Endemic in parts of Africa, epizootic lymphangitis (EZL) is a devastating and poorly understood fungal disease with severe health and welfare consequences in working equids. But newly developed tests could lead to faster, low-cost diagnosis and enable better management.
British and Ethiopian researchers teamed up to trial a molecular diagnostic test that would detect the presence of the fungus Histoplasma capsulatum var. farciminosum (HCF) in blood or pus that oozes from EZL wounds. This new DNA-based test provides more accurate results in much less time than do standard laboratory culture methods and could be adapted for surveillance in endemic regions. It should eventually become far less expensive as well, said Claire Scantlebury, BSc, BVSc, PhD, MRCVS, of the University of Liverpool’s School of Veterinary Science, in the U.K.
“At present, the findings presented in this paper show that it is possible to bypass the culture of equine Histoplasma (a notoriously difficult and time-consuming process that can take up to six weeks to gain diagnostic confirmation) and diagnose the infection directly from clinical samples of pus and, for the first time, equine blood, using nested polymerase chain reaction (PCR) methodology,” she said.
Scantlebury and her fellow researchers evaluated the test’s efficacy on 29 horses with clinical signs of EZL and 20 horses without. The blood test confirmed HCF infection in 25 of the sick horses (meaning the other four might not have had HCF circulating in their blood due to the stage of the disease or the presence of another disease with similar signs), and it even detected HCF in two horses that were not (yet) symptomatic, she said.
EZL can cause open, oozing skin wounds that gradually worsen and lead to lameness, as well as sores in the eyes and respiratory problems. If qualified veterinarians treat the horses with systemic iodides and a topical iodine tincture in the early stages, the horses can recover in about a month. But if the disease is advanced, euthanasia is the most welfare-appropriate option in this low-income working equid population, said Nigatu Aklilu, DVM, MSc, assistant professor of veterinary epidemiology and country director for the SPANA (the Society for the Protection of Animals Abroad) Ethiopia Project at Addis Ababa University, in Debre Zeit, Ethiopia.
[image imageid="4069" includeTitle="false" includeSummary="false"]If EZL has reached an advanced stage, euthanasia is the most welfare-appropriate option in this low-income working equid population.[/image]
Unfortunately, he added, many owners do not have their sick equids euthanized. If they become too weak to work or too unsightly because of their oozing and bad-smelling wounds, the owners sometimes abandon them.
“Once abandoned, the horses lack feed, water, and shelter and stand in the middle of highways,” Aklilu said. “This may further make them prone to traffic accidents. Moreover, they are most infectious at this time, with pus discharge and flies covering the lesions, and can spread the disease to others. It’s a debilitating disease with progression to death over a period of months. So it’s a huge problem that comprises equine welfare.”
To complicate matters further, scientists still know very little about EZL, including how it’s spread and how it can be prevented, Scantlebury said. But her group’s research could begin opening doors to better management.
“My co-authors and I are hopeful that the methods presented in our current research paper could contribute to improved diagnostics in the field,” she said. “The tools are now validated and available to conduct large-scale population-based studies to start to fill in some of these knowledge gaps and support the design of context-appropriate disease intervention strategies.”
The study, “Development and Evaluation of a Molecular Diagnostic Method for Rapid Detection of Histoplasma capsulatum var. farciminosum, the Causative Agent of Epizootic Lymphangitis, in Equine Clinical Samples,” was published in the Journal of Clinical Microbiology.