TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE! (1999) 93,458-459

Malaria control: bednets or spraying?

Malaria control in the Afghan refugee camps of western Pakistan

Mark Rowland HealthNet International, I? 0. Box 889, Peshawar, Pakistan; and London School of Hygiene and Tropical Medicine, London WClE 7HT, UK

Keywords: malaria, disease control, insecticides, house spraying, bednets, malathion, permethrin, refugees, Pakistan

As a result of the Soviet invasion of Afghanistan, over 3 million Afghan refugees crossed into Pakistan during the early 1980s. The refugees were settled in 340 camps in the 2 western provinces of Balochistan and North West Frontier Province. Because of the protracted civil war, about 40% still remain in Pakistan. The camps were sited on marginal land that was often either waterlogged or adjoining rice cultivation. Malaria became a significant problem in this non-immune population (SULEMAN, 1988), and at its height in the early 1990s over 150 000 cases were being diagnosed and treated each year by the medical services run by the United Nations High Com- missioner for Refugees (UNHCR) and the Government of Pakistan. Twenty-five percent of cases were due to falciparum malaria and 75% were due to vivax.

As a general rule UNHCR adopts the same health policies and practices as the host country. In Pakistan indoor spraying with residual insecticide has been the mainstay of malaria control since the eradication era of the 1950s and 1960s. UNHCR initiated spraying cam- paigns in the camps (by now, villages of mud houses) using malathion, the insecticide favoured by national health authorities, despite evidence of widespread resis- tance in 1 of the vectors, Anopheles stephensi (RATHOR et al., 1985). By 1991 the campaign had grown to cover about one-third of the camps and 1.1 million refugees each year. Despite the recurrent high annual expenditure on insecticide UNHCR was hesitant to evaluate the campaign’s effectiveness by undertaking randomized controlled trials as there was an understandable reluc- tance to withhold assistance to any particular group or to do anything that might be misconstrued as an experiment on refugees. However, comparative trials either with different insecticides or with spraying campaigns held in different months were considered acceptable and necessary.

The annual spraying campaign is normally held in late July to coincide with the monsoon rains. Anophelines positive for malaria circumsporozoite protein are found in all months of the year, but mosquitoes generally show the first increase in biting density in May. Since this coincides with the seasonal increase in vivax cases, it was considered that a spraying campaign held in spring might stand a better chance of controlling vivax malaria than one held in summer (ROWLAND et aZ., 1997a). Twelve refugee villages were paired to receive a spraying in either Auril or lulv. Each of the villages had a well-utilized basic health &if (BHU) run by-either UNHCR or non- governmental organizations (NGOs) that provided free malaria diagnostic and treatment services. The criteria for pairing villages was a similarity in the pre-intervention year’s annual incidence rate or parasite index (the num- ber of cases per 1000 population per year diagnosed by microscopy at the BHU). Incidence in the year after spraying was the main indicator for evaluating impact. The geometric mean annual incidence rate fell from 56 to 42 inthe group sprayed in April and from 54 to 20 in the mouu soraved in Tulv. The orotective efficacv (PE) of me July spraying”over the April spraying (calculated from the mean and standard error of the log rate ratio of eachpair) wascalculated to be 51% (95% CI 14%, 72%). Although the insecticide was clearly effective in control- ling vivax malaria, bioassays confirmed that residual activity was insufficient to extend from the spring to the main transmission season that came after the monsoon.

In retrospect, most of the vivax cases observed in the spring were probably the result of relapsed infections from the previous autumn rather than of new transmis- sion(Fox& STRICKLAND, 1989).

As the phrase suggests, insecticide spraying campaigns can be likened to military campaigns. Strategy is defined by experts according to strict criteria, planning requires a regular flow of high quality (epidemiological surveil- lance) information from the periphery to the centre, the window of opportunity may be a narrow one (July/ August spraying), success may depend on logistic effi- ciency and supply routes that ensure product (insect- icide) delivery whenever and wherever needed, efforts must be maintained despite conflicting pressures on the health budget from political masters if success is to be achieved, those on the front line or the beneficiaries have little say in the strategy.

Put like this, it is no wonder that the eradication effort collapsed in Asia after 20 years of struggle. But oddly, after several years of growth and development, the UNHCR health programme in Pakistan was well adapted to this approach. Each camp had a well-stocked BHU (with vehicle), there was 1 well-equipped labora- tory serving every 3 BHUs, each well-trained technician could diagnose malaria with 98% accuracy, and monthly quality control of microscopy ensured accurate surveil- lance information that formed a basis for prioritizing camps for vector control. But even the best campaigns rarely run smoothly and spraying programmes are no exception to this. Imported insecticide may be held up in customs, the budget for spray labour may be overlooked, insecticide may be sent to the wrong camp. Each year about a quarter of the camps on the spray list were never sprayed. The rather arbitrary criteria for spraying a camp was that more than 3% of the population should have been diagnosed as vivax positive or more than 1% as falciparum positive in the previous year. Some camps below the vivax threshold were sprayed because they exceeded the falciparum threshold, and vice versa.

For these reasons it was possible to conduct a series of retrospective studies in which 20-30 unsprayed camps could be matched blindly with sprayed camps that had similar pre-intervention incidence rates, population sizes, and geographical proximity. Protective efficacies were calculated as outlined above for the spring/summer spray trial comparison. Using this methodology the PE of malathion spraying against &ax malaria wascalculated to be 37% in 1991 and 44% in 1992. results not significantly different from those of the prospective spring/summer spray trial. The PE against falciparum malaria was 56% in 1991 and 49% in 1992. PE was always lower against vivax malaria because vector control cannot, of course, prevent relapses in the intervention group. By applying this methodology to all camps, it is estimated that the UNHCR spraying campaigns in Frontier Province averted 19 000 cases of falciparum and 68000 cases of vivax malaria between 1991 and 1995; as a proportion this represents 22% of the cases diagnosed and treated during that period.

Vertically managed spraying programmes may be an appropriate response to malaria problems in temporary refugee camps or when the health system is well struc- tured, but they are anathema to advocates of primary health care, and when international aid declines any gains made may be quickly lost. In Afghanistan, where

MALARIA CONTROL: BEDNETS OR SPRAYING? 459

the health structure was destroyed by the war, a policy based on provision of personal protection seemed the only sensible way forward. Although there was little tradition of using bednets in Afghanistan, a field trial carried out in refugee camps in- Pakistan in 1991 by HealthNet International showed that most Afghans were ready to adopt the technique and that treat‘ent with permethrin could give up to 61% protection against falcipamm and 42% protection against vivax malaria (the trial was undertaken in refugee camps rather than in Afghanistan itself for security reasons) (ROWLAND et al., 1996). The trial involved giving treated nets to 10% of the community while a further 10% served as a control group. Incidence rates were particularly high in the year of the trial and indoor spraying campaigns had to be resumed afterwards to protect the majority who lacked nets. Bednet coverage was increased to 30% in 1992. By 1994 the dual control strategy had caused incidence to fall by almost 90% to only 78 cases per 1000 per annum, while in unsprayed camps incidence fell by only 15% (ROWLAND et al., 1997a, 1997b). A case-control study was undertaken in 1994 to see whether Afghans were still using the nets to good effect despite the reduced transmission rates. Patients presenting at the BHUs with symptoms of malaria and who were slide positive were taken to be cases, while patients with symptoms of malaria but with a negative slide were taken as controls. By comparing cases with controls we calculated odds ratios for protection by bednets. The PE was 6 1% against falciparum and 52% against vivax malaria (ROWLAND et al., 1997b). These values were almost identical to those of the prospective trial of 1991 and suggest that PE of treated nets may be similar at high and low levels of transmission.

The level of protection obtained from treated nets in 199 1 and 1994 was not significantly different from that of the indoor spraying campaigns with malathion held in the same 2 years in and around the same district. Indoor spraying does not require a change in sleeping habits and provides passive protection to everyone in the camp. Use of nets requires self-discipline and those who claimed to use them (and 70% did) obtained an extra 10% of protection (ROWLAND et al., 1996, 1997b). Interest- ingly, the adoption of the pyrethroid lambda cyhalothrin by the UNHCR indoor spraying programme gave a similar degree (10%) of extra protection over malathion (ROWLAND et aZ., 1994). In short there is nothing to choose between indoor spraying and treated nets in terms of efficacy.

On the basis of these encouraging results a major programme of selling treated nets was started in Afghani- ita< by a consortium of NGOs coordinated by Health- Net International with sunnort from WHO and UNHCR.

II

To help define the future strategy in Pakistan and Afghanistan, a health economics analysis was under- takhn of the bednet trial and indoor spraying programme CL. Guinness. unoublished reoort). The total cost of the

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spraying programme in North West Frontier Province from 1990 to 1995 was USS2.2 million. Insecticide cost $1.1 million, nearly half of all vector control costs. The annual cost per person protected by the indoor spraying progamme was $0.63. The cost per malaria infection averted was $20, which compared favourably with that of other malaria control programmes (MILLS, 199 1).

In the bednet project from 199 1 to 1994, only 18% of costs went on insecticide while 47% went on nets (this

calculation assumes a life-span of 7 years for nets). The annual cost per person protected was $1.5 1. If the cost of nets could be placed entirely on the user, the annual cost for the programme would be $0.70 per person protected which is still no cheaper than the indoor spraying programme. But prices of nets have fallen by a quarter since 1994 and new pyrethroids such as deltamethrin are half the price of the permethrin used in the efficacy study. The spraying programme also benefited from economies of scale while the bednet project was a research trial with high monitoring costs. A full-scale bednet development project, integrated into the health system, would be more cost-effective, especially if the community were to pro- vide volunteer labour.

One should also consider the social arguments. As malaria declined in the camps the spraying programme, like any control programme, became less cost-effective and harder to justify or sustain. Many refugees are willing to pay for something tangible like a bednet (ROWLAND et al., 1997b) but few would pay for something as ephem- eral as having their house sprayed (results of unpublished surveys). A switch from spraying to nets in central and south Asia may not reap any economic benefits to control programmes, but it would encourage self-reliance and may not require the maintenance of a sophisticated delivery system or be so dependent on international aid as indoor spraying campaigns.

Acknowledgements HealthNet International’s Malaria Control Programme is

supported by the European Commission, the United Nations High Commissioner for Refueees. the WHO/UNDP/World Baik Special Programme for RGea&h and Training in Tropical Diseases (Project ID: 960662), the Department for Interna- tional Development of the UK, and HealthNet International.

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Received 27Janua y 1999; revised 28 May 1999; accepted for publication I OJune 1999