Toxic effects of mosquito coil (a mosquito repellent) smoke on rats. II. Morphological changes of the respiratory system

Systematic review of clinical manifestations, management and outcome following accidental ingestion of liquid mosquito repellent vaporiser in children

BACKGROUND

Pyrethroid-based mosquito repellents are widely used to control mosquito-borne diseases. Liquid mosquito-repellent vaporisers are effective modes of pyrethroid delivery but can also pose significant health risks if ingested or used improperly.

OBJECTIVE

This systematic review was performed to assess the demographic distribution, clinical presentation, management strategies and outcomes in children resulting from accidental ingestion of liquid mosquito repellent vaporiser.

METHODS

The study adheres to the reporting standards outlined in the PRISMA Statement for Systematic Reviews and was prospectively registered with PROSPERO (record # CRD42023413937) to enhance transparency and minimise reporting bias. A comprehensive search was conducted on PubMed, Scopus and Google Scholar using specific MeSH terms related to insecticides, mosquito repellents, pyrethroids, ingestion, poisoning, toxicity and prevention. The reference lists of the included studies were also reviewed for additional relevant articles. The inclusion criteria involved studies published in peer-reviewed journals between 2000 and 2023 that focused on children under 18 years old with a history of mosquito-repellent ingestion based on primary data.

RESULTS

Twelve studies met the inclusion criteria; these were primarily case reports from India, China and the UAE. Male children were predominantly affected, and symptoms included vomiting, convulsions, cough and respiratory distress. Management primarily involved supportive and symptomatic measures, including atropine for salivation and antiepileptic drugs for seizures. Respiratory support was provided for respiratory complications.

CONCLUSION

Despite the known risks and diverse presentations of pyrethroid poisoning caused by liquid mosquito repellent vaporiser in children, the limited substantial evidence in the literature underscores the urgent need for comprehensive research to refine management approaches and enhance preventive measures.

Exposure to mosquito coil smoke may be a risk factor for lung cancer in Taiwan

Background

About 50% of lung cancer deaths in Taiwan are not related to cigarette smoking. Environmental exposure may play a role in lung cancer risk. Taiwanese households frequently burn mosquito coil at home to repel mosquitoes. The aim of this hospital-based case-control study was to determine whether exposure to mosquito coil smoke is a risk for lung cancer.

Methods

Questionnaires were administered to 147 primary lung cancer patients and 400 potential controls to ascertain demographic data, occupation, lifestyle data, indoor environmental exposures (including habits of cigarette smoking, cooking methods, incense burning at home, and exposure to mosquito coil smoke ), as well as family history of cancer and detailed medical history.

Results

Mosquito coil smoke exposure was more frequent in lung cancer patients than controls (38.1% vs.17.8%; p<0.01). Risk of lung cancer was significantly higher in frequent burners of mosquito coils (more than 3 times [days] per week) than nonburners (adjusted odds ratio = 3.78; 95% confidence interval: 1.55-6.90). Those who seldom burned mosquito coils (less than 3 times per week) also had a significantly higher risk of lung cancer (adjusted odds ratio = 2.67; 95% confidence interval: 1.60-4.50).

Conclusion

Exposure to mosquito coil smoke may be a risk factor for development of lung cancer.

Mosquito coil smoke inhalation toxicity. Part II: subchronic nose-only inhalation study in rats

This paper addresses the results of a subchronic inhalation study in rats exposed to the smoke of burning mosquito coils manufactured in Indonesia. The objective of the study was a comparative assessment of different mosquito coils, including a blank coil, utilizing the OECD No. 413 testing paradigm, however, with the focus on hazard identification at a single maximum tolerated exposure concentration rather than concentration-response. Groups of rats were nose-only exposed 6 h a day, 5 days a week for 13 weeks to an average particulate concentration of 30 mg m(-3) from either blank coils or coils that contain the insecticidal ingredient transfluthrin. Nose-only air-exposed rats served as a control. A range of markers of exposure have been characterized to define the most critical exposure metrics with regard to total suspended particulate matter (TSP) and potentially noxious volatile products of combustion. During the course of the exposure period the smoke-exposed rats showed clinical signs suggestive of acute upper respiratory tract sensory irritation. Body weights were mildly affected in the male rats, but food and water consumption were indistinguishable amongst the groups. Carboxyhemoglobin concentrations were approximately 11% throughout the exposure period in smoke exposed rats. Hematology, clinical pathology and urinalysis as well as the analysis of organ weights and histopathology of extrapulmonary organs and the lung did not reveal any evidence of adverse systemic or local effects, whereas in the anterior region of the nasal passages, and to some extent also in the larynx, irritant-related changes typical for water-soluble upper respiratory irritants were found. Markers of pulmonary inflammation or increased phagocytosis and lysosomal activity in bronchoalveolar lavage were indistinguishable amongst the groups. gamma-Glutamyltranspeptidase was significantly increased in the smoke exposure groups, which is taken as indirect evidence of an adaptive upregulation of the pulmonary antioxidant glutathione. In rats exposed to mosquito coil smoke containing transfluthrin, a somewhat increased frequency of alveolar macrophages with foamy appearance was identified through cytodifferentiation but not histopathology compared with the blank coil. From the specific staining of intracellular phospholipids, the notion is supported that this equivocal finding is probably related to an increased uptake of modified pulmonary surfactant rather than increased engulfment of insoluble particulate matter since pigmentation or clustering or intra-alveolar cells did not occur. The results of this subchronic inhalation study support the conclusion that smoke from burning mosquito coils in concentrations high enough to elicit acute upper respiratory tract irritation due to the presence of common wood-combustion products (such as aliphatic aldehydes) did not cause any adverse effect in the lower respiratory tract or any other extrapulmonary organ. The most critical mode of action is related to acute and readily perceivable sensory irritation. The concentration tested was estimated to be well above that occurring under more realistic exposure conditions. Therefore, overnight exposure to the smoke from burning mosquito coils (manufactured in Indonesia) is unlikely to be associated with any unreasonable health risk.

Behavioral and neurochemical effects induced by pyrethroid-based mosquito repellent exposure in rat offsprings during prenatal and early postnatal period

Synthetic pyrethroids, besides their use in agriculture, are prevalently used in our houses as mosquito repellent (MR) in the form of aerosol, mats, coils and liquid vaporizers. Inhalation of fumes of the MR/liquid vaporizers may get entry into the brain by breaching the developing blood-brain barrier, hence deleterious to developing nervous system and can lead to long-term functional deficits. In the present study the consequence of MR exposure has further been investigated at various stages of development, evaluating free radical mediated effect pertinent to neurobehavioral and neurochemical functioning. Rat pups were exposed to pyrethroid-based MR (allethrin 3.6% w/v, 8 h/day through inhalation) during prenatal (GD1-20), postnatal (PND1-30) and perinatal (GD1-PND30) period of development and assessments were made on PND31. We observed significant oxidative stress, where an increase in lipid peroxidation and a decrease in antioxidants, glutathione, superoxide dismutase and catalase in various brain areas (cerebellum, corpus striatum, frontal cortex and hippocampus) were evident at all the exposure schedules. The hippocampus was the most affected region and further exhibited altered cholinergic functioning in the form of significant decrease in cholinergic (muscarinic) receptor binding (prenatal 32%, postnatal 35%, perinatal 38%) and inhibition in acetylcholinesterase activity (prenatal 20%, postnatal 31% and perinatal 33%). The neurochemical changes were found to accompany decrease in learning and memory performance in exposed rats, the function governed by hippocampus. The result suggests that pyrethroid-based MR inhalation during early developmental period may have adverse effect on developing nervous system causing cholinergic dysfunction leading to learning and memory deficit.

Personal protection against mosquitoes in Dar es Salaam, Tanzania, by using a kerosene oil lamp to vaporize transfluthrin

The effectiveness of a cheap and easy method of household protection against Culex quinquefasciatus Say and other mosquitoes (Diptera: Culicidae) was investigated in Dar es Salaam, Tanzania. Kerosene-burning lamps (korobois) were modified to heat and vaporize transfluthrin, a volatile pyrethroid insecticide. When transfluthrin was added to fuel of the lamp, protection against biting was poor unless a very high concentration of insecticide was used. A modified lamp (= vaporizing koroboi) was designed to overcome this problem by mixing the insecticide with vegetable oil and heating it to 120 degrees C in a tin held just above the flame. The concentration of 0.1% transfluthrin in vegetable oil gave 50-75% reduction in biting, a similar degree of protection to that obtained from burning a mosquito coil containing a synthetic pyrethroid (0.25% d-allethrin) and significantly better protection than a locally bought coil (brand 'White Crane', probably containing DDT). Greater protection (consistently > 90%) was achieved with a higher concentration of transfluthrin (0.5%) in the vegetable oil. This modified lamp is simple, cheap and employs locally available technology. With further development, and due regard to inhalation toxicity of the vaporized materials, it may offer a more cost-effective alternative to a mosquito coil as a means of personal protection, and a useful complement to a net for the early part of the evening before bedtime.

Aliphatic aldehydes and allethrin in mosquito-coil smoke

Presence of aliphatic aldehydes and allethrin in the smoke produced by two brands of mosquito-coil was determined by high performance liquid chromatography. It was observed that burning mosquito-coil produces a greater amount of formaldehyde, acetaldehyde and acrolein in the gaseous phase, whereas lesser amount of particulate-bounded aldehydes. Aldehydes bounded in particulates were, however, enriched in terms of concentration. Allethrin was found to occur only in particulates of 0.1-1.0 micron size. The results reveal that allethrin may not be capable of attacking the mosquitoes effectively.

Morphological changes in the respiratory system of mice after inhalation of mosquito-coil smoke

Male ICR mice were exposed to mosquito-coil smoke with d-allethrin or without d-allethrin at airborne particles concentration of 1.27 mg/m3, 7 h/day, 7 days/week for 1, 3, 6, and 12 months. Additional groups of air exposure animals served as controls. At 1 month after exposure, the histopathological lesions included the loss of cilia, and the alteration of the alveolar pattern in the treated and the sham mice. Volume fractions of the type I and II cells were smaller (0.028 +/- 0.006, 0.044 +/- 0.002) in the treated group than those of the controls (0.049 +/- 0.008, 0.059 +/- 0.003). Fractions of the lumina of vessels and the vessel wall decreased in both the treated and the sham groups as compared to the control group. However, the volume fraction of alveolar air space increased significantly in both treated and sham groups as compared to the controls (0.619 +/- 0.022, 0.685 +/- 0.018 vs. 0.507 +/- 0.025). After 3- and 6-months exposure, the lesions observed in the trachea persisted. The intercellular fibrosis in the lung was increased in both the treated and sham groups at 6 months and became more severe at the later stages. At 12-months exposure, an increase in vascularity of the alveolar wall was observed and fine granular debris was frequently present in the alveolar space. The fraction volumes of the type II cells in the treated group and the type I cells in the sham group were significantly increased (0.059 +/- 0.010, 0.042 +/- 0.003) compared with those of the controls (0.038 +/- 0.008, 0.033 +/- 0.003). However, the fraction volume of air space and vessel lumen were not different among the three groups. Finally, there were no differences in the morphologic appearance of the airways and the lung periphery between the treated and the sham-exposed animals.

Biochemical and cellular changes in bronchoalveolar lavaged samples from rats after inhalation of mosquito-coil smoke

A group of 30 female albino rats were exposed to mosquito-coil smoke, 8 hours a day, 6 days per week, for 6 months. Another group which was exposed to air served as control. At the end of the experiment, the enzyme activities, total protein and lecithin contents as well as cellular responses in the lung lavage between the control and smoke-exposed rats were compared. Morphological observations using scanning and transmission electron microscopy demonstrated that the alveolar macrophages of smoke-exposed rats lost their typical ruffled membranes. They possessed small cytoplasmic processes on their smooth cell surfaces, small particles in phagolysosomes and mitochondria with a very electron-dense matrix. The levels of total protein and lecithin and the activities of lactate dehydrogenase, acid phosphatase and beta-glucuronidase in the lung-lavage fluid of smoke-exposed rats were significantly (P less than 0.05) higher than those of the controls. Increases (P less than 0.05) of serum enzymes, including lactate dehydrogenase, aspartate aminotransferase, isocitrate dehydrogenase and aldolase, indicated damage of liver tissues, but the levels of serum urea and urea nitrogen remained at the control levels implying normal functions of the kidneys of the mosquito-coil smoke-exposed rats. The level of serum tri-iodothyronine also increased significantly (P less than 0.05), but thyroxine remained at the control level.