Lessons from Zanzibar: How the isles beat malaria

For Mwashamba Idi and Juma Ali Juma, both residents of Zanzibar Island, malaria is not a common part of their disease vocabulary.

Matter-of-fact, malaria, a disease that kills a child every two minutes, is unheard of among many residents of the Unguja (Zanzibar Island) of whom have either never had the infection before, or not for a long time. This is because the Island has managed to reduce its prevalence of malaria to below one percent, meaning that extremely few people, mostly travellers and migrant workers test positive for the mosquito-borne disease.

Using a variety of strategies like annual indoor/outdoor residual spraying, the revolutionary government of Zanzibar, a semi-autonomous government within Tanzania has been able to keep malaria-transmitting mosquitoes at bay. Zanzibar is made up of a series of islands in the Indian Ocean off the coast of Tanzania, where until 2003, the transmission of malaria was more common. Over the last two decades, however, the island has maintained malaria prevalence below one percent.

In 2020, an estimated 627,000 people died of malaria—most were young children in sub-Saharan Africa. According to the latest World Health Organisation’s (WHO) World Malaria report, there were an estimated 241 million malaria cases worldwide in 2020.

Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. It occurs mostly in poor tropical and subtropical areas of the world. In many of the countries affected by malaria, it is a leading cause of illness and death.

In areas with high transmission, the most vulnerable groups are young children, who have not developed immunity to malaria yet, and pregnant women, whose immunity has been decreased by pregnancy. The mosquito-borne disease is among the five leading causes of death in children under five years, including pre-term birth complications, pneumonia, birth asphyxia, and diarrhoea.

According to the Zanzibar Malaria Elimination Programme (Zamep), the island aims to eliminate malaria by 2023.

Science, in the form of mass indoor spraying; provision of insecticide-treated mosquito nets; community sensitisation; coordinated international effort and investment, including early detection and treatment interventions that have quelled Plasmodium falciparum, the deadliest malaria parasite globally and the most prevalent in Africa— have all combined to deliver the miracle of low malaria transmission in Zanzibar.

These interventions, with sustained high-community uptake, have been temporally associated with a major malaria decline, most pronounced between 2004 and 2007 and followed by a sustained state of low transmission.

“Initially, the methods for diagnosing malaria were less accurate and not always available back then. So children with fever were commonly treated as if they had malaria,” recounts Mohamed Ali, the programme manager at Zamep.

The most crucial lesson the team at Zamep has learned is that targeting malaria interventions effectively is critical and should be informed by consistency. Between 2005 and 2012, Zamep’s deputy programme Faiza Bwanakheri Abbas explains, Zanzibar began a mass combination of interventions including the use of artemisinin-based combination therapy (ACT) for malaria treatment and indoor/outdoor residual spraying to reduce mosquito-breeding areas, insecticide-treated mosquito nets for malaria prevention, combined with community education which made a significant impact.

“In 2005, we introduced Artemisinin-based combination therapy (ACTs). A year later we introduced blanket indoor spraying followed by mass campaigns for use of bed nets. What has enabled us to maintain the numbers has been a surveillance system we introduced in 2008 for weekly detection of the patterns of malaria transmission, which was followed by a malaria case notification system introduced in 2012 where every case was followed from point of detection to their home to figure out the source of transmission and whether there were more people infected,” explains Ms Abbas. “This meant that by 2013, any resident of Zanzibar suspected to be infected with malaria was followed up, tested, and put on treatment early enough. The use of rapid diagnostic tests (RDTs) allow trained community members to perform malaria diagnosis accurately and prescribe appropriate treatment, reducing as much as possible, any delay between the onset of fever and treatment,” notes Fredros Okumu, director of science at the Ifakara Health Institute (IHI) in Tanzania.

The island’s roll-out of community-based interventions free of charge helped cut new cases of malaria recorded in the island’s health facilities by 94 percent between 2003 and 2015. Today, Zanzibar provides a basic public health service package for its residents like Ms Mwashamba and Mr Juma free of charge. As part of this package, all people on the island have access to affordable services for the diagnosis and treatment of malaria, regardless of their status.

“We ensured that there was universal coverage of testing and treatment was standardised and of quality regardless of whether the person received treatment in a public or private health facility,” adds Ms Abbas.

She also says that vector control strategies are not only dynamic but are also informed by the mosquito behaviour, trends, and response to the repellents used. Vector control is any method to limit or eradicate the insects which transmit disease pathogens. The most frequent type of vector control is mosquito control. Finally, Ms Abbas adds, tracking insecticide and drug resistance is key and for that reason, the Zanzibar malaria elimination programme also hosts an insectary for the rearing of living mosquitoes to track resistance before it occurs.

Insecticide-based interventions have averted more than 500 million malaria cases since 2000, but insecticide resistance in mosquitoes could bring about a rebound in disease and mortality. Malaria treatment efforts are hindered by the rapid emergence and spread of drug-resistant parasites. In recent years, reports of sporadic resistance to modern malaria drugs began appearing, and are now confirmed in Rwanda and Uganda.

“Just like human beings, mosquitoes have a behavioural pattern which we monitor to determine the type of intervention strategy we need to deploy at any particular time,” Ms Abbas notes.

Resistance occurs when the effectiveness of a drug is reduced and it no longer provides a full cure against the targeted infection. In Africa, most malaria-infected people who receive treatment in good time are fully cured and suffer no long-term effects. Front-line drugs remain largely effective, but the likelihood of widespread failure is growing fast, notes Dr Okumu.

Simple analysis to monitor parasite drug response in direct patient samples can detect drug resistance before it becomes clinically apparent, and can inform changes in treatment policy to prevent the spread of resistance.

A 2019 study published in BMC Medicine indicates that Zanzibar represents a unique case study of such an attempt, where modern tools and strategies for malaria treatment and vector control have been deployed since 2003.

“Zanzibar’s case is unique because they have been able to achieve consistent commitment by the national malaria elimination programme and participation by community residents,” says Dr Okumu. Globally, 40 countries and territories have been granted a malaria-free certification from WHO – including, most recently, China and El Salvador (2021), Algeria (2019), Argentina (2019), Paraguay (2018) and Uzbekistan (2018).

Despite the widespread use of insecticide-treated bed nets and indoor spraying, progress and the ability to maintain malaria prevalence below one percent for the past decade, experts note that the elimination of the deadly mosquito-borne disease remains elusive.

Whereas Zanzibar provides evidence of the feasibility of reaching significant and sustainable malaria reduction (pre-elimination) in a previously high endemic region, scientists say that new challenges call for novel tools and reoriented strategies to prevent a rebound effect and achieve elimination.

Zanzibar aims to eliminate malaria by 2023. But some of the new challenges include outdoor transmission, a large asymptomatic parasite reservoir, and imported infections.

“For Zanzibar, their focus is on preventing transmission while outdoors.