear to date.

Human myiasis can be categorized depending on several factors. According to the host-parasitic relationship (feeding relationship between larva and the host), myiasis can be divided into obligatory myiasis, facultative myiasis, and accidental myiasis. In obligatory myiasis, fly larvae require living tissues for survival and to complete the immature stages of their life cycle. Facultative myiasis on the other hand is caused by free-living fly species (feeding on decaying organic matter and can opportunistically infest living tissues), their larvae do not require a living host to complete their life cycle. While accidental myiasis is a condition in which the larval stages of dipteran flies are accidentally ingested through contaminated food or water [8,9]. Additionally, human myiasis can further be classified into primary and secondary myiasis. When dipteran fly larvae invade healthy tissues or skin it will result in primary myiasis, and when these larvae colonize pre-existing wounds it will result in secondary myiasis [4,10].

According to the anatomical site or clinical presentation, myiasis can be cutaneous which involves the infestation of dermal and sub-dermal layers (tissues) of the skin (humans and animals) or infest any part of the body (nose, eyes, scalp, breast, intestine, leg, urogenital, mouth, arms, and thighs) [11]. Cutaneous myiasis takes account the largest part of clinical presentation in humans which could be categorized into migratory (creeping) myiasis, furuncular myiasis, and wound (traumatic) myiasis [Fig 1] [12]. Similarly, furuncular myiasis is the most common type reported from travelers from endemic regions, and is characterized by the formation of a painful inflammatory nodule with a central punctum on healthy or unbroken skin [1]. It is mainly caused by the tumbu fly or the botfly [13]. Wound (traumatic) myiasis is caused by dipteran fly larvae which colonize pre-existing wounds and enlarge them [8,10]. While migratory (creeping) myiasis is a condition in which dipteran fly larvae burrow in the subcutaneous tissues of the host and migrate, and often causes pruritic lesions within the host tissues. Theppote A., et al., 2020 presented a clinical presentation of cutaneous myiasis [12].

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TIFF original image Download: Fig 1. Life cycle of Cordylobia anthropophaga. 1. Adult female Cordylobia anthropophaga lay 100–300 eggs on the on wet clothing or faecal-contaminated soil. 2. Eggs catch to form 1st instar larva d. 3. 1st instar larva penetrates a host which is usually dog, or rodent, but could accidently penetrate a human host and develop to 3rd instar larva. 4. Larva leaves its host to the ground to pupate. 5. pupa metamorphosis to an adult fly. https://doi.org/10.1371/journal.pntd.0012027.g001

Compelling scientific literature have revealed that a significant rise in temperature or humidity will increase the growth and redistribution of most myiasis-causing flies, subsequently increasing myiasis infestation in such regions [11,14]. Some factors that influence this dermatosis in SSA are high humidity and temperature (especially during the rainy season) [5]. Poverty, and poor hygiene also add to the vulnerability to human myiasis infestation. Rodents, antelopes, and pet animals, especially dogs, are the hosts of tumbu fly, making farmers, and pet keepers more vulnerable to C. anthropophaga infestation [15,16]. Skin-related diseases belong to the leading travel-related health problems reported. Currently, human myiasis is reported as one of the five most common travel-related skin diseases, which accounts for 7–12% of travel-related diseases globally [1,17]. Hence, an increase in international travel will drastically increase human myiasis infestation in both endemic and non-endemic regions.

Human myiasis can affect people (tourists, businesspersons, etc.) traveling to endemic regions, especially in SSA, where it remains a burden and needs urgent attention. Both travelers and natives of SSA lack awareness of how to prevent themselves against human myiasis infestation which adds to the vulnerability of the disease. Wearing long garments to cover legs and hands, especially during the rainy season, and sleeping in bed nets would help prevent insect bites. Lying on the ground, hanging clothes on shady lines or bushes, and lack of ironing of garments or bedding after laundry should be avoided [17]. The use of some fly repellents is encouraged to avoid insect bites. Open wounds should be routinely dressed, good skincare and standard hygiene should be maintained to avoid human myiasis infestation [16]. Animal pets should be properly handled because some of these pets can be reservoirs for the disease and can add to the vulnerability of human myiasis infestation.

This parasitological condition causes harm not only to humans but also to the livestock industry, accruing substantial economic losses for farmers [8,18]. Human myiasis is often misdiagnosed as cellulitis, leishmaniasis, tungiasis, or furunculosis [19] which is a common problem in diagnosing the disease. Therefore, properly extracting fly maggots, and sometimes the use of antibiotics becomes the gold standard for the treatment of human myiasis cases. Morphological identification is considered standard for larval identification in human myiasis cases, however, the use of molecular identification method has been being utilized globally. This method can differentiate closely related species and identify immature stages which could be an effective method in cases where traditional morphological method is ineffective [1,20,21]. Secondary bacterial superinfection and tetanus are some of the severe complications of human myiasis especially if larvae fragmentation occurs during removal [16,21,22]. Subsequently, the need to systematically review the current literature on human myiasis in SSA is an important priority. This review aims to elucidate the prevalence of human myiasis, and highlight the most common myiasis-causing flies and areas where they are endemic in SSA. We wish to uncover the predisposing factors of human myiasis in SSA and highlight the most common clinical forms of myiasis. Our study will equally highlight the common extraction and treatment forms of human myiasis.

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[1] Url: https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0012027

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