We searched PubMed, and included all publications with “Loa loa” or “loiasis” in the title. Non-English publications were included as far as they were indexed in PubMed. Because some non-English, and some earlier literature, used different spelling, the terms “loaiasis” and “Filaria loa” were added to the search. References were subjectively labelled by the two authors in categories: epidemiology, diagnosis, treatment, vector studies, animal models, host parasite interactions, case reports,
Personal ViewLoa loa—does it deserve to be neglected?
Introduction
The startling feature of infection with Loa loa filariae is vividly depicted in an early report:1 “…a single woman, aged 29, attended Dr O'Donovan's clinic at the London Hospital on December 17, 1930. Fifteen months ago she went to the coastal area of Nigeria as a missionary…on the boat returning to this country she noticed in a mirror a white worm about one inch long moving in the skin of the cheek toward the inner canthus of the left eye. …she was advised…to apply pressure to prevent the worm from entering the eye, and when she did so the worm retreated and disappeared.” For many years, reports described the subconjunctival passage of the eye worm through the patient's eye (figure 1). Together with the so-called Calabar swelling, this is the visible and pathognomonic symptom of loiasis. Since its first description by a French surgeon located in Santo Domingo in 1770,2 L loa has been a popular topic for case reports of rare diseases.
14·4 million people live in high-risk regions, which are defined as an area where the estimated prevalence of eye worm is greater than 40%, and 15·2 million people live in intermediate risk areas with an estimated prevalence around 30% (20–40%). From these figures, we estimate that at least 10 million people are infected with L loa. The endemic countries are: Angola, Cameroon, Central African Republic, Chad, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Nigeria, Republic of Congo, and Sudan.3 In some endemic regions loiasis is the second or third most common cause of medical consultations.4, 5
On the basis of our clinical experience in Gabon, we postulated that L loa might not be as harmless as commonly suggested. We searched the literature to identify research needs and propose topics that can be addressed by future research programmes. The earliest reference was from the year 1918.6 Many published articles had been written not because loiasis was the main focus of scientific interest, but the attention was drawn to L loa by other research. For example, when bacteria of the genus Wolbachia were found to have a mutualistic relationship with some filarial nematodes, three research groups were looking independently for the bacteria in L loa worms; none found them.7, 8, 9 In other studies, awareness of L loa increased as a result of serious adverse events to ivermectin—especially encephalopathies—in patients who were treated for Onchocerca volvulus while co-infected with L loa. Then, a series of articles were published on L loa treatment10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 and epidemiology.22, 23, 24, 25, 26 Consequently, the number of publications on L loa increased substantially in the past 20 years.
Section snippets
Epidemiology and diagnosis
The first comprehensive literature review on L loa epidemiology was published in 1997.27 From 2002 to 2010, a large effort was made to assess L loa prevalence using large-scale surveys that implemented a short questionnaire for the history of eye worm (rapid assessment procedures for loiasis, RAPLOA). Of the ten countries with endemic L loa, Gabon and Equatorial Guinea were classified as high risk, with an estimated prevalence of eye worm history greater than 40% and representing a large
Disease treatment
The WHO-recommended first-line treatment of loiasis is diethylcarbamazine,31 which has been clinically studied in patients with onchocerciasis and lymphatic filariasis.32, 33 However, only one randomised controlled trial has investigated a prophylactic regimen in immunologically naive volunteers from the US Peace Corps,34 and we could find no trial on efficacy and adverse events of diethylcarbamazine treatment in patients from an endemic region with ongoing loiasis in our literature search.
Disease symptoms and burden
The range of loiasis symptoms and complications goes from no symptoms at all to various severe complications, such as cerebral (eg, encephalopathy in the absence of treatment), cardiac (eg, endomyocardial fibrosis), pulmonary (eg, pulmonary infiltrates), and renal complications (eg, renal failure), as well as neurological and psychiatric disorders. Many complications are presumably due to immune complex deposition and are frequently accompanied by marked eosinophilia.50, 51 Most publications
Conclusions
The chronic nature of infection, range of symptoms and complications, treatment complications, comorbidity, and economic restrictions mean that large, standardised, and longitudinal studies would be needed to assess fully the effect of L loa on affected populations. Such studies would be complex and might not be cost-efficient. We suspect that the paucity of data is evidence that the disease is viewed as less serious than it really is, and, vice versa—because the disease is thought to be less
Search strategy and selection criteria
References (65)
Loa loa—a neglected filaria
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Retinal hemorrhages after ivermectin treatment for onchocerciasis in a patient with Loa loa microfilaremia
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Serious reactions after mass treatment of onchocerciasis with ivermectin in an area endemic for Loa loa infection
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Integrated rapid mapping of onchocerciasis and loiasis in the Democratic Republic of Congo: impact on control strategies
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Encephalopathy following Loa loa treatment with albendazole
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Randomized, controlled, double-blind trial with ivermectin on Loa loa microfilaraemia: efficacy of a low dose versus current standard dose
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Sur un ver trouvé sous la conjonctive à Maribarou, isle Saint-Dominique
J Med Chir Pharm Paris
The geographic distribution of Loa loa in Africa: results of large-scale implementation of the Rapid Assessment Procedure for Loiasis (RAPLOA)
PLoS Negl Trop Dis
Encephalite au cours du traitment de la filariose a Loa loa par la diethylcarbamazine. A propos de 6 observations
Bull Soc Pathol Exot
Removal of worm (filaria loa) from the eye
BMJ
No evidence of Wolbachia endosymbiosis with Loa loa and Mansonella perstans
Parasitol Res
Obligatory symbiotic Wolbachia endobacteria are absent from Loa loa
Filaria J
Evidence against Wolbachia symbiosis in Loa loa
Filaria J
Analysis of the mdr-1 gene in patients co-infected with Onchocerca volvulus and Loa loa who experienced a post-ivermectin serious adverse event
Am J Trop Med Hyg
Macrofilaricidal activity after doxycycline only treatment of Onchocerca volvulus in an area of Loa loa co-endemicity: a randomized controlled trial
PLoS Negl Trop Dis
Loa loa encephalopathy temporally related to ivermectin administration reported from onchocerciasis mass treatment programs from 1989 to 2001: implications for the future
Filaria J
Overview: report of a Scientific Working Group on Serious Adverse Events following Mectizan(R) treatment of onchocerciasis in Loa loa endemic areas
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Report of a Scientific Working Group on Serious Adverse Events following Mectizan(R) treatment of onchocerciasis in Loa loa endemic areas
Filaria J
Three probable cases of Loa loa encephalopathy following ivermectin treatment for onchocerciasis
Am J Trop Med Hyg
Community-directed delivery of doxycycline for the treatment of onchocerciasis in areas of co-endemicity with loiasis in Cameroon
Parasit Vectors
Adverse reactions from community directed treatment with ivermectin (CDTI) for onchocerciasis and loiasis in Ondo State, Nigeria
Rev Biol Trop
Programmatic and communication issues in relation to serious adverse events following ivermectin treatment in areas co-endemic for onchocerciasis and loiasis
Filaria J
Variation in incidence of serious adverse events after onchocerciasis treatment with ivermectin in areas of Cameroon co-endemic for loiasis
Trop Med Int Health
Co-infection with Onchocerca volvulus and Loa loa microfilariae in central Cameroon: are these two species interacting?
Parasitology
Mapping the distribution of Loa loa in Cameroon in support of the African Programme for Onchocerciasis Control
Filaria J
Epidemiology of concomitant infections due to Loa loa, Mansonella perstans, and Onchocerca volvulus in rain forest villages of Cameroon
Med Microbiol Immunol
Combined utilisation of Rapid Assessment Procedures for Loiasis (RAPLOA) and Onchocerciasis (REA) in rain forest villages of Cameroon
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Cited by (59)
The African eye worm: current understanding of the epidemiology, clinical disease, and treatment of loiasis
2024, The Lancet Infectious DiseasesCases of Loiasis Among a Congolese Family: Screening for Loiasis Among Newly Arrived Refugees From Endemic Areas
2023, Journal for Nurse PractitionersA call for loiasis to be added to the WHO list of neglected tropical diseases
2022, The Lancet Infectious DiseasesCitation Excerpt :A Personal View published in The Lancet Infectious Diseases1 in 2014 posed the question “does [loiasis] deserve to be neglected?”
Spleen nodules in Loa loa infection: re-emerging knowledge and future perspectives
2022, The Lancet Infectious DiseasesPreliminary comparison between an in-house real-time PCR vs microscopy for the diagnosis of Loa loa and Mansonella perstans
2021, Acta TropicaCitation Excerpt :Infections with the filarial nematodes Loa loa and Mansonella perstans are among the most neglected filarial infections. L. loa is endemic in 11 countries of Central and West Africa and loiasis is estimated to affect about 20 million people (Metzger and Mordmüller, 2014; Molyneux, 2009). M. perstans infection is widespread in more than 30 countries of sub-Saharan Africa, while sporadic cases have been reported in Latin America, mostly in the Caribbean and along the Atlantic coast.
Burden of disease in Gabon caused by loiasis: a cross-sectional survey
2020, The Lancet Infectious DiseasesCitation Excerpt :The RAPLOA questionnaire, comprised of questions regarding subconjunctival migration of adult worms, was shown to correlate well with hypermicrofilaraemia prevalence in communities, although the sensitivity and specificity of the questionnaire for the diagnosis of individual patients with loiasis is unknown.17 Calabar swelling, defined as transient non-pitting oedema above joints has been previously correlated with loiasis.1,12 It is, however, less specific when correlated with microfilaraemia at a population level,17 as other diseases can cause similar signs and symptoms.