Environmental factors influencing malaria control

Introduction

Malaria is a mosquito-borne infectious disease of humans and other animals caused by parasitic protozoan (a group of single-celled microorganism) belonging to the genus Plasmodium. Malaria causes symptoms that typically include fever, fatigue, vomiting and headaches. In severe cases it can cause yellow skin, seizures, coma or death. The disease is transmitted by the biting of mosquitoes, and the symptoms usually begin ten to fifteen days after being bitten. If not appropriately treated, people may have recurrences of the disease months later. In those who have recently survived an infection, re-infection typically causes milder symptoms. This partial resistance disappears over months to years if the person has no continuing exposure to malaria (Caraballo, 2014).

The disease is widespread in the tropical and subtropical regions that exist in a broad band around the equator. This includes much of Sub-Saharan Africa, Asia, and Latin America. Malaria is commonly associated with poverty and has a major negative effect on economic development. The World Health Organization reports there were 198 million cases of malaria worldwide in 2013. This resulted in an estimated 584,000 to 855,000 deaths, the majority (90%) of which occurred in Africa (World Health Organisation, 2014).

Mode of transmission of malaria

The female anopheles mosquito is the vector for human malaria. Some 60 species of this mosquito have been identified as vectors for malaria, and their distribution varies from country to country. The infection is transmitted by the bite of an infected female mosquito – Anopheles (Fairhurst & Wellems, 2010). The mosquito usually bites during dawn and dust time. The mosquito becomes infected by biting a patient with malaria infection. When a mosquito bites an infected individual, it sucks the gametocytes, the sexual forms of the parasite, along with blood. These gametocytes continue the sexual phase of the cycle and the sporozoites fill the salivary glands of the infested mosquito.

Once the mosquito becomes infected, it remains so for life. The female mosquitoes can survive up to four (4) weeks under normal temperature i.e. 28°C to 30°C and humidity i.e. 60 to 80%. When this female mosquito bites the man for a blood meal, which it needs to nourish its eggs, it inoculates the sporozoites into human blood stream, thus spreading the infection (Mueller, Zimmermann & Reeder, 2007).

Other modes of transmission

Rarely malaria can spread by the inoculation of blood from an infected person to a healthy person. In this type of malaria, asexual forms are directly inoculated into the blood and pre–erythrocyte development of the parasite in the liver does not occur. Therefore, this type of malaria has a shorter incubation period and relapses do not occur.

1. Blood transfusion (transfusion malaria)

This is fairly common in endemic areas. Following an attack of malaria, the donor may remain infective for years (1–3 years in P. falciparum, 3–4 years in P. vivax, and 15–50 years in P. malariae.) Most infections occur in cases of transfusion of blood stored for less than 5 days and it is rare in transfusions of blood stored for more than 2 weeks. Frozen plasma is not known to transmit malaria. The clinical features of transfusion malaria occur earlier and any patient who has received a transfusion three months prior to the febrile illness should be suspected to have malaria (Owusu-Ofori, Parry & Bates, 2010).

  1. Mother to the growing foetus (congenital malaria)

Intrauterine transmission of infection from mother to child is well documented. Placenta becomes heavily infested with the parasites. Congenital malaria is more common in first pregnancy, among non – immune populations (Owusu-Ofori et al., 2010).

  1. Needle stick injury

Accidental transmission can occur among drug addicts who share syringes and needles (Owusu-Ofori et al., 2010).

Factors influencing malaria control

According to Fernando, Rodrigo and Rajapakse (2010) stated that there are several factors influencing malaria control which include:

  • Flooding: It provides great breeding ground for mosquitoes in riverside, urban communities. E.g. stagnant water from river.
  • Lack of adequate drainage system: When there is no proper drainage system to channel the water body.
  • Poor environment sanitation: When the over grown weed are not properly cut down, indiscriminate dump of refuse in the environment.

High trends of urban, per urban and rural transmission of malaria

Several African, South American The Middle East and South Eastern Asia cities where there is high prevalence of malaria  show a clear trend of increasing malaria transmission from urban to per urban to rural settings This is largely due to the fact that cities tend to grow outwards with perimeters consisting of relatively underdeveloped, poorly serviced settlements. Recent migrants from rural areas tend to bring their rural practices with them, creating a multitude of vector breeding sites, and poor quality housing provides less protection against mosquito bites.

Presence of natural vector breeding sites and environmental factor

The heavy burden of malaria in rural Africa is testimony to the ability of natural breeding sites to sustain vector populations. Natural breeding sites, although less common in urban areas, are nevertheless present. Temporary pools are less favoured because they may not provide sufficient time for eggs to develop and emerge as adults. It has also been suggested that they are more likely to be disturbed by human activity. A high groundwater table is particularly conducive to breeding sites as the absence of surface runoff allows pools of stagnant water to develop. The natural vectors breeding sites include: Fernado, Rodrigo & Rajapakse (2010).

  • Coastal environments: Malaria in coastal cities has been partially attributed to the colonization of shallow salt waters. Clay soils of lagoons have also been noted for collecting stagnant water, providing excellent aquatic conditions for vectors species
  • Rivers and floodplains: Rivers and their floodplains provide great breeding grounds for mosquitoes in riverside urban communities, as demonstrated by the strong association between malaria risk and proximity to a floodplain. Large fields with loamy/clay soils tend to collect stagnant water from rivers and provide optimal conditions for anopheles breeding.
  • Altitude: Altitude is commonly thought to play an important role in limiting malaria in the tropical highlands by negatively influencing the development of vector species. (Owusu-Ofori et al; 2010).

Presence of artificial vector breeding sites

It is widely regarded that artificial rather than natural vector breeding sites provide the most abundant sources of mosquito larvae in urban centres  these include water tanks, construction sites, and swimming pools

Prevention of malaria

According to Kokwaro (2009) Methods used to prevent malaria include medications, mosquito elimination and the prevention of bites. There is no vaccine for malaria. The presence of malaria in an area requires a combination of high human population density, high anopheles mosquito population density and high rates of transmission from humans to mosquitoes and from mosquitoes to humans. If any of these is lowered sufficiently, the parasite will eventually disappear from that area, as happened in North America, Europe and parts of the Middle East. However, unless the parasite is eliminated from the whole world, it could become re-established if conditions revert to a combination that favours the parasite’s reproduction. Furthermore, the cost per person of eliminating anopheles mosquitoes rises with decreasing population density, making it economically unfeasible in some areas (WHO, 2014).

Mosquito control

Mosquito control refers to methods used to decrease malaria by reducing the levels of transmission by mosquitoes. For individual protection, the most effective insect repellents are based on DEET or picaridin. Insecticide-treated mosquito nets (ITNs) and indoor residual spraying (IRS) have been shown to be highly effective in preventing malaria among children in areas where malaria is common. Prompt treatment of confirmed cases with artemisinin-based combination therapies (ACTs) may also reduce transmission (Transer, Lenger & Sharp, 2010).

Mosquito nets help keep mosquitoes away from people and reduce infection rates and transmission of malaria. Nets are not a perfect barrier and are often treated with an insecticide designed to kill the mosquito before it has time to find a way past the net. Insecticide-treated nets are estimated to be twice as effective as untreated nets and offer greater than 70% protection compared with no net. Most nets are impregnated with pyrethroids, a class of insecticides with low toxicity. They are most effective when used from dusk to dawn. It is recommended to hang a large “bed net” above the centre of a bed and either tuck the edges under the mattress or make sure it is large enough such that it touches the ground (Enayati & Hemingway, 2010).

Other methods

Community participation and health education strategies promoting awareness of malaria and the importance of control measures have been successfully used to reduce the incidence of malaria in some areas of the developing world. Recognizing the disease in the early stages can stop the disease from becoming fatal. Education can also inform people to cover over areas of stagnant, still water, such as water tanks that are ideal breeding grounds for the parasite and mosquito, thus cutting down the risk of the transmission between people. This is generally used in urban areas where there are large centres of population in a confined space and transmission would be most likely in these areas. Intermittent preventive therapy is another intervention that has been used successfully to control malaria in pregnant women and infants and in preschool children where transmission is seasonal (Meremikwu, Donegan, Sinclair, Esu & Oringanje, 2012).

Medications

There are a number of drugs that can help prevent malaria while travelling in areas where it exists. Most of these drugs are also sometimes used in treatment. Chloroquine may be used where the parasite is still sensitive. Because most Plasmodium is resistant to one or more medications, one of three medications—mefloquine (Lariam), doxycycline (available generically), or the combination of atovaquone and proguanil hydrochloride (Malarone)—is frequently needed (Jacquerioz & Croft, 2009).

The protective effect does not begin immediately, and people visiting areas where malaria exists usually start taking the drugs one to two weeks before arriving and continue taking them for four weeks after leaving (except for atovaquone/proguanil, which only needs to be started two days before and continued for seven days afterward). The use of preventative drugs is often not practical for those who live in areas where malaria exists, and their use is usually only in short-term visitors and travellers. This is due to the cost of the drugs, side effects from long-term use, and the difficulty in obtaining anti-malarial drugs outside of wealthy nations. The use of preventative drugs where malaria-bearing mosquitoes are present may encourage the development of partial resistance. An exception to this is during pregnancy when taking medication to prevent malaria has been found to improve the weight of the baby at birth and decrease the risk of anaemia in the mother (Turschner & Efferth, 2009).

Control of malaria

According to Kokwaro (2009), the following are some of the strategies for the control of malaria. Some are appropriate for individuals, while others are very useful on an area-wide or country wide basis.

  • Screening: Screening of dwellings to prevent malaria mosquitoes from entering and biting the people inside is a positive development measure. Screening of buildings also improves people’s lives in other ways, i.e. by keeping flies out of homes. Where it’s possible [i.e. buildings have four walls] to put screens on windows and screen doors on doors, it should be encouraged. Screening is a useful adjunct to use of a treated bed net or residual treatment of walls because it reduces the number of malaria mosquitoes entering and leaving the building.
  • Biological control: Mosquito fish reduce larval mosquito populations, and some countries have established programmes for distributing these small fish to residents. Mosquito fish are often particularly effective in small ponds, water tanks etc.
  • Source reduction: This is possible in some conditions but very difficult in other conditions. Source reduction is particularly useful for vector species, such as Anopheles stephensi, that often breed in man-made containers [i.e. water tanks] and at construction sites. There are several species of malaria vectors, and these species breed in many different locations. If the vector mosquitoes are breeding in water tanks, for example, it is possible to screen the tanks. However, if the malaria mosquitoes are breeding in a swamp, it is not always possible or wise to attempt to drain the swamp. Thus, other strategies for breaking transmission may need to be used.
  • Drug treatment of malaria patients: People who have malaria have parasites available for malaria mosquitoes that bite them. If they are treated with appropriate drugs, the parasites disappear from their blood and are not available to the mosquitoes. This helps to reduce the transmission of malaria.
  • Use of insect repellents: This is especially recommended for those who are travelling or are temporarily in malarias areas. This strategy is too expensive for many people who actually live in malarious areas.
  • Use of mosquito mats and coils: This is similar to the use of repellents. Some people may be allergic to the smoke that these devices emit, and for some, these devices are too expensive.
  • Use of bed nets that are treated with an insecticide: This is a strategy that has been proven to be effective in reducing childhood morbidity and mortality in numerous studies in Sub-Saharan Africa. A pyrethroid insecticide [derivative of compounds found in the flower Chrysanthemum cineraraefolium] is used to treat the bed nets. The mosquitoes that land on the net are prevented from biting the person sleeping under the net, and mosquitoes often avoid landing on the net altogether. The bed nets need to be re-treated with insecticide at intervals of approximately 6 months.
  • Residual treatment of interior walls: In many instances, malaria mosquitoes rest on the walls before or after biting people. Residual treatment of the walls inside a house repels or kills the mosquitoes. This malaria control strategy is very effective where houses have four walls. An insecticide with residual activity needs to be used so that the treatment lasts for some months. Some insecticides are more expensive than others. Also, malaria mosquitoes in some places are resistant to some insecticides. Thus, a large variety of possible insecticides need to be available for this purpose.

Conclusion

Malaria is a mosquito-borne infectious disease of humans with causes fever, fatigue, vomiting and headaches and in severe cases, it can cause yellow skin, seizures, coma or death. The prevalence of malaria in an area is caused mainly by environmental factors such as the presence of natural and artificial breeding sites.

Recommendations

To effectively and efficiently control malaria, factors responsible for its transmission must be eliminated or reduced to its barest minimum through the following measures:

  • Screening of dwellings to prevent malaria mosquitoes from entering and biting the people inside
  • Biological Control
  • Source Reduction
  • Drug treatment of malaria patients
  • Use of insect repellents
  • Use of mosquito mats and coils
  • Use of bed nets that are treated with an insecticide
  • Residual treatment of interior walls

References

Caraballo, H. (2014). “Emergency department management of mosquito-borne illness: Malaria, dengue, and West Nile virus”. Emergency Medicine Practice 16 (5). 61-63.

Enayati, A. & Hemingway, J. (2010). “Malaria management: Past, present, and future”. Annual Review of Entomology 55, 569–91.

Fairhurst, R. M. & Wellems, T. E. (2010). “Plasmodium species (malaria)”. Pennsylvania: Churchill Livingstone/Elsevier. pp. 3437–62.

Fernando, S.D., Rodrigo, C. & Rajapakse, S. (2010). “The ‘hidden’ burden of malaria: Cognitive impairment following infection”. Malaria Journal 9, 366.

Jacquerioz, F.A. & Croft, A.M. (2009). “Drugs for preventing malaria in travellers”. Cochrane Database of Systematic Reviews (4), CD006491

Kokwaro G (2009). “Ongoing challenges in the management of malaria”. Malaria Journal 8 (Suppl 1), S2.

Meremikwu, M. M., Donegan, S., Sinclair, D., Esu, E. & Oringanje, C. (2012). “Intermittent preventive treatment for malaria in children living in areas with seasonal transmission”. Cochrane Database of Systematic Reviews 2 (2), CD003756.

Mueller, I., Zimmerman, P. A. & Reeder, J.C. (2007). “Plasmodium malariae and Plasmodium ovale—the “bashful” malaria parasites”. Trends in Parasitology 23 (6), 278–83

Owusu-Ofori, A. K., Parry, C. & Bates, I. (2010). “Transfusion-transmitted malaria in countries where malaria is endemic: A review of the literature from sub-Saharan Africa”. Clinical Infectious Diseases 51 (10), 1192–8.

Tanser, F.C., Lengeler, C. & Sharp, B.L. (2010). Lengeler, Christian, ed. “Indoor residual spraying for preventing malaria”. Cochrane Database of Systematic Reviews (4), CD006657

Turschner, S. & Efferth, T. (2009). “Drug resistance in Plasmodium: Natural products in the fight against malaria”. Mini Reviews in Medicinal Chemistry 9 (2): 206–14.

WHO (2014). World Malaria Report 2014. Geneva, Switzerland: World Health Organization. pp. 32–42.

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