Vector Borne Diseases

Introduction

In principle, all vector borne diseases are a serious threat to children's health. Some, however, pose a specific threat to children, because a child's immune system is unable to cope with the assault by the infectious agent, or because the way a child behaves may increase vulnerability to disease. These diseases include: Malaria, Lymphatic filariasis, Japanese Encephalitis (JE), Dengue Fever and Leishmaniasis.

Malaria, which is transmitted by a mosquito, overwhelmingly kills children. Malaria is a major public health problem in South-East Asia Region, which reports about 3 million cases and 30,000 deaths annually. Lymphatic filariasis is an infection of parasitic worms lodging in the lymphatic system. The decrease in healthy life years caused by this disease is second only in its magnitude to malaria.

Japanese encephalitis is found in the irrigated rice production systems of South and South-East Asia. JE often causes nervous disorders and a life-long debility in the afflicted patient. An average of 40,000 clinical cases are estimated to occur each year, with a case fatality rate of 20%. Of the survivors, 50% are affected mentally for life.

Dengue fever also affects young children disproportionately in high burden countries. The disease's most lethal form, dengue haemorrhagic fever, kills, on average, over 10,000 children each year. During major outbreaks, children's hospitals can come to a grinding halt as wards are overwhelmed by admissions.

Leishmaniasis, a parasitic disease transmitted by sandflies, manifests itself either as skin lesions or as damage to internal organs - the latter form (called Kala azar) is life-threatening with an estimated 59,000 deaths in 2001. Every year an estimated 2 million cases of cutaneous leishmaniasis occur, and an estimated 95% of patients are children under 5.

Mosquitoes that transmit diseases in the countries of the South-East Asia Region belong to genera Anopheles, Culex (house mosquito), Aedes (Asian tiger mosquitoe) and Mansonia. Many species of Anopheles transmit malaria from one person to another. Anopheles mosquitoes breed in clean water and females bite indoors and outdoors. The mosquito Aedes aegypti transmits dengue and dengue haemorrhagic fever (DHF). Aedes breeds in clean water stored in various man-made receptacles, pots, tanks, desert room coolers, flower vases, rainwater trapped in disused tyres and metal scrap. Aedes is mainly a day-biter and a split-biter (a single female tends to bite many persons until fully fed with blood).

Dengue/DHF outbreaks occur in urban/semi-urban areas, but also in villages following water storage practices. Culex mosquitoes transmit lymphatic filariasis and Japanese encephalitis. They breed in clean as well as polluted waters Mansonia mosquitoes transmit another form of filariasis. They breed in water bodies infested with floating vegetation.

Sandflies cause itching on bite and transmit leishmaniasis from an infected person to another. Sandflies breed in damp and sheltered soils often at the base of walls, in damp cracks, in soil contaminated by animals and in the burrows of rats, gerbils and ground squirrels about 50 metres around human habitations.

Impact on the health of children

Although malaria affects people of all ages, children in general and underprivileged children living in socio-economically deprived conditions in particular are at a greater risk. Malaria is one of the major causes of childhood anaemia and spleen enlargement. It decreases cognitive abilities in children and is considered an important cause of school absenteeism. Malaria during pregnancy can lead to lowbirth weight babies. Unprotected children and those going to bed early become more prone to mosquito bites in the early night-hours. Itching caused by mosquito bites can cause sleep disturbances.

Children who spend considerable time in schools, playgrounds and parks located in areas with plenty of surface water are prone to infective mosquito bites. Day-biting and split biting habits of Aedes mosquitoes put the schoolchildren at a greater risk of getting Dengue fever.

Untreated infection with worms of filariasis during childhood can lead to development of elephantiasis (swollen legs, like an elephant), typical deformations caused by "lymphedema" and "hydrocoele" in children as young as 12. It can become a cause of social stigma affecting people of all ages including children.

Outbreaks of JE particularly affect children under five (about 90 per cent of cases); JE also affects people of all ages and can mentally cripple the affected person for life.

Kala azar is a major cause of liver and spleen enlargement in affected children in endemic areas. It can lead to death if untreated.

Suggested action to protect children against vector borne diseases:

As children usually go to bed earlier than adults, when mosquitoes become active, the use of insecticide treated mosquito nets and the screening of windows, doors and eaves provide a very effective means of protecting them against malaria.
General environmental management, including improved water management in irrigated areas, placing cattle strategically between breeding places and homesteads, and drainage or filling of water collections, may help reduce transmission risks.
Combined irrigated rice production and pig rearing close to housing must be avoided to break the Japanese encephalitis cycle.
Hygiene education and designated safe places to swim as well as other environmentally sound measures will reduce the transmission risks of some parasite-transmitted disease and help control morbidity.
Breeding of mosquitoes in the house can be prevented by keeping water storage containers fully covered, and periodically emptying and drying outvarious containers that retain water including buckets, discarded food containers, drums, flower vases, and car tires (where water can collect). This will help reduce dengue transmission risks.

Success stories

Changing the Crop Patterns: Changing the crop patterns helped Indonesia in controlling malaria-causing vectors. Synchronization of rice culture, uniform quality of seed, regulation of the sowing time and harvesting of early-maturing variety contributed to vector control. Crop rotation was encouraged, and the farmers were asked to sow a non rice crop after two rice crops. These practices led to enhanced rice productivity and controlled the malaria vector Anopheles aconitus. Prawn and fish cultures were further encouraged in the coastal areas with high water salinity. This controlled the breeding of Anopheles sundaicus and became an effective malaria control tool. These practices had the dual benefit of disease control and increase in income and productivity, once again proving the importance of intersectoral collaboration.

Source : WHO INFO

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