Smartphone app used to scan blood for parasites

Behind the Headlines

Thursday May 7 2015

Loa loa parasites are found in west and central Africa

Parasites in your blood? There's an app for that

"A smartphone has been used to automatically detect wriggling parasites in blood samples," BBC News reports. It is hoped the customised device could help in programmes to get rid of parasites in parts of Africa.

In certain regions of Africa, two parasitic diseases – river blindness and elephantiasis – are a major health problem affecting millions. Both of these diseases can be treated with a drug called ivermectin.

But if you give somebody ivermectin and they also have high numbers of a less harmful parasite called Loa loa (African eye worm) inside their body, it can trigger potentially deadly side effects.

This has hampered large-scale ivermectin treatment programmes aimed at eradicating river blindness and elephantiasis in some areas,  as people need to have time-consuming tests for Loa loa levels before they can be treated.

The new device – a standard iPhone hooked up to a specially designed lens module – allows people with minimal training to quickly measure Loa loa levels in a sample of blood.

This study found the device performed similarly to standard, more time-consuming, laboratory tests performed by trained technicians.

But this was a small pilot study in just 33 people, and larger studies are needed to confirm the technique's accuracy.

The development of a technique that could be carried out quickly in the field without much specialised equipment could be an important step forward in treating these parasitic diseases.

The researchers speculate the device could also be used to detect other moving disease-causing parasites in the blood. 

Where did the story come from?

The study was carried out by researchers from the University of California, the National Institute of Allergy and Infectious Diseases in the US, the Centre for Research on Filariasis and other Tropical Diseases, and the University of Yaoundé, Cameroon and the University of Montpellier, France.

It was funded by the Bill and Melinda Gates Foundation, the University of California, the US Agency for International Development, the Purnendu Chatterjee Chair Fund, and the National Institute of Allergy and Infectious Diseases.

Some of the researchers hold patents or have applied for patents relating to this new approach, and two hold shares in the company that developed the device.

The study was published in the peer-reviewed journal, Science Translational Medicine.

The BBC's coverage was fair and included a comment from an independent expert in the UK. 

What kind of research was this?

This laboratory study looked at whether a mobile phone video microscope could accurately detect and measure the amount of a parasitic worm called Loa loa (African eye worm) in a drop of a patient's blood.

In certain regions of Africa, parasitic diseases are a major public health problem affecting millions of people. In particular, an infection called onchocerciasis, or river blindness, is the second most common cause of infectious blindness worldwide, and can also result in disfiguring skin disease.

Lymphatic filariasis leads to elephantiasis, which is marked by disfiguring swelling and is the second leading cause of disability worldwide.

Both these diseases can be treated with the antiparasitic drug ivermectin, but this can have dangerous side effects for patients who are also infected with Loa loa.

When there are high numbers of microscopic Loa loa worms in a patient's blood, treatment with ivermectin can lead to severe and sometimes fatal brain damage. The authors say this has led to suspension of mass public health campaigns to administer ivermectin in central Africa.

At present, the standard method of assessing Loa loa levels involves trained technicians manually counting the worms using conventional laboratory microscopes. This process is impractical for health professionals working in communities where they do not have access to labs, or in large ivermectin treatment campaigns.

This study tested a new method researchers developed for detecting Loa loa, which uses a smartphone camera and avoids the need to send samples to a lab. 

What did the research involve?

To test the accuracy of the new technique, researchers compared it with gold standard microscope analysis in a laboratory. They did this for blood samples taken from 33 people in Cameroon, who were all over the age of six and were potentially infected with Loa loa.

The new technique uses a mobile phone-based video microscope that automatically detects the tell-tale wriggling movement of the worms. It examines a fingerpick sample of blood using time lapse photography and uses this characteristic movement to count the worms.

The process uses an iPhone 5 camera attached to a 3D-printed plastic base, where the sample of blood is positioned. Control of the device is automated through an app the researchers developed for the purpose.

The patients' blood was taken from a finger prick and then loaded into two rectangular capillaries to obtain duplicate measurements. A series of videos was taken of each sample by the mobile phone software.

The researchers say it takes a minute to prick the finger and load the blood on to the capillary, and the whole process takes two minutes maximum, starting from the time the sample is inserted to the phone displaying results.

In total, 5 or 10 videos were taken of each sample, resulting in some 300 videos. Sixteen of these were excluded from the analysis either because of inconsistent counts or device malfunction.

Blood was also taken from each patient for gold standard laboratory analysis for Loa loa worms. These samples were transported to a central laboratory for assessment by two independent technicians.

The counts from this analysis were used to assess whether the Loa loa worm count was below the level at which it was safe to treat patients with ivermectin. This was called the treatment threshold.

The researchers then compared results from the smartphone microscope with those from the laboratory.   

What were the basic results?

The researchers found the Loa loa worm count measured by the mobile phone video was very similar to the results from the laboratory. Compared with the laboratory analysis, among the smartphone samples:

  • there were no false negatives – that is, there were no patients who had a worm count above the safe treatment threshold of gold standard methods who were incorrectly identified as safe for treatment by the smartphone technique
  • there were two false positives – that is, two patients whose worm count fell below the safe treatment threshold by gold standard methods were incorrectly identified as not safe for treatment by the smartphone technique

This meant the mobile phone device had:

  • 100% sensitivity – this measures how good the test is at identifying those with an unsafe worm count and who should not be treated with ivermectin
  • 94% specificity – this measures how good the test is at identifying those with a safe worm count who could be treated with ivermectin; this means 6% of people tested would be told their worm levels were unsafe when in fact they were safe  

How did the researchers interpret the results?

The researchers say this new technology could be used at the point of care to identify patients who could not be treated safely using ivermectin.

They say this would allow the mass drug treatment for both river blindness and elephantiasis in central Africa to be resumed.   

Conclusion

This study suggests a new smartphone-based approach could provide a quick way of measuring levels of infection with the Loa loa worm in blood samples, and with a high level of accuracy.

This technique could allow assessment of people's infection in communities without easy access to the laboratory testing that is usually used to detect the worms.

This is important, as people with high levels of this infection can suffer potentially fatal side effects with the drug ivermectin, which is used to treat two other parasitic infections.

It's worth bearing in mind that this was a pilot study in only 33 people using a prototype device. The new device will require more refinement and testing to make sure it performs well enough before it can be put into practice. 

The test seemed to correctly pick up all people with worm levels that would make ivermectin unsafe, but did class 6% of people as having unsafe levels when in fact laboratory tests found they had safe levels. This means that 6% of people might miss out on ivermectin unnecessarily.

If its accuracy is confirmed, this new approach could allow health workers to quickly determine on site whether it is safe to give someone ivermectin for the treatment of river blindness or elephantiasis.

Elephantiasis is a leading cause of preventable disability in the developing world, while river blindness is the second leading cause of infection-related blindness. Approaches that allow cheap, effective and safe mass treatment programmes could have an important impact on health.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Smartphone 'scans' blood for parasites. BBC News, May 7 2015

Links to the science

D'Ambrosio MV, Bakalar M, Bennuru S, et al. Point-of-care quantification of blood-borne filarial parasites with a mobile phone microscope. Science Translational Medicine. Published online May 6 2015

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