Dengue Virus In Mauritius Biology Essay

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The Republic of Mauritius is a small island nation of four inhabited and several other islands located in the Southwestern Indian Ocean. The island of Rodrigues and other smaller islets also form part of the country. The area of the country is of about 2,040 sq km. The Republic of Mauritius is a tropical country located at latitude 20° 18' 0 S and longitude 57° 34' 60 E. In the south west of the Indian Ocean, Mauritius is located to about 2000 kilometers from east west of Africa and some 800 kilometers from Madagascar island. The positioning of Mauritius makes the latter a tropical country with moderately lofty temperature throughout the year. Winter and summer are the seasons that manifest onto the island.


Fig: World map showing location of Mauritius Island in the Indian Ocean

The island of Mauritius finds itself as one of the most accessible islands in the Indian Ocean. Situated amid Réunion island and Rodrigues island, the island of Mauritius has gained the reputation, through the course of time of that of the 'key and star' of the Indian Ocean. The Mauritian population estimates for the year 2008 was about 1, 260, 781 with an annual growth rate of 0.7 %.

Since the country is undergoing major developmental changes many industries have implanted here and thus the number of expatriates in the country is on the rise. These people may be a carrier of the disease and of course those Mauritians visiting the dengue endemic areas can also become infected and bring the disease in the country.

It is an indisputable fact that during the lapsed decades, Mauritius has witnessed a multitude of diseases. The most prominent and recent one being Chikungunya which has infested merely about 12000 Mauritians. Furthermore, the history of diseases in Mauritius is marked with Malaria epidemics since colonial regimes and through the intensive effort of the Public Health sector, the latter has been proclaimed eradicated by the World Health Organization in 1973.

Some years ago many of the realm's citizens were not aware of what was dengue fever even though it had already occurred in the country but there was not mass infection by the virus. Providentially, the number of cases reported beforehand was only one or two and through the close collaboration between the Ministry Of Health and the infected person the situation was under control and hence no further positive case of dengue were recorded.

The Mauritian government is putting forward all steps to prevent an epidemic rather than to rush for controlling it when it has already hit the population. The Ministry of Health is working on a list which highlights all water retaining sites and is identifying the hotspots of such sites that are liable to cause proliferation of mosquitoes; this process is carried out each year. Furthermore, an action plan is being prepared by the ministry which gives a layout of which and what job is to be done by which section of the ministry or other stakeholders (anonymous, 2009).

Dengue viruses are transmitted by the Aedes species. Two known species the Aedes aegypti and Aedes albopictus are vectors of the disease. The Aedes albopictus can be found in large quantity all around the island whereas Aedes aegypti is said to be eradicated from the country. Surveillance on the abundance of mosquitoes is carried out by the entomological section throughout the year. All sites where mosquitoes that can be vectors of disease are seen, they are referred to the nearby health office for a larviciding to be carried out at that place and in the vicinity.

Aedes albopictus (Skuse) is known as the Asian Tiger mosquito (Robertson and Hu, 1988). Aedes albopictus is native to Southeast Asia, but now occurs throughout the world. The worldwide spread of Aedes albopictus during the precedent 20 years has caused apprehension in the midst of public health officers and scientists over the possibility that the introduction of this species will amplify the risk of epidemic dengue fever and other arboviruses in countries where it has become established (Gubler, 2003).


The aim of this study is mainly to evaluate the effectiveness of the control measures taken to prevent dengue fever in Mauritius. Emphasis will be laid on the steps taken before, during and after the disease occurrence. This might highlight the shortcomings that Mauritius face in order to manage outbreaks of diseases.

Objectives of study

The objectives of this dissertation are to evaluate the management, procedures and legislation that are implemented in Mauritius during outbreaks of dengue fever. Furthermore, most interest is geared towards the application of chemicals, preventive measures, and health education of the public carried out by the Ministry of Health & Quality of Life to prevent the occurrence of the disease and also to annihilate if ever found in the island. To elucidate the effectiveness of fogging, larviciding and health education of the public.



2.0 Dengue

2.0.1 General considerations

Dengue is a flu-like mosquito-borne disease and has a soaring capacity for epidemic outbreaks, which according to the World Health Organization (2009) affects 50-100 million people each year in the tropical and sub-tropical areas of the world. Dengue is cited as being one of the most significant mosquito-borne disease affecting humans and as a major international public health concern (WHO 2009). Dengue fever is predominantly transmitted by Aedes species which have adapted themselves to living near human habitation (Hales et al., 2002).

During the last decade, dengue infection along with its complications has been on the rise all over the world. Their geographical spread is increasing: only 5 countries documented dengue in the 1950's but to date there are more than 100 countries reporting the incidence of dengue fever and dengue hemorrhagic fever (Guha -Sapi & Schimmer, 2005). Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas (WHO, 2009).

Dengue fever and dengue hemorrhagic fever were first identified in the 1950's, during the dengue epidemics in Philippines and Thailand and by 1975 it had become a leading cause of hospitalization and death among children in many countries found in that region (Lloyd, 2003). Dengue-like epidemics occurred in Egypt and on Java in 1779, but these may actually have been caused by the chikungunya virus (Carey, 1971)

The dengue virus is a member of the family Flaviviridae virus, transmitted through the biting of infected Aedes aegypti and Aedes albopictus mosquito. The Aedes aegypti mosquito normally bites indoor and late in the afternoon whereas the proficient mosquito Aedes albopictus ia an aggressive daytime biter, which is also known to bite early in the morning, late afternoon (Knight and Hull, 1952) and at night (Murray and Marks, 1984). This biter is usually an outdoor biting mosquito, but it also bites indoors (Hawley, 1988). Generally the mosquitoes bite at ground level (MacDonald and Traub, 1960, cited in Hawley, 1988). Females will bite any area of exposed skin, but prefer the ankles and knees (McClelland et al., 1973; Robertson and Hu, 1935).

Dengue or dengue-like epidemics were reported through- out the 19th and early 20th centuries in the Americas, Southern Europe, North Africa, the Middle East, Asia and Australia and on various islands in the Indian Ocean, South and Central Pacific and the Caribbean (Ehrenkranz et al, 1971).Generally these epidemics consisted of nonfatal feverish illnesses, often coupled with rash and either muscle or joint pains (Carey, 1971).Deaths occurred during dengue epidemics in Australia in 1897 and in Greece in 1928, when over 1000 deaths were reported (Halstead, 1980). Hemorrhagic demonstrations, including gastrointestinal hemorrhage, were described during dengue epidemics in Texas and Louisiana in 1922 (Scott, 1923). Nevertheless through the first half of the 20th century, dengue was generally described as a self-limited, nonfatal febrile illness, with occasional hemorrhagic manifestations such as petechiae, epistaxis, gingival bleeding and menorrhagia that only rarely resulted in more severe or fatal outcomes.

Dengue virus belongs to the genus Flavivirus, Family Flavivaridae and there are four serotypes of the virus (DEN-1, DEN-2, DEN-3 and DEN - 4). All the four serotypes can cause dengue fever, dengue hemorrhagic fever and even dengue shock syndrome (Ramchurn et al, 2009). The four viruses are closely related but are distinct. Millions of people residing in tropical areas of the world are affected by epidemics of dengue fever. Dengue fever is associated with the severe form dengue hemorrhagic fever/ dengue shock syndrome (DHF/DSS) that is seen mostly in children and nevertheless adults also are attained the disease.

Dengue fever is a very infectious mosquito borne viral disease characterized by either a mild febrile syndrome or the classic incapacitating disease with abrupt onset of high fever, severe headache, pain behind the eyes, muscle and bone or joint pains, nausea and vomiting and rash. Skin hemorrhages are not uncommon. Leukopenia is usually seen and thrombocytopenia may be observed (WHO 1997).

2.0.2 Pathogenicity of Dengue fever:

1. Asymptomatic and mild infection

It is very common.

2. Dengue Fever (primary infection)

There is no plasma leakage. Patient presents with Influenza like illness-fever-arthralgia- rash syndrome. DF is characterized by high fever; sever frontal headache; retro-ocular pain; muscle (break bone fever) and joint pain; and generalized maculopapular rash. Conjunctiva may be injected (become red). Nausea, vomiting diarrhea, abdominal pain are other common problems. Photophobia, sore throat, lymphadenopathy and bleeding tendencies are not uncommon. Unlike DHF, tourniquet test is positive in only one-third of the patients. The illness lasts 5 to 7 days.

Immunity is lifelong. On the contrary immunity or prior exposure increases the risk of Dengue Hemorrhagic Fever or Dengue Shock syndrome. Some patients would experience depression (heart break fever) and fatigue for several months after recovery.

3. Dengue Hemorrhagic fever

The prominent feature is bleeding. It is caused by either re-infection by a different dengue virus serotypes or rarely by primary infection (virulent serotypes or strains). It is common in children in Under 15 years of Age in Asia whereas in South America it is observed in all ages. It is characterized by sudden rise in temperature and other manifestations of Dengue fever. Tourniquet test is positive in half of the patients. Petechiae, easy bruising, gingival bleeding and epistaxis are common. Gastrointestinal bleeding observed in patients with severe illness. Hepatomegaly and splenomegaly are common in children.

4. Dengue Shock Syndrome

The prominent feature is hypotension (hypovolumic shock). It is uncommon after 15 years of age. The clinical features include weak pulse with narrow blood pressure (<20 mm of Hg), cold and clammy skin. Pleural effusion, ascites and intense abdominal pain may predict eminent Dengue shock syndrome (Rigall-Pewrez et al.1998).

2.0.3 Mode of transmission of dengue virus:

Chikungunya and dengue viruses are transmitted to humans by the bites of infected mosquitoes. In contrast, Aedes albopictus is abundant and may be the only important vector of these viruses on the islands. Both species bite mainly during the daytime, particularly in the early hours after dawn and for 2-3 hours before darkness. Aedes albopictus is more active outdoors whereas Ae. aegypti typically feeds and rests more indoors (WHO 2008).

In the cycle of dengue, the vertebrate host is man and the Aedes species the vectors. The disease is acquired only when bitten by female mosquitoes, as the female feed on blood in order for the development of their eggs whereas the male mosquitoes are not infectious due to the fact that they feed only on nectars (from fruits, flowers) rather than blood. In 8-10 days the infected mosquito is able to transmit the virus to other people. Thus the cycle of transmission takes only 14 days. One dengue-infected female mosquito is capable of biting and infecting several people during one feeding session.

The Aedes species have adapted themselves to the human habitation and thus can be frequently found around places where there is human habitation. The dengue mosquito is sometimes dubbed the 'cockroach of mosquitoes' because it is truly domesticated and prefers to live in and around people's homes. It does NOT breed in swamps or drains, and does not often bite at night.

The dengue mosquito frequents backyards in search of containers holding water inside and outside the home, such as: cans, buckets, jars, vases, pot plant dishes, birdbaths, boats, tyres - discarded with no rims, roof gutters blocked by leaves striking containers, tarpaulins and black plastic.

Figure 2.1: showing blocked state of rain water drain and a good site for breeding of mosquitoes.

It can also breed in natural containers like:


fallen palm fronds.

In drier conditions it also breeds in water in subterranean sites such as: wells, telecommunication pits, sump pits, gully traps.

Transmission cycle of dengue results from a complex system based on several main constituents like: the density of susceptible hosts, environmental conditions and the presence of one or more serotypes of the dengue virus. The number of confirmed dengue cases has been increasing owing to the fact that the world is undergoing rapid urbanization and its population is also on the rise, disposal of non-biodegradable containers, rapid transportation and poor living conditions such as poor water supply and very rare scavenging services at squatter areas (Satwant, 2001).

Dengue virus is one of those pathogens that depend almost entirely on human for its survival. A low concreteness of the vector, the Aedes mosquitoes does not readily imply that infection rate will be low. Since the mosquitoes have the propensity to take blood meals more often, it increases the chance of a person being bitten by an infected female Aedes mosquito hence enhancing the contraction and transmission of the virus.

Various studies have shown that the Aedes albopictus is able to transmit all the 4 serotypes of dengue. Aedes albopictus mosquito can serve as an important maintenance vector of dengue viruses in endemic areas, and new endemic areas may be initiated by importation of vertically infected eggs (Gubler, 2002). That is the infected Aedes mosquito can pass the dengue virus to its progeny and when the eggs will develop into mature mosquitoes they will be already infected, hence capable of causing infection of human beings or even pass the virus to their progeny.

Figure 2.2: how dengue virus is transmitted by Aedes aegypti (source: CDC Dengue Slideset).

The transmission cycle of dengue virus by the mosquito Aedes aegypti begins with a dengue-infected person. This person will have virus circulating in the blood-a viremia that lasts for about five days. During the viremic period, an uninfected female Aedes aegypti mosquito bites the person and ingests blood that contains dengue virus.

Although there is some evidence of transovarial transmission of dengue virus in Aedes aegypti, usually mosquitoes are only infected by biting a viremic person. Then, within the mosquito, the virus replicates during an extrinsic incubation period of eight to twelve days. The mosquito then bites a susceptible person and transmits the virus to him or her, as well as to every other susceptible person the mosquito bites for the rest of its lifetime. The virus then replicates in the second person and produces symptoms. The symptoms begin to appear an average of four to seven days after the mosquito bite-this is the intrinsic incubation period, within humans.

While the intrinsic incubation period averages from four to seven days, it can range from three to 14 days. The viremia begins slightly before the onset of symptoms. Symptoms caused by dengue infection may last three to 10 days, with an average of five days, after the onset of symptoms-so the illness persists several days after the viremia has ended (CDC Dengue Slideset).

2.0.4 Lifecycle of Aedes mosquito:

The mosquito goes through four separate and distinct stages of its life cycle and they are as follows: Egg, Larva, pupa, and adult. Each of these stages can be easily recognized by their special appearance.

Source: [accessed on 21/12/09]

Figure 2.3: Life cycle of Aedes mosquito

Egg: Eggs are laid one at a time and they float on the surface of the water. Aedes species do not make egg rafts but lay their eggs separately. Aedes lay their eggs on damp soil that will be flooded by water. Most eggs hatch into larvae within 48 hours.

Larva: The larva lives in the water and come to the surface to breathe.The larva feed on micro-organisms and organic matter in the water. On the fourth molt the larva changes into a pupa.

Pupa: The pupal stage is a resting, non-feeding stage. This is the time the mosquito turns into an adult. It takes about two days before the adult is fully developed. When development is complete, the pupal skin splits and the mosquito emerges as an adult.

Adult: The newly emerged adult rests on the surface of the water for a short time to allow itself to dry and all its parts to harden. Also, the wings have to spread out and dry properly before it can fly.

The egg, larvae and pupae stages depend on temperature and species characteristics as to how long it takes for development. Also, some species have naturally adapted to go through their entire life cycle in as little as four days or as long as one month.

Under optimal conditions, the egg of a mosquito of the genus Aedes can hatch into larvae in less than a day. The larva then takes about four days to develop in a cocoon from which adult mosquitoes will emerge after two days. Three days after the mosquito has bitten someone and taken in the blood, she will lay eggs and the cycle begins again.

In the Aedes mosquito family only the female bites because it requires protein to develop eggs, therefore if it bites a person infected with the dengue virus the mosquito becomes infectious after approximately 7 days. The mosquitoes are known to be biting at a highest frequency at dawn and dusk. Some more facts:

The average lifespan of a mosquito of the genus Aedes in Nature is 2 weeks

Mosquitoes may lay eggs about 3 times in his life, and about 100 eggs are produced each time.

The eggs can live in dry conditions until approximately 9 months, after which they can hatch if it is subject to conditions, i.e food and water

Source: [accessed on 05.12.09]

Figure 2.4: Picture of lifecycle of Aedes mosquito in water

2.0.5 Investigation for dengue infections:

Laboratory results

CBC- Leukopenia, neutropenia, lymphocytosis

-Thromocytopenia - moderate in Dengue fever and < 100,000/ml in DHF/DSS


Chest x-ray shows pleural effusion and occasionally pericardial effusion


To detect pericardial effusion and ascites


Specimen- Serum should be send to virology laboratory to detect the virus or for serology.

Virus isolation has a sensitivity of 50 %. Culture is done in cell line derived from A. albopictus cell. Immunoflurescent techniques are used to detect viral replications. The virus can be isolated in patients with fever.


IgM is detectable in 90 % of patients by the 6th days of illness. Serum collected early may give false negative result. The IgM may remain detectable for 2-3 months. It is not possible to identify serotype with serological tests. IgM Positive result may suggest recent infection with Dengue fever. However definitive diagnosis can only be made if the virus is isolated or the virus genome is detected by PCR. Once the IgG is detected, it will remain positive for years. Seroconversion or increase in titer may indicate recent infection.

The appropriate samples for PCR test include plasma and serum. Molecular test is highly sensitive but it can be used in patients only with viraemia (Rigall-Pewrez et al.1998).

2.0.6 Treatment:

The managing of dengue fever is supportive with bed rest, passable fluid intake, plus control of fever and pain with antipyretics in addition to analgesics (e.g. paracetamol). For the supplementary ruthless manifestations of dengue virus infection, correct management requires early identification and swift intravenous fluid substitution. In severe cases blood transfusions may be required.

There is currently no vaccine is available to shield against dengue infection. There are three major concerns in the development of a dengue vaccine. Firstly is the possibility that it could lead to antibody-dependent enhancement of infection and thus produce DHF/DSS. Candidate vaccines based on live attenuated viruses should therefore contain all four serotypes to give comprehensive protection without adverse side effects. Another concern is the possibility of virus evolution through genome recombination (Liew, 2006).

A third concern is that the vaccine may produce adverse reactions, for example, recently a tetravalent live attenuated vaccine was tested in human volunteers and in children, phase I and phase II trails have shown mildly adverse reactions with monovalent vaccines, but more frequent and significantly more severe reactions with the tetravalent vaccine. The present lack of a successful vaccine against the dengue virus, causes prevention methods to be approached by reducing disease vector population, with Integrated Pest Management (IPM) programs for mosquito control.

These utilize a combination of control strategies, including mosquito surveillance, source reduction, eradicating larvae and eradicating adult mosquitoes. Eradicating adult mosquitoes alone is ineffective in controlling mosquito populations because it is difficult to treat the inaccessible habitat of the adults. Mosquito larvae are left to continue their development, and they quickly replace the adults. However, mosquitoes can build up resistance if pesticides are overused.

2.0.7 Dengue fever in Mauritius:

Dengue virus infections are emerging as the major ones in Southeast Asia. Global warming may worsen the occurrence of dengue fever. Since very last few years mixed outbreak of chikungunya and periodic cases of dengue fever have been reported on Réunion Island and other South West Indian Ocean countries. From March 2005 till March 2006 it is estimated that about 204000 people in Réunion island may have been infected by the chikungunya virus, which furthermore shows that there is presence of the transmitting vectors of the disease on the island which are also the vectors of dengue fever as well. Hereafter, the other South West Indian ocean countries were not spared from infection from the chikungunya virus.

An outbreak of dengue fever was reported in Madagascar more specifically in the city of Toamasina that started mid-January 2006 and rare cases of chikungunya were also reported mid-February. Maldives also have suffered from a dengue outbreak in year 2006 where 602 people were suspected to be infected among which there were some severe form of dengue fever that is 64 dengue hemorrhagic fever cases and 9 cases of dengue shock syndrome (WHO 2006).

In Mauritius the first case of dengue fever dates to the 1976's and it was contained thus limiting the disease from spreading. Then we had a case of imported dengue from a person who visited an endemic dengue area in January 2008 (CDCU). The main vectors of the disease remain the Aedes mosquitoes, among which the Aedes aegypti mosquito is the primary vector and Aedes albopictus the secondary one. The mosquito found to be spreading dengue fever and Chikungunya in Mauritius is the Aedes albopictus (CDCU 2009). It is to be noted that in Mauritius we had both the Aedes aegypti and Aedes albopictus mosquitoes, due to the intense anti-malaria campaign during the year 1952 the primary carrier of the dengue fever, the Aedes aegypti have been successfully eradicated. Still very minute amounts of this mosquito can be seen whereas the Aedes albopictus is abundant. Dengue is transmitted from person to person through the biting of infected mosquitoes.

Most recently we had a short-lived epidemic of re-emerged dengue fever in Mauritius that started in the month of June 2009 which was imported. The mild fever was first localized in the city of Port Louis, where there were 192 cases and then we did have some sporadic cases in other regions of the island. Mosquito fogging and larviciding started on 3 June 2009, covered the whole of Port Louis and were repeated every seven days. Mosquito fogging was carried out outdoors early in the morning, early evenings and sometimes till late in the evenings (Dengue Unit 2009).

The Ministry of Health and Quality of Life of Mauritius took the situation as being severe and all medium possible to contain the disease were put into action. Like the Special Mobile Force and manpower from other Ministries which joined the Ministry of Health to fight the dengue fever. Public awareness campaigns on the necessity to search and eliminate mosquito breeding sites at home and in the neighbourhood and to protect oneself against mosquito bites were carried out through radio, television and the press through a public private partnership. Detailed information leaflets were also distributed, door to door distribution of pamphlets showing pictures of possible breeding sites for mosquitoes and products to be used to prevent mosquito bite were carried out by the primary health care personnel. Target groups included the public, community groups and school children (Ramchurn et al, 2009).

By the end of the month August no new or suspected cases of dengue were recorded in any of the country's hospital. But still the control and prevention program were continued throughout the island as the summer season was coming near hence reappearance of the dengue fever was possible due to the ambient temperature, favorable for larvae development. The fear of having the virus again was due to the possibility of the infected mosquitoes to pass the virus to their progeny. Fortunately, till February 2010 no suspected or confirmed case of dengue fever was reported from any health institution of the country.

2.1 Vector surveillance and control program

Ever since mosquitoes are capable of transmitting diseases like dengue and chikungunya, till now it has not been possible to eradicate the mosquitoes completely from their originating site. The best way to monitor or control vector-borne diseases is to control or limit the population of the vector to such an extent that disease transmission is very low or even stopped. In order to achieve this goal, it is imperative to know all about the mosquito involved in the transmission of the disease.

Detailed knowledge of all aspects such as the breeding sites, different features of the mosquito at different stages, feeding habits, mating, resting and structure and most importantly without forgetting the lifecycle of the mosquito, are the main required things in order to be able to break the chain of transmission. Furthermore, the only way to prevent infection of people who have not suffered from dengue is to control the population of dengue vector (Ooi et al.2001) and of course personal precaution has also proved to be effective in reducing the risk of being infected by a mosquito.

Since no vaccine is yet available for dengue the only mode to control dengue fever is the control the amount of the disease vector that is of the Aedes mosquitoes. The control strategies of these mosquitoes are 1) carrying out larviciding -spraying a chemical called abate in any water retaining place which kill the larvae of the mosquitoes hence interrupting the cycle to be completed, 2) fogging operation- a thermal fogger is used to propel fumes of Aqua K-Othrine® which when is in contact with a mosquito kills it, thus the amount of developed or simply mature mosquitoes are reduced and 3) health education- talks are organized for the members of the public, for children in schools, colleges, etc…

Entomological survey is an important and integral part of dengue prevention and control. The effect of the intervention by the community can directly affect the ecology of the vectors that is the Aedes mosquitoes.

The Communicable Disease Control Unit (CDCU) is the unit which is mostly concerned for the control of communicable diseases such as Malaria, Dengue fever, Chikungunya, and other infectious diseases. In Mauritius, surveillance, disease prevention and education of infectious diseases are mainly carried out by the Health Inspectorate Cadre. In Mauritius, we have the Public Health Act (Section 32A)which is used in case where there is presence of a mosquito borne disease in the island.

The potential for predation to prevent pathogen invasion or reduce disease prevalence in a host population also has implications for the biological control of vector populations. Predators have been introduced, or proposed, as biological control agents of vectors for various diseases such as malaria, dengue fever and Lyme disease (Jenkins 1964; Legner 1995; Stauffer et al. 1997; Samish & Rehacek 1999; Scholte et al. 2005; Kumar & Hwang 2006; Ostfeld et al. 2006; Walker & Lynch 2007). Several recent studies suggest that predator introductions led to a decline in local cases of dengue fever in Vietnam and Thailand (Kay & Nam 2005; Kittayapong et al. 2008), and malaria in India (Ghosh et al. 2005; Ghosh & Dash 2007).

2.2 Biology of Aedes albopictus (Skuse)

Mosquitoes are small, two winged insects belonging to the family Culicidae of the order Diptera. They are among the best known groups due to their importance as pests and as vectors of diseases. They are easily identified due to the combination of the following characters: long proboscis projecting head; presence of scales on the wing veins, a fringe of scales along the posterior margin of the wing, and the characteristic wing venation, the second, fourth and fifth longitudinal veins being branched (Miyagi and Toma 2000).

Female mosquitoes feed on blood and they have highly specialized mothparts for piercing host skin and blood sucking (Wahid et al. 2002). Aedes species are normally day-time bitters and active during the day. During this time, they have peaks of landing and biting activity. The peak time for Aedes albopictus occurred about one hour after sunrise and then before sunset (Abu Hassan et al. 1996). Nevertheless, the rate of biting varies depending on the mosquito age and time of the day (Xue and Barnard 1996).

Source: CDC, Public Health Image Library (PHIL)

Figure 2.5: Aedes Albopictus mosquito



3.1 Introduction

In this chapter, a summary of the various steps that was undertaken to finalize the research is attempted. The research work was started as from the month of September 2009 to the end of January 2010.


In order to assess the effectiveness of the control measures taken to prevent dengue fever, data were collected from the different partners who are involved in the control and prevention of dengue fever in Mauritius.

Such data were collected from books, newspapers, published articles, magazines and official statistics from the Central Statistics Office, Dengue Unit, Communicable Disease Control Unit and the Ministry of Health & Quality of Life.

Moreover, constructive discussion with people who are in touch with the matters connecting to the piece of work. Search through the internet, review of available documents and properly classifying the information that would be used during the study.


Questions related with the way of application of the different control measures were selected for analysis from the filled questionnaires. Moreover, each particular question was analyzed by using SPSS software which provided the frequency and percentages and hence Microsoft Excel 2007 was used to express the data in forms of percentages, tables, figures, graphs, pie charts and charts.

Chapter 4

Data Analysis

4.01 This chapter of the thesis will be dealing with the data collected from different stakeholders involved in the fight against dengue fever. Data collected mainly from the Communicable Disease Control Unit, Dengue Unit, and certain Health Offices of the country and the media will be expressed in figures. Much attention will be oriented towards the control measures in Port Louis, as the maximum number of cases occurred there and eventually the island in whole.

4.02 Progress of the disease through June 2009 in Port Louis

Figure 4.1: Number of cases each day during the month of June 2009

From figure 4.1 it can be seen that the first case was detected on 2nd June 2009 and the maximum number of cases reported to the hospitals was around the 10th to 13th day of the same month. The number of confirmed cases by the end of June 2009 had decreased to less than five.

4.03 Age of people infected with dengue virus


















Age of people who were diagnosed positive for dengue


Age: 1 means from 1- 10 yrs

2 means from 11-20 yrs

3 means from 21-30 yrs


Figure 4.2: Percentage of infected person according to their age

From the above chart (Fig 4.2) it can seen that about 34.55 % of the total number of cases (246 confirmed) of dengue were vulnerable ones that is the young and the elderly. The young may have been affected due to a not well developed immune system and the elderly who were aged from 50 years and above were probably infected due to the waiving of their immune system thus their body was not able to invade the dengue virus. The remaining 65.45 % were those who had fully developed immune system but still have been infected which may have been caused due to water accumulation nearby, visiting a person who was infected or even not covering thyself properly to prevent mosquito bite or not using mosquito repellants, in short terms it can be said that the individuals did not took proper precautions to avoid being infected.

4.04 Aqua K Othrine® used for fogging process

Figure 4.3: Amount of Aqua K Othrine® used daily for fogging operation in Port-Louis

Aqua K Othrine® is a chemical used in mixture with another chemical substance called Nebol®, in thermal foggers to kill adult mosquitoes. Normally, the fogger produces fumes which in fact are fine droplets of the mixture which when in contact with a mosquito causes its death. The first day of fogging was started on 2nd June 2009 with a minimum cubic centimeter of Aqua K Othrine® used, on the 7th day the maximum and throughout the rest of the days varying just a little in amount except for the 14th day.

4.05 Number of inspections carried out during the past 8 years throughout the


Figure 4.4: Statistic of the number of sanitary inspections carried out throughout the past 8


Starting from the year 2001 till 2005 from the graph (fig 4.4) the number of inspections carried out by the health inspectorate cadre shows a slight decrease and suddenly in 2006 the number increases to approximately 3 fold than that in 2005. In year 2007, the amount of inspections carried again decreases to 112,087 and eventually for 2008 the number decreases a bit more.

4.06 Number of sanitary notices served during the past 8 years

Figure 4.5: Number of sanitary notices served for none compliance with the

Public Health Act

Sanitary notices are normally issued to the author of nuisance, as for in this case the notices served were to cause removal of water collected in used tyres, drums, roof tops, etc… From the year 2001 till 2005 the number of such type of notices served was ranging between 4933 and 8013. For 2006 the figure was the highest with 10657 of notices served and for the remaining 2 years a gradual decrease was noted.

4.07 Number of contraventions taken for none compliance with the Public

Health Laws & Notices

Figure 4.6: Number of contraventions established under the Public Health Act

From the graph 4.6 can be elucidated that in year 2000 the number of contraventions established amounted to 92 and kept on increasing from year to year. Again in 2006 the number (312) was at its peak.

4.08 Percentage of people infected according to their gender

Figure 4.7: Percentage of each gender infected in year 2009

The total number of people who were confirmed to having the dengue fever arose to 246 amidst which 54% were female and 46% were male, irrespective of their age.

4.09 Number of staffs in health offices throughout the island

Number of officers

Health Inspectors


Health Surveillance Officers


Insecticide Sprayerman


Table 4.8: Number of officers for year 2008 in health offices in the island

Part II - Press cot Analysis

4.1 On 04/06/09 l'express journal wrote that there were 8 suspected dengue cases. In a press conference the Minister Rajesh Jeetah said that the country is equipped with a very good system of surveillance of diseases. In the mean time, blood samples were sent to South Africa for analysis. The minister also told the public to ensure that there is no water collection, to take necessary precaution to avoid being bitten by mosquitoes and use mosquito repellants, etc….

4.2 Again l'express journal reported that there are 2 more suspected cases. The minister said that with the close collaboration of the local authorities, they are running a national campaign of cleaning. With the help of other ministries campaigns for sensitization are being run.

4.3 News on Sunday paper on 09/4/2009 published an article saying Prevention and control relies heavily on reducing the number of natural and artificial water-filled container habitats that support breeding of the mosquitoes. This requires mobilization of affected communities. During outbreaks, insecticides may be sprayed to kill flying mosquitoes, applied to surfaces in and around containers where the mosquitoes land, and used to treat water in containers to kill the immature larvae. For protection during outbreaks of chikungunya, clothing which minimizes skin exposure to the day-biting vectors is advised. Repellents can be applied to exposed skin or to clothing.

4.4 News on Sunday paper published on 9th December 2009- There's no vaccination for dengue available yet, although trials are under way. So it's important when travelling to tropical regions to use mosquito repellents and to cover up with suitable clothing. Unlike the mosquito that carries malaria, which bites in the evening or at night, the mosquito that carries dengue bites during the day, so it's vital to protect yourself against mosquito bites during this time.