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Infestations, insect bites, and stings
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
This is caused by the parasite Onchocerca volvulus and is found in equatorial West Africa. The disorder is spread by the bite of the blackfly Simulium damnosum, which is found around rivers. The larval forms, known as microfilariae, are injected into the skin by the blackfly and develop after some years into adult onchocercal worms. These are extremely long (up to 1 m) but very thin (1–2 mm in diameter) creatures that live curled up in the subcutis surrounded by a palpable, host-supplied fibrous capsule. The adult worm procreates by producing enormous numbers of microfilariae, which invade the subcutis of large areas of truncal skin.
Infestations, insect bites and stings
Published in Ronald Marks, Richard Motley, Common Skin Diseases, 2019
This is caused by the parasite Onchocerca volvulus and is found in equatorial West Africa. The disorder is spread by the bite of the blackfly Simulium damnosum, which is found around rivers. The larval forms, known as microfilariae, are injected into the skin by the blackfly and develop after some years into adult onchocercal worms. These are extremely long (up to 1 m) but very thin (1–2 mm in diameter) creatures that live curled up in the subcutis surrounded by a palpable, host-supplied fibrous capsule. The adult worm procreates by producing enormous numbers of microfilariae, which invade the subcutis of large areas of truncal skin.
The Diseases – Malaria, Filariasis and Dengue
Published in Jacques Derek Charlwood, The Ecology of Malaria Vectors, 2019
Transmission to the mosquito is also inefficient. Microfilariae that are ingested have to pass through the cibarial armature of the mosquito, which act as a first line of defence against them. In anopheline mosquitoes, the pharyngeal armature is well developed, so that microfilariae are damaged when they are ingested. In Anopheles mosquitoes, the proportion of microfilariae that reaches the L3 stage increases as the number of ingested microfilariae increases (facilitation). Low densities of microfilariae are associated with a much lower rate of development to L3. In contrast, in Aedes vectors of filariasis, low densities of ingested microfilariae have a high likelihood of survival but, the proportion of ingested microfilariae that survive to become L3 larvae decreases as more microfilariae are ingested, a process known as limitation. Only a limited number of microfilariae develop in the mosquito. As with malaria, the mosquito has to survive through the developmental time of the parasite, which may be 10–12 days depending on temperature. The larvae leave the mosquito during feeding and are deposited on the skin of the host, rather than inside the host like malaria parasites. This also reduces the likelihood of successful transmission, and once a mosquito has shed its microfilariae it reverts to being uninfected and uninfectious.
Deciphering the anti-filarial potential of bioactive compounds from Ocimum sanctum: a combined experimental and computational study
Published in Pharmaceutical Biology, 2022
Ayushi Mishra, Vipin Kumar, Anchal Singh
LF infection results in severe pathologies like lymphedema, hydrocele, lymphangitis, elephantiasis, and tropical pulmonary eosinophilia. The WHO recommends IDA program (ivermectin, DEC and albendazole) for LF elimination and control. These drugs are only effective against microfilariae and have negligible effect on adult worms. The IDA treatment is often associated with various side effects like transient fever, headache, dizziness, malaise, myalgia, fatigue, and gastrointestinal problems (Budge et al. 2018). Less common side effects are cough, dyspnoea, blood-tinged sputum, bronchoconstriction, urticaria, haematuria, etc. DEC is reported to cause loss of vision and fatal encephalopathy when given to the patients co-infected with onchocerciasis or loiasis (Fischer et al. 2017; Gobbi et al. 2019). Several reports describe ivermectin related serious adverse drug reactions (SADRs) including liver and kidney dysfunction (Ampillo et al. 2021). Therefore, anti-filarial drugs that are effective against adult filarial worms are urgently needed for LF treatment.
Lymphatic filariasis vaccine development: neglected for how long?
Published in Expert Review of Vaccines, 2021
Vivek P Chavda, Anjali Pandya, Sreeranjini Pulakkat, Moinuddin Soniwala, Vandana Patravale
The detection of microfilariae in a blood smear is the primary mode for the diagnosis of active infection; however, approximately 40–60% of individuals do not secrete MF although they harbor adult worms. At night, the microfilariae that induce LF travel in the bloodstream (called nocturnal periodicity), and thus, blood must be collected at night, when the microfilariae are most active, and a dense smear should be produced and dyed with giemsa. Serologic approaches, in addition to the microscopic determination of microfilariae, can be used to diagnose LF [11]. Antifilarial IgG4 serum concentrations of patients with symptomatic filarial infection are frequently increased, and they may be identified using conventional tests [12]. Since lymphedema can develop several years following infection, lab testing in such patients is mostly negative. Numerous robust, precise, cost-effective, and field-applicable diagnostic approaches have been developed in recent years using a variety of clinical, parasitological, immunological, and molecular markers as screening methods (Figure 2) [13]. Loop-Mediated Isothermal Amplification (LAMP) assay is a new molecular diagnostic tool with rapid and semi quantitative estimation for L. loa microfilaria.
Development of a recombinant vaccine against human onchocerciasis
Published in Expert Review of Vaccines, 2021
David Abraham, John Graham-Brown, Darrick Carter, Sean A. Gray, Jessica A. Hess, Benjamin L. Makepeace, Sara Lustigman
The feasibility of an anti-O. volvulus larvae vaccine is supported by uncovering two distinctive expressions of anti-L3 protective immunity within the O. volvulus endemic population: (1) Immunity that impedes the development of patent infections (microfilaria positive) in the putatively immune (PI) individuals (i.e. individuals that had no clinical manifestations of the disease, even though they lived for at least 10 years within regions where onchocerciasis is endemic and were exposed to high transmission rates of infection) [54–57]; (2) Concomitant immunity to O. volvulus L3, which develops in the patently infected (INF) individuals with increasing age and is independent of the immune responses that are induced by the adult worms and microfilariae associated with patent infection. Concomitant immunity prevents most of the newly acquired L3 infections from developing and results in a stable adult worm burden in the INF [18,58,59]. This immunity is not directed against the adult or the microfilaria stages of the parasite. Some of the mechanisms of acquired protective immunity against O. volvulus infection in humans (reviewed in [45,60,61]) were shown to be associated with their ability to mount mixed Th1/Th2 responses against O. volvulus L3 and/or molting L3 [57,59], as well as the presence of cytophilic antibodies that together with the cytokines produced, induce efficient anti-L3 antibody-dependent cell mediated cytotoxicity (ADCC) reactions against L3 [59,62–70].