The present experimental study was conducted from July 2015 to October 2016 in the Department of Anatomy, King George’s Medical University, Lucknow, Uttar Pradesh. Approval from Institutional Animal Ethical Committee was taken prior to the start of the study (Approval no. 68/IAEC/2015, dated 23/11/15).

Inclusion criteria: Total 12 male albino wistar rats, aged 1-2 months weight 100-150 grams were included in study and randomly divided into two groups.

Exclusion criteria: Female rats were excluded due to cyclic hormonal changes.

After being transferred from their colonies to the Institutional Animal House, rats were kept in a temperature-controlled environment. The baseline weight of each rat was recorded on the day of procurement. Animals were acclimatised for two weeks. Weight of each rat was also recorded during first and second week of acclimatisation. Later the rats were divided into groups and housed in marked polyethylene cages under good hygienic conditions. Twelve hours light and dark cycle and temperature was maintained. Animals were fed on standard pellet diet (5 gms/rat) and water was given ad libitum according to Committee for the Purpose of Control and Supervision of Experiment on Animals (CPCSEA) guidelines [9]. Daily intake of food and water was recorded.

Group I (Control): Total six rats which were kept without any exposure of fumes, served as control population.

Group II (Experimental): Total six rats, given eight hours daily exposure of LMRV via whole body exposure, for six days in a week for a total of 12 weeks.

In the beginning of 3^rd week, rats of group II were exposed to LMRV via whole body inhalation route. For this purpose the exposure groups were kept in a properly ventilated room. After removing the cap of liquid vaporiser bottle (containing Transfluthrin: 0.88% w/w) was inserted into the Electronic Mosquito Destroyer machine. The machine was switched on daily in the morning for 8 hours exposure from 8:00 AM to 4:00 PM, six days in a week for a period of 12 weeks. Group I (Control) animals were kept under identical conditions without exposure to liquid vaporisers. Weight of each rat was recorded weekly and tabulated.

The present study has followed standard criteria for realistic room condition for exposure considering the following information provided by Achmadi UF and Pauluhn J [10]. According to them, conclusion drawn in a workshop organised for standardisation of inhalational studies with regard to generation of test atmosphere, mode and duration of exposure and adequate selection of toxicological end points was that, for risk assessment of low dose and slowly releasing indoor insecticides such as mosquito vaporiser, in a rat model, subchronic inhalational of six hours per day for five days in a week for total 13 weeks administration should be considered as standard exposure.

The data was analysed using SPSS version 21.0. Independent samples t-test was used to compare between group differences. Within group comparison of change in body weight (as compared to enrolment) at different time interval was assessed by paired t-test. A p-value less than 0.05 was considered to be significant.

At baseline, the mean body weight of animals in control and exposure group was 132.38±17.34 and 136.72±15.25 gm, respectively (p=0.656). After two weeks of acclimatisation, statistically there was no significant difference among groups (p=0.456). At 12 week postexposure, the mean body weight of rats in group I was 223.05±44.76 and that of group II was 185.73±41.43 gm, respectively (p=0.165). Data are suggestive of reduced pattern of weight gain in exposed group rats. Weight gain in both the groups of rats was almost similar till 8^th postexposure week, after that from 9^th week onwards decremental trend in weight was seen in group II till the end of study [Table/Fig-1].

In the present study, subchronic exposure to pyrethroid based mosquito vaporiser fumes adversely affected the body weight of exposed group rats. Body weight of an organism reflects its overall state of metabolism and the capability to maintain its normal growth and development [11]. Weekly observations of body weight helped us to monitor the growth and development of rats. Initially body weight of rats was found to be increased till 8^th week, and there after decreasing trend was observed till the end of study which was statistically not significant but the data are suggestive of toxic effect of the pyrethroids on the rats’ physiology, especially during later weeks of exposure period. Similarly Sinha C et al., also reported an increasing trend in body weight of adult albino rats after oral beta-cyfluthrin (type II pyrethroid) administration at day 1,7,14 and 28 [12].

Sinha C et al., reported that body weight of rat pups exposed to prenatal, postnatal and perinatal inhalation of pyrethroid decreased significantly [12] but Adjrah Y et al., and Sayim F et al., observed that oral administration of cypermethrin (type II pyrethroid) for 28 days insignificantly reduced the body weight and caused diarrhoea as prominent clinical sign in the rats [13,14]. Sangha GK et al., also noticed that chronic oral administration of cypermethrin results in loose fecal pellets, hyperirritability and significantly decreased body weight as compared to control without affecting food and water intake of rats. In contrast to above finding, present study also did not observed loose fecal pellets but at the end of study, rats started taking less food towards the third month of experiment [15]. It may be due to difference in route of exposure in the present study. Fetoui H and Gdoura R, reported reduced food and water intake in lamda-cyhalothrin treated rats [16]. So, probably in present experiment reduced intake of food could be attributed as cause of reduced body weight instead of diarrhea. This difference can also be attributed to route of exposure. Loss of appetite could be the result of multiple factors. Abdel-Rahman A et al., found that Gulf War Illness Related (GWIR) chemicals caused neuronal cell death in the hypothalamus of exposed animals. Probably feeding centre is located in the hypothalamic region and damage to this could lead to loss of appetite [17].

Tentative hypothesis for weight reduction in the study may be decreased absorption or utilisation of food due to gastrointestinal disturbances caused by altered function of hydrolytic enzymes of small intestine by pyrethroid exposure. Another study reported that the oral administration of single dose of pyrethroid based pesticide resulted in significant changes in the activity of intestinal enzymes that may result in serious disturbances in the intestinal uptake consumption of the composite part of food [6]. Study conducted by Nagarjuna A and Doss PJ helps in explaining decreased absorption of food in pyrethroid exposed rats as they observed that there was hypertrophy of goblet cells, necrotic changes, infiltration and congestion in the duodenum [18].

Another cause for reduced appetite may be associated with damage to pituitary of pyrethroid exposed rats which was already mentioned in study conducted by Fan W et al., observed reduced pituitary weight in allethrin (type I pyrethroid) exposed rats and hypothesised that weight loss could have been due to reduction in growth hormone subsequent to loss of pituitary weight [19].

Similar to the present study, Hasan S and Maheshwari TP who exposed rats to prallethrin vapours 12 hours daily for 180 days did not find any significant variation in body weight [2]. Another study conducted by Kamble VS, also did not find any significant difference in mean body weight between control and exposure (8 hours exposure to allethrin inhalation for 30 days) group rats [20] but Srivastava A et al., noticed significant changes in body weight gain and food consumption in rats exposed to liquid mosquito repellent 8 hours/day for a period of 90 days [21].

Several factors may lead to decrease in weight gain in exposed group like loss of appetite, organ directed toxicities (gastrointestinal, endocrine, central nervous system) and other stressors like change of colony, and anxiety to strange environment.

The inhalation rate of the main chemical constituent was not done as the study did not use inhalational chamber.

In the present study, an attempt has been made to delineate the effect of subchronic exposure of pyrethroid based mosquito vaporiser fumes on body weight of male albino wistar rats. The exposed group of rats showed reduction of food and water intake which ultimately resulted in decreased weight as compared to control group rats. Several other factors may also be responsible for this reduced weight among the rats, and further study with prolonged period of duration is required.