Lymphatic filariasis which can cause elephantiasis (or the enormous enlargement of limbs) continues to circulate around Samoa despite efforts to control the disease caused by infection by parasites.

The disease, which was the subject of a nationwide medical intervention in 2018, can “lead to the abnormal enlargement of body parts, causing pain, severe disability and social stigma”, according to the World Health Organisation.

The researchers were ultimately left without a conclusive explanation for the persistence of the disease. 

Researchers from the Ministry of Health and universities across Australia surveying nearly 4000 people across Samoa found 18 people with Microfilaria (Mf) in their blood, 14 of whom said they took a triple drug regimen designed to cure them.

Microfilaria is an early stage parasite. 

The survey identified 28 children between five and nine years old who had L.F. antigens in their blood and one with Mf, and well as 94 people over 10 years old with antigens. The participants were from 30 randomly selected villages and five intentionally selected villages based on previous research (Fasitoo-tai, Faleasiu, Laulii, Salua on Manono and Salelologa).

Lymphatic filariasis (L.F.) is a neglected tropical disease caused by an infection of worms carried by mosquitoes, and long term infection causes permanent swelling to the limbs called elephantiasis. It is known as mumu tutupa in Samoan and is endemic to Samoa. 

In 2018, Samoa was the first country in the world to deliver a triple drug therapy programme en masse to the population in a bid to stamp out the disease, which does not always display symptoms. The dosage of three separate drugs was calculated according to the patient’s body weight.

For those who do see symptoms, they suffer painful and disfiguring burdens that can spill over into mental health problems and socio-economic issues too.

To test whether there is ongoing L.F. transmission the World Health Organisation recommends surveys that look at threshold numbers of Antigen positive children. As well as gathering base data, the researchers wanted to test whether the Antigen survey is sensitive enough for identifying hot spots of L.F. transmission which have been previously identified in Samoa.

In 2011, researchers found hotspots in Fasitoo-tai, Falefa, and Siufaga. 

A survey of 3852 participants whose blood samples were tested for L.F. in the months immediately following the 2018 mass therapy programme (in order to gather baseline data for the 2018 programme) found despite decades worth of effort to eradicate the disease it remains in the community. 

“Given that the 2018 baseline survey was conducted 7-11 weeks after the first round of triple-drug M.D.A. (mass drug administration), it is surprising that our study identified 18 Mf-positive persons, 14 (78 per cent) of whom reported taking the M.D.A,” the researchers wrote.

They suggest several reasons for this high rate, including miscalculated dosage of the M.D.A. for body weight and even misreporting by the survey participant or survey staff.

Investigations suggest drug resistance is not likely and the participants who reported taking the dosage but came up Mf-positive anyway are being followed up closely.

“The reasons for L.F. resurgence in Samoa are unclear,” the researchers said.

From the tropical climate and amount of time people spend outdoors, “highly efficient” mosquitoes and infrequent older M.D.A. programmes all could have contributed to the resurgence, as well as potentially low coverage, low or non-compliance of the 2018 programme.

“Samoa was proactive and expedient in addressing the resurgence of L.F., with the first round of I.D.A. (the triple drug therapy) distributed in 2018, and the second round planned for 2020/2021 (delayed by measles outbreak and COVID-19).

“Follow-up surveys will assess the impact of two rounds of triple-drug M.D.A. on transmission. Other surveillance strategies being investigated in Samoa include spatial sampling strategies and molecular xenomonitoring (testing mosquito D.N.A.)”.

In total, the survey found antigen prevalence was lower in the younger children than in those older than 10, and that older people had antigen prevalence three times higher than children. 

“Sampling older age groups would provide more accurate estimates of overall prevalence, and be more sensitive for identifying residual hotspots,” the researchers suggest.