7.4 FLY AND MOSQUITO MANAGEMENT Essay Example

Fly and Mosquito Management in Nepal

Executive Summary

Nepal is a country in the Middle East with mountains and plains alike. The country experiences both hot and cold climate. The tropical temperatures in the low-lying plains provide an ideal habitat for breeding of mosquitoes. Nepal does not face many problems from mosquitoes as it is with most tropical countries. However, the onset of the summer brings with it an increased mosquitoes population which then becomes a great problem. Malaria and elephantiasis are the most common mosquito-borne diseases in Nepal. The border between India and Nepal is so porous that migrants infected with these diseases can easily cross into India. Throughout the twenty six years of CIWEC clinic, there were only two reported cases of vivax malaria that have emanated from within Nepal borders. The risk of malaria is much reduced in comparison with dengue and elephantiasis in Kathmandu or the mountainous areas.

Large populations of mosquitoes have been majorly recorded in the plains, areas like Kailali and Kanchapur in the western parts of Nepal, Mahottari in the eastern central parts, Nawalparasi in central terai, Morang in the far eastern parts, and Kavre valley which experience hot and humid climate, although this is not confined to areas like these. It is common knowledge that mosquitoes need stagnant water for breeding, mosquitoes can today be found in Kathmandu, especially in the summer.

Table of Contents

Executive Summary 1

Introduction 2

Context of the Problem 2

Trade-off Analysis 4

Mosquito Control Measures 4

The Sand Fly 5

Control of the Fly 5

Objective 6

Methodology 6

Findings 6

Conclusion 10

References 12

Introduction

According to the Nepal’s Ministry of Health Department of Health Services, Kavre is rated as the district heavily affected with malaria. The months of July and September appear to be the time when transmission is very high. The statistics obtained from the epidemiology and disease control division, sixty five in every seventy five districts appear to be highly prone to malaria – infecting about seventy nine per cent of the twenty eight million population of the country. Thirteen districts are ranked as most risky, which include Kavre, which have temperature ranging between twenty to thirty degrees centigrade. The altitude of these areas of below two thousand exposes the as good areas for mosquitoes to breed. This is not the only region as there are other more regions including areas in the east, mid-west, far west and central parts of the country. 

Nepal is also highly infested with sand flies which are the carriers of Visceral leishmaniasis parasite (VL). This parasite is considered to be as large as mosquitoes in the spread of parasitic disease. This parasite does not receive as much attention and this makes it the second largest parasitic killer spread by disease vectors. The disease is most common among the poor population of. VL is has no vaccine. Control measures should be taken including detecting the disease early enough, treating those infected and reducing the vector population to keep the disease transmission in check.


Context of the Problem
Nepal has different geographical distinction which can be divided into hills (“pahad”), plains (“terai”) and mountainous regions (“parbat”). In terms of administrative units, Nepal is divided into the central, eastern, far western and mid-western regions. The areas most affected are in the eastern region of Terai, due to the hot and humid climate in the area. According to the Nepalese government statistics, the Terai is the more densely populated area compared to the mountain and hill areas. The mortality rates not as high, the number of annual reported deaths standing at between five and seven. The rate of occurrence is however quite high (between 5,000 and 7,000 annually). The division of epidemiology confides that eradicating malaria would not be easy considering the warm and humid temperatures of Nepal. 

Furthermore, Nepalese are resistant to change in behavior especially among the communities considered more prone to infections. There are no nets in these areas and the people do not spray their houses for mosquitoes. Moreover, those already infected are reluctant to seek medical attention, making these people highly vulnerable, (Thakur G, 2012).

People need not be impressed by the low death rates since the malaria epidemic has much more intensifying factors that should be worried about. Malaria prevalence in the months of july to September makes working very, (Thakur G, 2012). Nepal has experienced major ecological and environmental changes like deforestation and high intensity of migration. There has been therefore rampant flooding and landslides, and also waterlogging, which can be attributed to the rampant cutting down of trees. Migration also adds to the problem of malaria eradication. Workers are the largest group known for migrating to the cities of India and Nepal from villages which are highly infested with mosquitoes, thus ending up being infected with malaria.

Trade-off Analysis

Terai which borders India has experienced steady industrialization, leading to water logging, where malaria vector intensity grows. The actively migrating Nepal’s population makes malaria control difficult as they keep on moving into malaria infested regions in India such as Assam and also north eastern states that migrate to look for livelihood. These migrants then go back to their residences already infected thus transmitting the disease, (Thakur G, 2012). The UN World Health Organization (WHO) rates malaria as the most serious health challenge in Assam including other states in the east. 

Mosquito Control Measures

The government is targeting at the poor communities with the aim of distributing two million and two hundred thousand mosquito nets and also offering better health services in public health facilities. This would be achieved offering free diagnostic services and in case of any incident, the patient is treated immediately, (Thakur G. 2012).

Many achievements have been made by Nepal n combating malaria related death since the inception of the programme aimed at combating malaria in 1954. As per the statistics obtained from the epidemiology division, the annual reported malaria cases as by 1954 was two hundred thousand per year. This has since reduced to around five thousand cases at present. In line with Millennium Development Goals, the country is aiming at halving the number of malaria cases by 2015. 

The Sand Fly 

Apart from the malaria, a new vector-borne disease is gaining foot in Nepal and the larger Indian subcontinent. With one hundred and fifty million people at risk of getting infected, over forty thousand incidences have been reported every year. This disease is called Visceral leishmaniasis (VL), also known as kala-azar, (WHO 2005). The causative agent for VL in the areas of Bangladesh, Nepal and India is Leishmania donovani (Laveran & Mesnil). This parasite is common in and transmitted Phlebotomus argentipes (Dinesh et al. 2000).

Control of the Fly

The disease control involve detecting it early, treating the infected people and controlling the population of the insect. The major method in current use in controlling P.agentipes is the indoor residual spraying (IRS). The method was ideal due to its effective use in the control of VL as well as its eradication of mosquitos around 1970. The method has however failed to prove its effectiveness in India, despite these efforts. Insecticide treated nets (ITN) have been recommended to be used in place of IRS or as a compliment to IRS (Ostyn et al. 2008). A study codenamed the KALANET community trial confirmed the effectiveness of (ITN) n reducing P. argentipes population by twenty five per cent.

Blood feeding rates which include the percentage of females fed in blood and human blood index (HBI) are measures that can be used to gauge the effectiveness of personal protection. This is done to keep track of vector control interventions. These nets can be instrumental in reducing the blood feeding rates of the sand flies and at the same time improve the effectiveness of the bed net barrier. Untreated nets can also provide some form of protection against the P. argentipes, as observed in studies conducted in Nepal.

The estimation of personal protection in areas prone to VL infections is not easy. This can be so considering the use of human-landing catches and study experiments conducted n huts, which difficult to prove in terms of ethics, place and time of potential fatality of the disease. This disease is different from malaria in that the field workers are more at risk of death from the disease due to the lack of prophylactive that is effective against the disease.

Objective

This study was aimed at investigating the difference untreated nets make on the blood feeding rates and anthropophagic behavior of P. argentipes.

Methodology

The KALANET trial acted as a basis for this study as some twelve structures from the study, picking six areas in the countries of India and Nepal. Twenty five households were randomly selected and ten minute aspirations conducted in them in September 2006. Some ten households that were found to have the highest number of P. argentipes in every cluster were put under study with the ten cattle sheds that were nearest to them. These were studied for fifteen to sixteen months from September 2006 in India and Nepal. Treated nets were then distributed in six of the clusters, three in each country in December 2006. No nets were distributed to the other 6 clusters so that they can be used as controls. Light traps (LT) were used to capture the insects each month during the night.

Findings

Untreated nets were provided to the ten selected households during the sand fly collection nights in intervention and control structures. This activity was carried out in December 2006 in Nepal and January 2007 in India. This was in the first month that LNs were provided to the trial structures. In intervention households LNs were returned on the following morning. The untreated nets were used so as to appreciate the reduction on P. argentipes indoor density in the intervention clusters to the comprehensive distribution of LNs. This was in contrast to a local household effect induced by the presence of the LN during the night of capture (Picado et al. 2009).

The consent of the head of the household was obtained where sand flies were to be collected. Examination of the P. argentipes collected by LT and aspiration was done by the use of a binocular dissecting microscope so as to identify the gender and the status of the blood consumed. The P. argentipes, already fed in blood, were squashed individually onto Whatman’s #1 filter paper to determine the source of the blood meal.

Determination of the source of the blood meal in the blood-fed P. argentipes was done by the use of an ELISA. These were insects obtained from the six KALANET Nepal clusters. Testing was done to establish whether the blood originated from dog, human, rat, bovine, chicken or goat.

As untreated nets were only provided to households during sand fly collection nights after the first three or four months in Nepal and India, respectively, it was hypothesized that any observed change between pre and post-intervention blood feeding rates and human index in female P. argentipes would be best explained entirely by the personal protection provided by the untreated nets. This was because untreated nets were only provided to households during the night of sand fly collection after the first three months in Nepal and four months in India.

The effect of untreated nets on blood feeding rates was tested only on control clusters in India and Nepal because reduction in blood feeding rates in the LN clusters could be due to the personal protection provided by the untreated nets on the night of sand fly capture as well as the presence of LNs throughout the cluster. The effect of untreated nets on human index was however assessed using the results from households and cattle sheds from both the intervention and control clusters in Nepal.

The untreated nets were assessed on the basis of «before and after intervention» using two data sets: (i) collections before and after LT intervention were compared in control households in India and Nepal to determine the effect of the nets which were not treated on the blood feeding rates and (ii) collections done before and after intervention were compared from intervention and control households and cattle sheds in Nepal to evaluate the impact of the nets which were not treated on human blood index. A negative binomial mixed model, which can be adjusted by country, using household or cattle shed as a random effect to control for repeated measures was used. A dichotomous variable representing the time (i.e. pre and post-intervention) was the explanatory variable. In the blood feeding rate and HBI models the number of blood-fed P. argentipes and P. argentipes with human blood per household were the response variables. The term interaction between intervention and time variables was tested to determine whether the effect of the use of untreated nets varied between the two groups.

The Indian Council of Medical Research, the Ethical Committee of the BP Koirala Institute of Health Sciences (Dharan, Nepal), Institute of Tropical Medicine (Antwerp, Belgium) and London School of Hygiene and Tropical Medicine (UK), all gave the clearance for this study to be conducted.

The study collected a total of one thousand and sixty four female P. argentipes using LTs from fifty eight households in the 6 KALANET control clusters. From this population, a hundred and forty three flies, representing eleven per cent were fed in blood. There was significant reduction in blood-fed rates in all the control structures (from around twenty one to two percent), as shown in Table I. there was significant drop in female P. argentipes which fed on blood, which is indicated by the negative binomial model. There was 85.5 per cent drop in blood-fed P. argentipes. Evaluated within 95% CI 76.5-91.1%, p < 0.001 on the introduction of untreated nets.

7.4 FLY AND MOSQUITO MANAGEMENT

The hundred and sixty eight blood-fed P. argentipes collected in Nepal were put under analysis to determine the source of the blood so as to determine the HBI. From the results obtained, 61.9 per cent fed on blood from humans, 4.2 per cent on dog, 0.6 per cent on chicken, 3 per cent on goat and 22.6 per cent on bovine. It was impossible to tell the source of 10.1 per cent of the blood samples. There were sample with a mixture of blood: one human/chicken, two human/bovine and one human/goat.

The evaluation of the effect of untreated nets was done by summarizing the ELISA results in Table II, and then dichotomized (i.e. human blood vs. non-human blood). The samples that could not be identified were assumed to be non-human blood to avoid wrong and misleading conclusions on the effects of untreated nets. HBI greatly reduced by 42.2 per cent (95% CI 11.1-62.5%, p = 0.014), as obtained by the negative binomial index, in the case where the nets were not treated. There was significant variation in the general reduction in control and intervention (interaction term: p = 0.014). as can be deduced from these results, LN distribution had a profound effect on the blood feeding behavior of P. argentipes. The great reduction in HBI in such areas compared to control areas backs this conclusion.This is as shown in Table II.

7.4 FLY AND MOSQUITO MANAGEMENT 1

Conclusion

From the above observations and results, it is clear that untreated nets can also be used to protect one from being bitten by sand flies as well as mosquitoes. The captured insects fed in blood reduced significantly by 85.5 per cent where untreated nets were used. There was a further reduction of HBI by 42.2 per cent. This means that the insects resorted to feeding on other blood sources when humans used untreated nets. This behavior was however majorly facilitated by the use of LNs. These findings are in agreement with other studies having been conducted elsewhere in Nepal and Bangladesh, (Bern et al. 2000, 2005). These other studies in Nepal, have however, not been able to discover the effect of ownership of treated nets to the incidence of VL in the areas of study, (Schenkel et al. 2006).

These studies did not have controls running concurrent with the experiment, thus the reduction in blood feeding index and HBI may have been brought about by other factors which can affect the study. An example can be changes in meteorological conditions like temperature and humidity which may affect host availability thus leading to uncertain contact between host and the vector. More elaborate entomologic studies should be conducted to back the validity of the results obtained from this study.

References

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  3. Oliveira Filho AM, Melo MT 1994. Vectors control importance on leishmaniasis transmission. Mem Inst Oswaldo Cruz 89: 451-456

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