Seasonal Prevalence and Impact of Environmental Variables in Emergence of Aedes Mosquito in Multan, Pakistan

Faheem Ali* and Amjad Farooq

Institute of Zoology, Bahauddin Zakariya University, Multan, Punjab, Pakistan.

ABSTRACT

Mosquito borne infection is considered a most important public health problem all over the world including the dengue virus. The dominant occurrence of Aedes mosquitoes under the influence of environmental factors (temperature, relative humidity, and rainfall) of Multan city was assessed during 2014-2016. In this study, Aedes larvae were collected by using the entomological dipping method and identified in the laboratory. The results showed mean (±SD) temperature, rainfall, and relative humidity during 2014-2016 ranged 12.88-35.43oC, -0.33-87.43mm, and 36.17-72.17%, respectively. Likewise, maximum Aedes larvae were found during the month of November, with 348.67 Aedes larvae from indoor while 71.67 from outdoor. The emergence of Aedes larvae was found after rainy season while decline trend was observed at non-rainy, extreme temperatures and relative humidity conditions. This study could be used in further studies in order to evaluate Aedes mosquito emergence in relation with different environmental variables, and to establish integrated vector control strategies in the future.

Article Information

The article was presented in 42nd Pakistan Congress of Zoology (International) held on 23-25th April 2024, organized by University of Azad Jammu & Kashmir, Muzaffarabad, Pakistan.

Authors’ Contribution

AF conceived and designed the study. FA performed research, provided reagents and materials; and drafted the manuscript. Both authors revised and approved the manuscript.

Key words

Aedes, Temperature, Rain fall, Relative humidity

DOI: https://dx.doi.org/10.17582/ppcz/42.59.64

* Corresponding author: [email protected]

1013-3461/2024/0059 $ 9.00/0

Copyright 2024 by the authors. Licensee Zoological Society of Pakistan.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

INTRODUCTION

Dengue fever is a well-known viral infection, influenced by many environmental factors (Mahmud et al., 2019) that infect human and threatened 975 million peoples around the world specifically in tropically and sub-tropically areas of South-Eastern Asia, America and the Pacific region (Haider and Iqbal, 2016). Although, dengue virus belonged to family flaviridae which has 4 strains or serotypes that are serologically similar but different by genetically (Zanotto et al., 1996). Additionally, Aedes aegypti and Aedes albopictus are the mosquito vectors that are responsible for the transmission of the dengue virus in human causing symptoms such as high grade fever, painful muscles and joints, vomiting, nausea, skin rashes, severe headache, and pain behind the eyes (Manzoor et al., 2015; Habib et al., 2016). Aedes mosquito is primarily responsible for the spread of dengue in all regions of the world (Manzoor et al., 2015) while later is usually thought to be a weak with minor epidemics (Kim-Lien et al., 2015).

The Aedes population has a major effect on the human populations as its life cycle is closely related with the human activities (Madzlan et al., 2016) and can adopt different habitats such as aegypti occupied urban residences however albopictus invade rural, sub-urban and urban environmental conditions (Kim-Lien et al., 2015). Aedes aegypti established itself in the urban areas and lesser extent to semi-urban area but is not established in the rural area. On the other side, Aedes albopictus population had established itself in rural areas rather than urban areas. Moreover, for breeding, Aedes aegypti preferred indoor and Aedes albopictus preferred both indoor and outdoor (Herath et al., 2022). 

Aedes is not only adopt the local domestic environments but can also adopt demographic growth and migrate through human (Carneiro et al., 2017). In tropical and sub-tropical lands of Asia, this viral infection is mostly spread by Aedes aegypti and Aedes albopictus and existed in the surroundings of human. On the other hand, Aedes albopictus is originate in sub-tropical zones than Aedes aegypti due to its tolerance to low temperature. Additionally, extreme invasion of dengue infestation is related with the adult vectors under the ideal setting of humidity and temperature in rainy seasons (Carneiro et al., 2017).

Moreover, Aedes mosquito required clean watery environment during initial three developmental stages i.e., egg, larvae and pupae both in natural and artificial conditions (Madzlan et al., 2016), depends upon water temperature and its environmental conditions (Gubler, 1997). Furthermore, mosquitos completed their three developmental stages (egg to adult mosquito) in 7-10 days. The female Aedes mosquito lays its eggs in potential water containers (CDC, 2019) where eggs are fastened with the walls of container and could survive up to 8 months. Eggs hatched within a few days to months-long duration when enclosed with water till emergence of larvae in water container and later converted into pupae in next 5 days. In next 2–3 days pupae develop into mature mosquito (CDC, 2019).

After the onset of the monsoon, dengue virus infestations occurred as a burning health issue due to higher arrival of Aedes mosquito in Pakistan (Manzoor et al., 2015). Due to greater suitable vector environment and habitats, dengue virus has occupied in many regions in Pakistan in last decade. This disease victimized mainly the adult population of human in Pakistan as well as all over the world (Naqvi et al., 2015). Present study was planned to evaluate the impact of different environmental variables such as rainfall, relative humidity, and temperature in the emergence of Aedes mosquito responsible for the infestation of dengue fever in district Multan, Punjab; Pakistan. Moreover, this study will be also helpful in future to control the dengue virus epidemics by earlier prediction by evaluating the impact of environmental variables that favored vector emergence in any region of the world.

Aim of the study was to evaluate the seasonal prevalence of Aedes mosquito and impact of environmental variables upon Aedes mosquito emergence in Multan, Pakistan during the year 2014-2016.

MATERIALS AND METHODS

Growth conditions

Previously it is demonstrated that the Aedes can adapt different habitats with human migration (Kim-Lien et al., 2015; Carneiro et al., 2017) as adapted different habitats of Multan. Multan is located at southern area of Punjab; Pakistan. Its climate is arid that usually experienced hot summer with higher temperature and cold winters with lowest temperature.

To determine the effect of arid climate of Multan in the emergence of Aedes, the vector larvae were collected from the natural environment of inside (Indoor) and outside (Outdoor) of the houses. During Aedes larvae sampling, temperature was recorded in Celsius degrees by using ordinary thermometer while relative humidity was measured in percentage by using wet and dry bulb thermometers and rainfall was measured in millimeters by using ordinary rain gauge.

Sample collection

Larvae were collected at different stages of its lifecycle from different natural water containers and stagnant water ponds via dipping method (Robert et al., 2002) by utilizing collection tools i.e., sampling scoop, transparent glass jar, magnifying glass, torch and strainer.

The wild urban populations of Aedes larvae were sampled randomly during the day times from two premises. In 1st premises (indoor sites), aqueous habitats of inside of houses which were considered for larvae sampling i.e., water containers used by human in washing and drinking, animal’s drinking pots, room water coolers, main whole covers, used/spare tires, air condition water collection containers, leaking water taps, flower jars, house stagnant water, household rubbishes, roof top junks, refrigerator trays, garbage, and construction rubbish. Whereas, in 2nd premises (outdoor sites) aqueous habitats of outside of houses which were considered i.e., park shrubberies, tyres, street and road side trash, flower pots, leaked water taps, air coolers, open manholes/drains, water vessels used for puncture in the shops, sanitation wastes in buildings, park and tree holes, construction wastes, bird pots, air conditioner outlets, water tanks, fountains and stagnant water at roadside.

The Aedes larvae were collected during the year 2014-2016 with different month’s interval at different temperature, average rainfall, and relative humidity (Table I). The collected Aedes larvae were taken to the laboratory and were identified by using standard taxonomic keys as prescribed previously (Darsie and Pradhan, 1990; Tyagi et al., 2015) with little modifications.

 

Table I. Mean values of metrological parameters and total Aedes larvae found in Multan Pakistan during the year 2014-2016.

Months	Climate			Aedes larvae (Vector)
	Average temperature (oC)	Average rain fall (mm)	Average relative humidity (%)	Indoor	Outdoor	Total
January	12.88	1.63	72.17	8.33	0.00	8.33
February	16.55	10.60	64.67	7.33	1.33	8.67
March	21.10	47.17	63.17	41.67	10.67	52.33
April	27.98	14.17	44.00	83.00	12.67	95.67
May	33.35	27.00	36.17	59.67	9.33	69.00
June	35.43	16.83	42.83	12.33	2.00	14.33
July	33.62	87.43	60.50	52.00	6.67	58.67
August	32.62	60.80	62.67	134.67	32.00	166.67
September	31.47	5.27	59.67	188.00	37.00	225.00
October	27.68	11.23	56.00	257.67	53.00	310.67
November	20.62	0.07	61.00	348.67	71.67	420.33
December	15.32	-0.33	69.83	125.33	14.33	139.67

 

Statistical analysis

To analyze the emergence of Aedes larvae, variance analysis was performed. Temperature, average rainfall, and relative humidity were recorded daily in three repeats and average value was calculated for a month although error bars represent the average ± SD of recorded values.

Correlation among total Aedes larvae and numerous metrological parameters were performed by using regression analysis in MS Excel. Asterisks over the values indicate a significance level among mean values of metrological parameters and total Aedes larvae was evaluated via regression analysis (*P ˂ 0.05, **P ˂ 0.01, ***P ˂ 0.001).

RESULTS

Multan climate is hot and arid that favored Aedes mosquito breeding and its emergence in September, October and November. Consequently, the rainfall, relative humidity, and temperature were recorded in 2014-2016 (Table I). The maximum temperatures 35.43°C were recorded in June, while minimum values were recorded as 12.88°C in January during 2014 to 2016. Recorded data showed maximum rainfall 87.43 mm in July while maximum relative humidity was recorded (72.77%) in January during three consecutive years (2014-2016). Moreover, the mean prevalence of Aedes larvae were found highest in the month of November (348.67 from indoor and 71.67 from outdoor) while the lowest in January (8.33 from indoor and 0.00 from outdoor), showing that Aedes had the preference for indoor breeding, as described in Table I. Collectively, the maximum Aedes larvae (603 and 766) were collected in November, 2015 and October, 2016 when temperature, rainfall and relative humidity were found favorable for its breeding and development. Prevalence of Aedes (Dengue Vector) larvae in District Multan during years 2014-2016 is represented in Table II, indicating no significant difference between the prevalence of indoor and outdoor Aedes larvae. Table III shows the prevalence of Aedes (Dengue vector) larvae in District Multan during years 2014-2016.

 

Table II. Prevalence of Aedes (Dengue Vector) larvae in District Multan during years 2014-2016.

Year	Aedes (Indoor)	Aedes (Outdoor)
2014	0.0000 A	0.2500 A
2015	0.5833 A	0.1667 A
2016	0.0833 A	0.2500 A

 

Means bearing different letters are significantly different from each other.

 

Table III. Prevalence of Aedes (Dengue Vector) larvae in District Multan during years 2014-2016.

Month	Aedes (Indoor)	Aedes (Outdoor)
January	0.0000 A	0.0000 A
February	0.0000 A	0.0000 A
March	0.0000 A	0.0000 A
April	1.6667 A	0.0000 A
May	0.3333 A	0.0000 A
June	0.0000 A	0.0000 A
July	0.6667 A	0.0000 A
August	0.0000 A	0.3333 A
September	0.0000 A	1.3333 A
October	0.0000 A	0.3333 A
November	0.0000 A	0.6667 A
December	0.0000 A	0.0000 A

 

Means bearing different letters are significantly different from each other.

 

Regression analysis (r value) was performed to determine the co-efficiency among different metrological parameters and Aedes larvae in Multan (Table IV). Findings of regression analysis provided that total larvae showed significant (P<0.001) correlation with indoor and outdoor larvae, but insignificant (P>0.05) correlation with relative humidity, temperature and rain fall. However, temperature significantly affected the relative humidity (P<0.001) and rainfall (P<0.05).

 

Table IV. Relationship among different metrological parameters and Aedes larvae found in Multan Pakistan during 2014-2016.

Parameters	Indoor larvae	Outdoor larvae	Total larvae	Relative humidity	Temperature	Rain fall
Indoor larvae	1
Outdoor larvae	0.916***	1
Total larvae	0.998***	0.940***	1
Relative humidity	0.014NS	0.017NS	0.015NS	1
Temperature	0.063NS	0.074NS	0.065NS	0.690***	1
Rain fall	0.200NS	0.149NS	0.194NS	0.064NS	0.369*	1

 

***P<0.001, *P<0.05, NSP>0.05.

 

 

Additionally, the dependent of temperature on the emergence of total number of Aedes larvae during the studied years (2014-2016) is shown in Figure 1A. Extremely high and low temperature suppressed the breeding and growth of the Aedes larvae. At extremely low temperature (0-18oC) from January to February and high temperature (32-36oC) in May to July, no or less Aedes larvae were observed. However, during September to November when temperature ranged from 20-30oC, maximum larvae were found.

Furthermore, the role of rainfall in the emergence of Aedes larvae was also examined by measuring average rainfall and collecting total number of larvae (outdoor and indoor) after different month’s interval in 2014 and 2016. Rainfall established water holdings and provide environment for female Aedes mosquito to lay its ova and then developed into larvae. Higher rainfall in July, 2015 and August 2016 gave ultimately larvae emergence during August to November with maximum larvae population in October, 2015 and November, 2016 (Fig. 1B). Hence, the results showed positive relationship between rainfall and larvae incidences.

Relationship between number of Aedes larvae and relative humidity was also plotted as Figure 1C, which showed peak of Aedes larvae incidences at 50 to 65%. Relative humidity in the atmosphere due to higher rainfall in July, 2015 and August 2016 gave favorable environment for maximum emergence of larvae during August to November 2015 and October 2016. Collectively, these results showed the positive roles of moderate temperature, rainfall and relative humidity in the emergence of larvae suggested and confirmed the important roles of these environmental factors in the hatching and breeding of Aedes larvae which in turn caused dengue epidemic in Multan in late 2015.

DISCUSSION

Dengue is usually considered to be an urban disease and its infestations are increasing because it is caused by the species of the Aedes mosquito (Aedes aegypti and Aedes albopictus). The incidence of dengue vectors to new geographical areas, its climate, concentration of population, household water and trash storage to recycle the waste materials can serve as risk factors for dengue virus infections (Madzlan et al., 2016).

In this study, Aedes larvae were found higher from inside of the houses than outside of the houses of Multan during 2014-2016. These findings are in general agreement with that of reported by Herath et al. (2022), who have documented that Aedes was found moderately in the urban area and to a lesser extent in semiurban but not in the rural area and Aedes mostly preferred indoor breeding. 

The higher number of Aedes larvae were collected in November, 2015 and October, 2016. The same findings were reflected by Sarwar and Rasool (2022) that revealed the highest breeding of Aedes albopictus from Faisalabad district during 2019-2020 in the months of September-November and previously by Asrar et al. (2017) whom found Aedes prevalence in Multan city, during February-March and later in July, September and maximum in November.

Although temperature has great impact on mosquitoes growth because mosquitoes are poikilothermic organisms on which external environment directly influence their body temperature (Hawley, 1988) but the effect of meteorological variables on vector populations could be different amongst geographical locations with diverse climate conditions (Tuladhar et al., 2019). In the current study, decline in Aedes population during extreme temperatures of cold weather (January to March and December) and hot weather (May to July) was observed in Multan. The peak population of the Aedes larvae during 2014-2016 was collected from Multan when temperature was calculated between 20-32 oC during September to November, and was in agreement with the results reported previously by Delatte et al. (2009) who found optimum immature stages development at 29 oC and Mohammed and Chadee (2011) whom proposed significant mosquito’s eggs hatching success at 24-35 oC.

As it is reported previously that in the South-Eastern Asia, female vector preferred to lay its eggs in domestic containers and precipitations plays vital role in its distribution and abundance (Aziz et al., 2012) indicated that water is one of the important factors involved in the growth and breeding of larvae. In this study, the highest rainfall recorded in July, 2015 (138.9 mm) then in August, 2016 (69 mm), increased the emergence of Aedes larvae population from August to November during 2015 and 2016 suggested that the rainfall has positive correlation with the breeding of larvae. These results are in accordance with the earlier findings that higher rainfall plays vital role to enhance the Aedes population (Vanzie, 2008; Aziz et al., 2012). Additionally, the maximum population of Aedes larvae at 50-65% relative humidity in September to November during 2015 and 2016 demonstrated that relative humidity in the atmosphere due to higher rainfall had positive association with the emergence of larvae. The same findings were reported by Costa et al. (2010) that the gradual reductions in egg fertility at 60% relative humidity with increase in temperature, although such effect was not found at 80% relative humidity at 25 ºC and 30 ºC witch also confirmed and authenticated this study findings.

CONCLUSION

The environmental variables played major role in seasonal emergence of Aedes mosquito. Favorable environmental variables (watery environment or rain fall, temperature between 20-33 oC and suitable relative humidity between 50-65%) enhanced the growth of the Aedes population in Multan during this study especially in November 2015. Designed study and its findings will help in forecasting dengue epidemic especially in dengue endemic regions and will be helpful to control the spread of Aedes populations and dengue fever infestations under the impact of environmental variables by earlier adopting integrated vector management strategies.

Declarations

Acknowledgements

We are thankful to Primary and Secondary Healthcare Department, Punjab for providing us supportive environment and help us in Aedes mosquito collection through its field officials and officers.

Statement of conflict of interest

All authors declared that there is no conflict of interest.

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