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Photo of David Le Sueur Fighting Malaria

Although South African health authorities once considered malaria intensively controlled, this story profiles David Le Sueur who explains why malaria has emerged again as the biggest threat to human health in the developing world. Following the premier of the Scientific American Frontiers Special Science Safari, David Le Sueur answered viewers' questions as part of an Ask the Scientists panel. Here are viewers' questions and his answers:



Q If malaria is carried by mosquitoes, is there any way for these infected mosquitoes to come to the U.S.? If so, is America prepared for such an outbreak that could occur from this?

A Malaria historically occurred in the USA in the southern States but was eradicated. Occasional cases are however still recorded. However malaria was never a major problem in the US. The classic example of such an importation of malaria mosquitoes was the so called "Invasion of Brazil by Anopheles gambiae" an African malaria vector in the 1930's. This resulted in severe epidemics and loss of life. This invasive mosquito was eventually eradicated but at massive financial cost and effort. The programme was funded by Rockefeller foundation and a very interesting book reporting this was published. The mosquitoes were thought to have been introduced by a ship travelling from the West Coast of Africa. The US however is a country with massive financial resources and expertise and as pointed out by a US colleague (Dr Peter Bloland) from the Centre for Disease Control (malaria division) Atlanta " in the US one case of malaria is considered a epidemic". I would suggest that for further details as to the type of precautionary measures practised, you should contact CDC.





Q Can you give us an update on the use of the GPS system since the show was filmed? Is it being used to help bring electricity and other services to this remote area?

A Yes...this is the exciting part about Geographic Information Systems of this nature, i.e. that much of the spatial data needed in health has broad application in other development sectors. Approximately 14 water supply projects are using the database, decisions to upgrade infrastructure such as roads etc. are also accessing the GIS platform. There are many other examples as well such as the planning of a development corridor between South Africa and Mozambique and once again those responsible for the feasibility study are using our malaria database for part of the plan. In many cases the availability of this data has meant that it will get many of the services planned under the South African Reconstruction and Development Programme first as the data facilitates more rapid implementation.





Q I am curious about the resistance that mosquitoes are acquiring to insecticides. Does this resistance mean that you are starting to lose ground in the fight against malaria?

A We do not have any insecticide resistance in South Africa as yet...but we do have drug resistance and this has impacted on both the cost and efficiency of control activities. However from a global perspective (especially in India) insecticide resistance is severely impacting on control efforts and contributing to a resurgence of the disease. Resistance is often associated with a change to a more expensive alternative, something which can be ill-afforded in countries where only a few dollars are available for health care per person per year.





Q Currently, is bicycle travel the sole means of reaching those in the rural areas of South Africa in the fight against malaria? Or are there some health care facilities located in the rural areas where the families may been seen instead of waiting for the mobile unit?

A No, There are a lot of clinics compared to most other African countries, but the number is inadequate. The new government has a large initiative which is building almost 50 additional rural clinics per year. The aim of the active surveillance on bicycles is to get to people before they get ill and need to report to the clinic. In addition, it needs to be borne in mind that diagnostic facilities (microscopes etc.) do not exist at many of these clinics which are Primary Health Care facilities and which refer more complicated issues to the district hospital.

To improve this diagnostic process and the time lag between diagnosis and treatment, microscopes and screeners are know being placed at the clinics in the high-risk areas during the transmission season. There are now new diagnostic tests which are dipstick/reagents test + a spot of blood. These can be used in almost any setting and do not need a high level of skill to apply. However, they are quite costly for most African countries' pockets ($1.50 per test). This needs to be viewed in terms of many countries only having a few dollars per head to spend on all aspects of health care for a single person. The dipsticks are know being used extensively by the surveillance agents in South Africa.

We also have mobile clinics which visit certain points once a week and doctors fly to each clinic once a week. There is also ambulance service between the clinic and the hospitals; however, this is inadequate to meet current demands.





Q Have mosquitoes been affiliated with transmitting other diseases?

A Yes, disease like Japanese enchaphilitis and many Arboviruses (viruses which usually occur in other animals). Some examples of these are Dengue Hameoraghic, fever, West Nile, Chikungunya. Other disease are Yellow fever and Filariasis (Wucheria Bancroftii), which causes Elephantitis.





Q Are there researchers searching for a vaccine for malaria, or is all time and money spent on prevention?

A No, Millions of dollars are spent annually on vaccine research in the USA alone. However, the malaria parasite is a very complex one and despite more than 20 years of intensive research we are still at least a decade away from an effective vaccine. Recently hopes were raised with a synthetic peptide vaccine called SPf66. This was developed in Colombia and many were skeptical about it, especially as it was coming from a third world country. Subsequent trials have shown that it is not as effective as originally claimed, but that it by far the best candidate vaccine produced to date. Efforts are currently underway to refine this.





Q Can a pregnant woman spread malaria to her fetus?

A This only occurs if the mechanical barrier offered by the placenta is damaged in some way, as may occur at birth. However of far greater risk is that severe malaria occludes the capillaries and places the pregnant women at high risk for abortive pregnancy. This is a very common in endemic malaria areas of Africa.





Q My mother is from South Africa and we try to go every two years. One year we went camping in Sun City. Everyone got bit by so many mosquitoes. I was just wondering what the chances were of us getting malaria?

A Malaria used to exist in areas such as Sun City, Pretoria, Johannesburg and as far south as Port St. Johns. In the 1930's severe epidemics occurred which eliminated over 2% of the province of KwaZulu-Natal (22,000 deaths, population 985,000). However, malaria control has been extremely successful and the KZN Province has more than 400 people dedicated to malaria control alone. These efforts at a national level have pushed back the boundaries of malaria to the borders of our neighbouring countries. Much of our malaria is as a result of importation via migrants from Mozambique where control is only just starting to be re-established after the end of the civil war. There are in excess of 600 species of mosquitoes in South Africa and only one of these is a major vector, so many of the mosquitoes are of nuisance value alone.

For further details visit our website at www.malaria.org which has malaria maps, seasonality profiles as well as links to the Centre for Disease Control, USA. This site is under construction and we will soon add other advice about mosquito nets, repellents, mosquito behaviour, drug resistance. In the meantime we list various telephone numbers for advice. Due to overseas demand we will update this with fax numbers as well.

A few pointers: 1. Remember the malaria vector only bites at night so repellent should be applied before sunset. 2. If you are staying in a chalet, close all mosquito screens before sunset and use the airconditioning. 3. Consider carrying an insecticide-impregnated mosquito net especially if you are going to rural areas or camping. 4. Make use of repellent and apply these before dark. Make use of mosquito coils in your accommodation. 5. Enquire about what is the most suitable drug to take for where you are going; i.e., is there drug resistance and if yes to what drug. 6. Are you going in the high risk period (seasonal malaria areas)? 7. Always start the drug a week before you leave so that if you are going somewhere remote and react adversely, you have the chance to change to an alternative drug. These alternatives may not be available where you're going. 8. Continue with the drug dosage at least 4 weeks after leaving a malaria area. 9. Remember no drug is 100% effective so if you get ill after being in a malarious area, mention to your doctor that you have been in such an area. 10. Malaria carries a high risk of foetal loss in pregnant women. However, there are certain drugs which may be used during pregnancy.

Adhere to all of the above and travel freely anywhere!





Q Why doesn't the malaria kill the mosquitoes?

A There is evidence that the malaria parasite may adversely affect the mosquito. However, one has to bear in mind that the parasite needs the mosquito to survive. The parasite has a cycle both in man and the mosquito and these are what complete the life-cycle. Thus if it killed every mosquito it infected....it would literally kill itself as it needs the mosquito to "carry it" to the human host. Once the human host is infected then it infects the next mosquito that bites her/him......and so the cycle goes. Thus the very definition of a parasite is something which parasitises its host and does not kill it outright, i.e. uses the host to serve its own ends!

However, not all mosquitoes carry malaria as some are resistant to the parasite. Thus the malaria parasite, man and the mosquito represent a finely balanced ecological circle which has severe consequences for man. It is this complexity of the parasite and its numerous stages of development which complicate the production of a malaria vaccine.





Q What happens when you get malaria? How does it affect your body and cause death?

A The malaria mosquito injects sporozoite when it bites you. These reside in the salivary glands of the mosquito which produces the anti-coagulant which enables the mosquito to draw blood. Once in the blood the sporozoites infect your red blood cells. The parasite then goes through a high cycle in your blood (rings, trophozoites, schizonts) and some of these develop into sexual forms (male and female) known as gametocytes. If a mosquito takes a blood meal containing these then they become infected. In the meantime an increasing number of the red blood cells of the patient are becoming infected with malaria. This results in symptoms such as fever, headaches, rigors (severe shaking), nausea, diarrhoea. If the disease progresses to its more severe stage then a number of complications may occur. Firstly as the red blood cells are infected and the parasite develops, the RBC are destroyed and anaemia may result. Renal failure (kidneys) may also occur. Many cases in their advanced form result in cerebral malaria. This is due to the occlusion (blocking) of venous (blood) supply in the brain. Similar blockage in the placenta of a pregnant woman results in foetal loss.

The blocking occurs due to the fact that the infected RBC seem to have an affinity for each other and "raft together" and these then are large enough to obstruct capillaries, etc.





Q How are people, who are infected with the malaria parasite, cured? What medications are used in the treatment?

A The malaria mosquito injects sporozoite when it bites you. These reside in the salivary glands of the mosquito which produces the anti-coagulant which enables the mosquito to draw blood. Once in the blood the sporozoites infect your red blood cells. The parasite then goes through a high cycle in your blood (rings, trophozoites, schizonts) and some of these develop into sexual forms (male and female) known as gametocytes. If a mosquito takes a blood meal containing these then they become infected. In the meantime an increasing number of the red blood cells of the patient are becoming infected with malaria. This results in symptoms such as fever, headaches, rigors (severe shaking), nausea, diarrhoea. If the disease progresses to its more severe stage then a number of complications may occur. Firstly as the red blood cells are infected and the parasite develops, the RBC are destroyed and anaemia may result. Renal failure (kidneys) may also occur. Many cases in their advanced form result in cerebral malaria. This is due to the occlusion (blocking) of venous (blood) supply in the brain. Similar blockage in the placenta of a pregnant woman results in foetal loss.

The blocking occurs due to the fact that the infected RBC seem to have an affinity for each other and "raft together" and these then are large enough to obstruct capillaries, etc.





Q How are people, who are infected with the malaria parasite, cured? What medications are used in the treatment?

A They are cured by using drugs which eliminate the parasite from the body. There are many of these, but the situation has been compromised by the development of multiple drug resistance. This is especially the case in S.E. Asia where virtually none of the prophylactic (preventative) drugs work. Drugs such as chloroquine were cheap, had few side effects and were effective in both the treatment and prevention of malaria. In 1978 chloroquine resistance arrived in Africa and now it covers the whole continent. Unfortunately many of the alternatives are more expensive and have greater side-effects. Thus for the traveller from the West who can afford the right drugs it is not really a major problem, but for the rural poor of Africa it is.

Some medications used are: Fansidar-sulphadoxine/pyremtehamine Hafan-Halofantrine Lariam-Mefloquine Quinine

The last is the oldest and still the most widely effective. It was derived from the choncona tree in South America and was discovered by Jesuit monks. Its discovery was a powerful tool in their hands as it was kept secret and enabled them to effectively colonise malaria areas.





Q In the United States several of the effects of DDT have been well documented. The California Brown Pelican, for example, was driven to near extinction as a result of egg shell thinning known to be caused by ingestion of DDT laden fish. Have studies been done to determine the levels of DDT in various sectors of the South African ecosystem? Are there currently any fauna threatened by the accumulation of DDT in their tissues? Considering the fact that DDT is amplified through the food chain, are there concerns and studies being conducted on the effects of spraying on the human population? And lastly, which specific pesticide is currently being employed to fight the mosquito?

A DDT is still recommended by the World Health organisation. The DDT debate is still a debate and much of the egg shell thinning attributed to DDT, some would say was a result of Polychlorinated-biphenyls (PCB's), used to stabilise transmission oil. Old oil was often used on ash roads to keep down the dust. However the DDT saga rages on, with books such as the DDT Myth. There is no doubt that the DDT issue has been clouded by emotion and in some cases it has been replaced by far more acutely toxic alternatives.

I started my life as a Conservationist after having done a BSc Honours degree on the population dynamics of the Southern Reedbuck at Lake Stlucia Reserve. This has obviously had a strong influence on my thoughts on the matter.

I thus started a project in 1980, to assess the impact of spraying with DDT in our malarious areas. A PhD student, Henk Bouwmann, headed up this work. We looked at a number of things: Levels in mud sediments of lakes in the area. Levels in birds such as the Pied Kingfisher Level in the blood of spraymen Level in the breast milk of mothers.

The levels reached in the environment (mud and birds) were not cause for concern. It should be remembered that the levels used in malaria control are a fraction of that used in agriculture and it is sprayed inside houses. Thus environmental contamination is reduced.

The levels in the serum of spraymen varied from acceptable to unacceptable and more stringent safety procedures were brought into place.

The levels in mother breast milk were of great concern as they were 30x the allowed daily intake (ADI) for primiparous mothers (first child). The reason is that DDT and its products DDD/DDE accumulate in body fat and this is mobilised by the lactating mothers. The levels were such that they could result in a hyporeflexia in the breastfeeding infant. It is not clear that this would be the case but the risk was there and the impact of this on the long term development of the child would be difficult to assess. The cost of carrying out such a study was more than our entire malaria research budget and we could thus not do the study.

However at this stage we had noted a number of other problems with DDT: The mosquito seemed to be behaviourally avoiding contact with it and wherever it was sprayed there was an increase in bedbug, which are resistant, but there predators are not. Thus the biological control of these was removed, populations boomed and houses became uninhabitable. This lead to resistance to control activities.

We thus started a fast track programme on assessing synthetic pyrethroids as alternatives. These are totally biodegradable. But we ran into problems as many of them did not seem to last the six months required to protect the people, when sprayed on the mud walls. We thus had to collect lots of mud samples from malaria areas, apply different pyrethroids and different formulations at different concentrations to find a suitable alternative. Once again cost was an issue as these are more expensive. We found one but wanted two so that the commercial company with the one alternative would have some competition and the price would be kept in check. This we did and last year this province changed to a bio-degradable alternative. This year the second province is changing and that will leave one more province using DDT. This is however unlikely to occur in the following year. This work has had great regional impact as many of our neighbours do not have the capacity to do such work and thus look to us. The majority of the countries in the region are likely to follow suite.

However, it's not all plain sailing as pyrethroids are colourless and thus it is far more difficult to quality-control their application. This lack of colour has advantages as means that furniture and other surfaces can be sprayed. Various possibilities are now been evaluated such as the addition of a fluorescent dye, so that application can be checked with a UV torch.




 

Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.