Neglected Tropical Diseases: The Global Burden of Overlooked Infections

• Parasitic-Neglected Tropical Diseases

Chagas disease (Trypanosoma cruzi)

Chagas disease, caused by Trypanosoma cruzi, is transmitted by triatomine bugs. Upon entering the bloodstream, T. cruzi undergoes intracellular differentiation into amastigotes, which invade cardiac myocytes and smooth muscle cells​ (16). The parasite's trans-sialidase enzymes facilitate immune evasion by altering host cell surface glycoproteins, allowing persistence in tissues ​(17). Chronic infection leads to inflammatory cardiomyopathy, characterised by fibrosis, arrhythmias, and progressive heart failure. Gastrointestinal complications such as megaoesophagus and megacolon occur due to autonomic nerve damage caused by persistent parasitic invasion ​(18). Antiparasitic treatment with benznidazole or nifurtimox is most effective during the acute phase of Chagas disease, aiming to eliminate the parasite and prevent chronic complications ​(10). 

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Onchocerciasis (Onchocerca volvulus) 

Onchocerciasis, or river blindness, is caused by Onchocerca volvulus and transmitted by blackflies (Simulium spp.). The infective larvae migrate into the dermis and subcutaneous tissues, where they mature into adult worms that release microfilariae. The host immune response to dying microfilariae triggers intense pruritus, skin atrophy, and progressive ocular damage. Chronic inflammation leads to sclerosing keratitis, optic nerve atrophy, and irreversible blindness​ (19). Ivermectin is administered annually or biannually to kill microfilariae and reduce skin and eye pathology; however, it does not kill adult worms, necessitating repeated treatments over several years ​(10). 

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• Viral-Neglected Tropical Diseases 

Dengue Virus (DENV) 

Dengue, caused by four serotypes of Dengue virus (DENV-1 to DENV-4), is transmitted ​by Aedes aegypti and Aedes albopictus mosquitoes ​(20). The virus enters monocytes and dendritic cells via Fc receptor-mediated endocytosis, triggering a cytokine storm and capillary leakage ​(21). Dengue haemorrhagic fever is driven by antibody-dependent enhancement, where non-neutralizing antibodies from a prior infection facilitate increased viral replication, leading to vascular permeability, thrombocytopenia, and multi-organ failure ​(22). Currently, there is no specific antiviral treatment for dengue infection. Management focuses on supportive care, including maintaining adequate hydration, monitoring for signs of haemorrhage, and using acetaminophen for fever and pain relief. Nonsteroidal anti-inflammatory drugs (NSAIDs) and aspirin are generally avoided due to the risk of bleeding complications​ (20).​ 

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Zika Virus (ZINV)

Zika virus, also transmitted by Aedes mosquitoes, has neurotropic properties and is capable of crossing the placental and blood-brain barriers. The ZIKV NS1 protein plays a role in immune evasion by disrupting complement activation. The virus preferentially infects neural progenitor cells, leading to microcephaly, neuronal apoptosis, and developmental delays in foetuses ​(23). In adults, ZIKV infection has been linked to Guillain-Barré syndrome, a post-viral autoimmune neuropathy ​(24). There is no specific antiviral therapy for Zika virus infection. Treatment is primarily supportive, addressing symptoms such as fever, rash, and arthralgia with rest, fluids, and analgesics like acetaminophen. Aspirin and NSAIDs are typically avoided until dengue co-infection is ruled out, due to its potential risk of haemorrhage ​(25). 

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Ebola Virus (EBOV) 

Ebola virus (EBOV) is a highly lethal filovirus responsible for severe haemorrhagic fever outbreaks. EBOV enters host cells via macropinocytosis and replicates in monocytes, dendritic cells, and endothelial cells, inducing vascular leakage, coagulopathy, and multi-organ failure​ (26). The VP35 and VP40 proteins play essential roles in immune suppression and viral assembly, while the glycoprotein (GP) mediates endothelial dysfunction, contributing to shock and mortality ​(27). Management of Ebola primarily involves supportive care, including fluid resuscitation, electrolyte management, and treatment of secondary infections. Recent clinical trials have evaluated investigational therapies, such as monoclonal antibodies and antiviral agents. For instance, a randomized controlled trial conducted in the Democratic Republic of Congo assessed the efficacy of four investigational therapies for Ebola​ (28).