Summary

A medRxiv preprint reports that none of 7,388 people screened across 12 local government areas in Nigeria’s Osun State tested positive for circulating filarial antigen. The researchers say the result supports progression to the first transmission assessment survey, while chronic elephantiasis cases still showed substantial blood-count abnormalities.

A preprint evaluating lymphatic filariasis control in Nigeria’s Osun State reports 0% antigenemia among 7,388 people screened across 12 local government areas (LGAs). The researchers say the result is below the World Health Organization’s stated threshold of less than 2% and supports moving to a first transmission assessment survey, or TAS1.

The study, posted on medRxiv on 15 September 2026, combined a pre-transmission assessment survey and epidemiological monitoring survey with blood-profile analysis in people living with clinical elephantiasis. Lymphatic filariasis is a mosquito-borne parasitic disease that can damage the lymphatic system; long-term infection can lead to chronic swelling and elephantiasis.

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Survey results support the next elimination milestone

The researchers tested participants for circulating filarial antigen using Abbott Filarial Test Strips. They report that antigen prevalence at sentinel and spot-check sites had fallen below the relevant threshold, with no positive antigen results recorded across the surveyed LGAs.

Pre-TAS and epidemiological monitoring are used to check whether areas that have received mass administration of medicines, described in the paper as MDA/MAM, have reached the level required for a subsequent transmission assessment. TAS1 is the next assessment stage in the elimination pathway. The study authors interpret Osun State’s findings as evidence that it has entered a post-transmission phase, while also calling for continued monitoring to protect that progress.

The result concerns the people and locations included in this survey. It is an important programme milestone, but permanent elimination depends on maintaining sufficiently low transmission over time and completing the required follow-up assessments.

Participation in mass drug administration varied widely

Across the surveyed areas, the average reported individual participation in MDA/MAM programmes was 56.09%. Coverage varied substantially between LGAs. Ola-Oluwa recorded the highest participation at 84.70%, while Ilesha East recorded the lowest at 18.97%.

That difference gives public-health teams a practical indicator for targeting future programme work. The authors describe the overall participation level and the variation between LGAs as a potential vulnerability for sustained disease control, even though the antigen survey found no positives in the current assessment.

Chronic cases showed persistent blood-count changes

The second part of the study examined haematological profiles in patients with clinical elephantiasis. The researchers report a pattern they describe as immune suppression, including reductions in total white blood-cell and lymphocyte counts, persistent monocytosis and eosinopenia.

These measurements provide information about the physiological state of people living with chronic disease. They also show why reaching low transmission levels does not immediately remove the health burden among people who already have long-term lymphatic damage. The abstract does not state the number of elephantiasis patients assessed or provide comparator details, so the blood findings are best interpreted as a profile of the chronic cases included in this evaluation rather than a population-wide estimate.

The work is a medRxiv preprint, meaning it is being shared before formal peer-reviewed publication. It nevertheless supplies field-surveillance results from 12 LGAs, reports the test method and sample size, and links the findings to a specific programme decision: whether Osun State can proceed to TAS1.

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