Small RNA-Seq test could transform care for costly cattle disease

Efforts to develop a field-side test for animal trypanosomiasis could transform management of the common, costly infection in smallholder farms.

Across parts of sub-Saharan Africa, the range of the native tsetse fly overlaps with a significant number of cattle farming regions.

In the affected countries – 40 in all – tsetse flies spread infection from trypanosome parasites to cattle through their bites.

This leads to about 3 million cattle deaths every year from Animal African Trypanosomiasis (AAT), or the cattle equivalent of sleeping sickness. Millions more animals fall sick or are at risk of infection.

The condition, caused by three trypanosome parasites, is considered the greatest infectious disease livestock production problem in sub-Saharan Africa, with an economic impact of US$4.5 billion.

Better management of AAT would support food security and efforts to alleviate poverty in affected regions.

Lack of treatment 

No vaccine is available for AAT, and drugs to treat infection, although inexpensive, have not been updated in decades. Consequently, drug resistance is on the increase.

Diagnosis of the disease can help to minimise its impact in a smallholder setting, but this is often based on clinical signs, typically anaemia, which are not specific to trypanosome infections.

More sophisticated tests to indicate disease, such as microscopy analysis, are limited in their practicality.

Diagnostic quest 

Researchers at the Roslin Institute are endeavouring to develop a diagnostic test that is affordable, sensitive, and specific, and can be used in a smallholder setting.

Their developing technology is based on small RNA – short strands of genetic material whose roles relate to the function and maintenance of genes.

The team investigated whether a small RNA molecule might be produced by parasites in infected cattle, and if this could be used as the basis for a diagnostic test.

Biological marker 

Using small RNA sequencing technology to analyse samples of the Trypanosoma congolense parasite species cultured in the lab and recovered from infected cattle, the team was able to identify an RNA molecule produced at high levels in affected cattle.

They worked with partners Life Technologies to develop a PCR test to detect the RNA molecule – known as 7SL – in real time. The test, involving a two-stage process, is highly sensitive and species-specific.

With support from Wellcome, they tested and developed their technology.

A three-month study of plasma from live cattle showed that the RNA test could indicate positive results very soon after infection before clinical signs emerged.

Sensitive and specific 

The test was sensitive enough to detect the RNA signal when levels of parasites were relatively low and was able to predict relapse following a temporary drop in parasite load.

Drug treatment for infection with T. congolense in affected cattle eliminated the RNA biomarker signal, indicating recovery from infection.

The team’s technology was able to perform as well as the best comparable diagnostic, with rapid signal decay following effective drug treatment.

They continue to develop their sensitive, specific test with the goal of developing a lateral flow field diagnostic and hope to further develop sensitive, specific non-PCR test for markets in Africa and beyond.

“There is an urgent need for in-field technology that can enable farmers to diagnose infection and respond rapidly to minimise its impact. A specific, sensitive, affordable lateral flow, such as that which we have developed, could provide valuable details on the health of cattle at the early stages of trypanosome infection and beyond.”

Professor Liam Morrison – Roslin Institute

SourceThe Roslin Institute, University of Edinburgh

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