Another ‘bug hunter’ paper published in Parasites and Vectors piqued my interest in Malaria World this week. Abas et al captured 20,449 mosquitos between June and December 2023 for ‘Risk of Aedes-borne diseases in and around the Tanzanian seaport of Tanga despite community members being more concerned about malaria’. Most of these (94.9%) were Culex quinquefasciatus or Mansonia uniformis, species not blamed for spreading disease. Only 19 (<0.1%) were Anopheles, the supposed Malaria vector. So the study decided to focus on Aedes Aegypti, 5.1% of the mosquitos captured, that has been blamed for spreading Dengue and Chikungunya. And among other great contributions to science they found that Aedes Aegypti are susceptible to bendiocarb and DDT, and resistant to permethrin. Can you believe they are still using DDT?
What is Chikungunya? It is not a major concern to the 236 residents of the port of Tanga surveyed that was part of the study. A majority 64.8% know mosquitos are blamed for spreading Malaria, 26.3% know about Dengue, but just 1.7% are aware of Chikungunya.
And I must confess, until I read this paper I knew nothing about it. The WHO fact sheet which states that Chikungunya is a disease transmitted to humans by Aedes mosquitos in Africa, Asia, and the Americas. It is similar to Dengue and Zika and so is easy to misdiagnose. Chikungunya causes fever and severe joint pain, which is often debilitating and varies in duration; other symptoms include joint swelling, muscle pain, headache, nausea, fatigue and rash (see picture). Severe symptoms and deaths from chikungunya are rare and usually related to other coexisting health problems.
Of course there is no link to any evidence blaming Aedes mosquitos. In a New England Journal review article by Weaver and Lecuit (2015) there is a reference to Ross (1955) The Newala Epidemic published in the Journal of Hygiene about the isolation of a virus blamed for the outbreak of the of disease, known locally as ‘Chikungunya’, in the Newala district of Tanganyika. The virus was supposedly isolated from human patients and inoculated into mice. Aedes aegypti were allowed to feed on patients but none transmitted the illness to baby mice that they bit later.
However, the authors linked a supposed virus to the illness and found it in a mosquito and concluded The evidence linking the virus isolated to the human disease is very strong. However, there is no evidence of transmission of the disease to humans by mosquito bites.
I have no intention of delving too deep into the virology of this paper. Someone more expert than I can do that. However, it is very clear to me that Koch’s postulates were not met. I suspect that the instinct of the vast majority of residents of Tanga is correct. They don’t need to worry about mosquitos spreading a condition called Chikungunya.