8 minute read
POTENTIAL OF CITRUS FRUIT PEELS AS MOSQUITO REPELLENT IN AFRICA
Jimin Park
Introduction
Mosquito-borne diseases remain a persistent and severe public health challenge in many regions worldwide, particularly in Africa with 233 million cases in 2022, accounting for about 94 percent of cases globally. (World Health Organization, 2023) Despite many of these diseases being curable, many lives are often lost due to delays in treatment and inadequate access to medical care. (Kenya. Ministry of Health. Malaria Control, 1994) The pain and suffering caused by mosquito-borne diseases are profound, yet the gap between theoretical prevention and the reality on the ground remains stark. (White et al., 2014) Public hospitals frequently face shortages of essential therapeutic drugs, and private healthcare services are prohibitively expensive for many.(White et al., 2014) Additionally, cultural beliefs and reliance on superstitions further complicate eradication efforts.
As much as treatment being considered important, preventative medicine is also a crucial part of healthcare. My medical outreaches to Uganda and Kenya also depicted the urgent need for effective, affordable and safe mosquito repellents. While synthetic products are in use in some regions, the importance of sustainability and accessibility in the prevalent regions cannot be understated; limonene will be discussed throughout this article in order to provide evidence for its suitability as a mosquito repellent in mid-African regions.
Synthetic mosquito repellent DEET and alkyl phthalates
For more than 50 years, the synthetic compound DEET (N,N-diethyl-m-toluamide) (Fig. 1), has been the single most effective repellent for mosquito species and is the basis for many commercial repellent products on the market. (Rodriguez et al., 2015) Despite reports of severe toxic properties which can dramatically affect adults and especially young children including dermatitis, allergic reactions, neurological (seizures, coma) and cardiovascular toxicity, the risk of serious toxic effects from DEET is considered slight. Nevertheless, DEET should always be used at the lowest effective dose possible. (Ghali & Albers, 2024; Koren et al., 2003) Also, dimethyl and di-n-butyl phthalates (DMP and DBP, respectively) (Fig. 2 and Fig. 3 respectively), which are effective mosquito repellents and were widely used in the last century, are no longer generally recommended for use as repellents due to their toxicity. (Zhang et al., 2019)
Why Limonene?
Limonene is an abundant component of citrus fruit (oranges, mandarins, lemons, limes etc) especially in their peels, and have been traditionally valued for their aromatic properties in various cultures. It has recently garnered attention for its potential as a mosquito repellent.(Dutta et al., 2024)
The abundance of citrus in the targeted regions plays a big role in the choice of limonene. Citrus fruits are widely cultivated across Africa, with significant production in several regions of the continent. Countries such as South Africa, Egypt, Morocco, and Kenya are notable for their extensive citrus orchards, contributing to a substantial supply of fruits like oranges, lemons, and limes. In South Africa, citrus farming thrives in the Limpopo and Mpumalanga provinces, while Egypt and Morocco are major producers in the Mediterranean region. Kenya's coastal and central highlands also support large-scale citrus cultivation. (Fig. 4) With increased in the citrus production, agricultural wastes have become a worrying concern worldwide, so the smart ways of utilizing the citrus waste into biological applications are becoming a significant issue. (Tabisa Diniso1 & Oyedeji 2024) Furthermore, these citrus abundancy region in mid-Africa is well matched with the malaria endemic areas in sub Sahel region. (Fig. 5)(Sharp, 1999)
The abundant availability of these fruits presents a promising opportunity for sustainable mosquito control in African communities.
Effects of Limonene on the Nervous and Olfactory Systems of Mosquitoes
Citrus fruits are rich in a variety of bioactive and chemical compounds including limonene (CH) ₁₀₁₆ (Fig. 6), citral (CHO), linalool (CHO), citronellal and Aurantimaric acid. (Dhanashree K. P., et ₁₀₁₆₁₀₁₈ al., 2023; Asadollahi, et al., 2019) Limonene is a colorless liquid, aliphatic hydrocarbon classified as a cyclic monoterpene, and is particularly abundant in the peels of citrus fruits such as oranges, lemons, and limes. This compound not only contributes to the distinctive scents of these fruits but also plays a crucial role in their biological activity. (Anandakumar et al., 2021)
Its effectiveness as a mosquito repellent is a consequence of its ability to interfere with the olfactory and nervous systems of mosquitoes. Mosquitoes detect humans through olfactory and thermal cues mediated by sensory systems. The primary olfactory detection mechanism involves odorant receptors (ORs) located on the antennae and maxillary palps. Notably, the receptors OR1, OR2, and OR7 are sensitive to volatile compounds emitted by humans, such as carbon dioxide (CO), lactic acid, and ₂ various fatty acids. CO is particularly detected by the CO-sensitive receptor neuron, ionotropic ₂₂ receptor IR21a, which is highly responsive to the miniscule changes in atmospheric CO concentration ₂ that occur due to human respiration. (Olsson, et al., 2022) When mosquitoes are exposed to limonene, it disrupts and desensitizes their sensory perception which prevents them from detecting CO and ₂ other chemicals emitted by humans. Studies show that binding of limonene to ORs can alter the signaling pathways: by affecting the activation of G proteins and the production of secondary messengers like cyclic AMP (cAMP), limonene can disrupt the normal signal transduction process, impairing the ability of olfactory neurons to transmit accurate information about human odors. (Khan, et al., 2015) This effect significantly reduces the likelihood of mosquito locating and biting the hosts, thereby reducing the incidences of mosquito-borne diseases.
Additionally, mosquitoes utilize thermal cues detected by thermoreceptors such as TRPA1 (Transient Receptor Potential Ankyrin 1), which are sensitive to body heat and infrared radiation. These receptors allow mosquitoes to sense the warmth of a human body from a distance, further aiding in host localization. As shown, studies demonstrate that limonene can affect mosquito's nervous system and alter their feeding behavior, further enhancing its repellent properties.(Bohbot, 2022; McCall & Eaton, 2001; Nematollahi et al., 2021)
References
Anandakumar, P., Kamaraj, S., & Vanitha, M. K. (2021). D-limonene: A multifunctional compound with potent therapeutic effects. J Food Biochem, 45(1), e13566. https://doi.org/10.1111/jfbc.13566
Asadollahi, A., Khoobdel, M., Zahraei-Ramazani, A. et al. (2019). Effectiveness of plant-based repellents against different Anopheles species: a systematic review. Malar J 18, 436. https://doi.org/10.1186/s12936-019-3064-8
Bohbot, D. M. R. J. D. (2022). Sensory ecology of disease vectors, Chapter 3: The molecular and neural determinants of olfactory behaviour in mosquitoes (C. R. L. R. Ignell, M.G. Lorenzo and S.R. Hill, Ed.). https://doi.org/10.3920/978-90-8686-932-9 https://www.academia.edu/115988191/Preparation_of_Mosquito_Repellent_Dhoop_from_ Orange_Peels?sm=b
Dhanashree K. P., Vaibhav V. D., Ankit C. R., Vaishnavi S. C. (2023). Preparation of Mosquito Repellent Dhoop from Orange Peels. International Journal for Multidisciplinary Research, 5(2), IJFMR23022694.
Dutta, R. S., Sahu, S., Baishya, R., Pachuau, L., Kakoti, B. B., & Mazumder, B. (2024). Essential oils extracted from Citrus macroptera and Homalomena aromatica (Spreng.) Schott. exhibit repellent activities against Aedes aegypti (Diptera: Culicidae). J Vector Borne Dis, 61(1), 107116. https://doi.org/10.4103/0972-9062.392256
Ghali, H., & Albers, S. E. (2024). An updated review on the safety of N, N-diethyl-meta-toluamide insect repellent use in children and the efficacy of natural alternatives. Pediatr Dermatol, 41(3), 403-409. https://doi.org/10.1111/pde.15531
Kenya. Ministry of Health. Malaria Control, P. (1994). Epidemiology of malaria in Kenya. Afr J Med Pract, 1(1), 5-6. https://www.ncbi.nlm.nih.gov/pubmed/12287810
Khan, H. A., & Hassan, M. M. (2015). "Limonene as a Natural Mosquito Repellent: A Review." Journal of Vector Borne Diseases, 52(2), 123-130.
Koren, G., Matsui, D., & Bailey, B. (2003). DEET-based insect repellents: safety implications for children and pregnant and lactating women. CMAJ, 169(3), 209-212. https://www.ncbi.nlm.nih.gov/pubmed/12900480
McCall, P. J., & Eaton, G. (2001). Olfactory memory in the mosquito Culex quinquefasciatus. Med Vet Entomol, 15(2), 197-203. https://doi.org/10.1046/j.0269-283x.2001.00304.x
Nematollahi, N., Ross, P. A., Hoffmann, A. A., Kolev, S. D., & Steinemann, A. (2021). Limonene Emissions: Do Different Types Have Different Biological Effects? Int J Environ Res Public Health, 18(19). https://doi.org/10.3390/ijerph181910505
Laura A., Beatriz G., et al. (2023). World Malaria Report 2023. World Health Organization. 18. https://www.who.int/teams/global-malaria-programme/reports/world-malaria-report-2023
Olsson, S. B., & Söderlund, J. (2022). "Mosquito Olfaction and Host Detection: The Role of Odorant and Thermoreceptors." Journal of Experimental Biology, 225(11), jeb243560. DOI: 10.1242/jeb.243560.
Rodriguez, S. D., Drake, L. L., Price, D. P., Hammond, J. I., & Hansen, I. A. (2015). The Efficacy of Some Commercially Available Insect Repellents for Aedes aegypti (Diptera: Culicidae) and Aedes albopictus (Diptera: Culicidae). J Insect Sci, 15(1), 140. https://doi.org/10.1093/jisesa/iev125
Sharp, J. C. M. C. D. L. S. B. (1999). MAPPING MALARIA RISK IN THE HIGHLANDS OF AFRICA. Tabisa Diniso1, A. O. O., Jerry O. Adeyemi , Gugulethu M. Miya , Yiseyon S. Hosu , Opeoluwa O., & Oyedeji , S. K. K., Adebola O. Oyedeji. (2024). Citrus wastes: A valuable raw material for biological applications. Journal of Applied Pharmaceutical Science, 14(08), 011-026. https://doi.org/0.7324/JAPS.2024.158781
White, N. J., Pukrittayakamee, S., Hien, T. T., Faiz, M. A., Mokuolu, O. A., & Dondorp, A. M. (2014). Malaria. Lancet, 383(9918), 723-735. https://doi.org/10.1016/S0140-6736(13)60024-0
Zhang, Q., Chen, X. Z., Huang, X., Wang, M., & Wu, J. (2019). The association between prenatal exposure to phthalates and cognition and neurobehavior of children-evidence from birth cohorts. Neurotoxicology, 73, 199-212. https://doi.org/10.1016/j.neuro.2019.04.007
