Research into a pathogen which can cause serious illness in foals has produced a promising lead for a vaccine.
It is hoped the research to understand the genetic structure of Rhodococcus equi may lead to new measures to control the disease in foals.
Professor Jose A Vazquez-Boland, from the Microbial Pathogenesis Unit at Edinburgh University, told the recent Thoroughbred Racing and Breeding Seminar in Britain of progress made in understanding the biology, ecology and virulence mechansisms of Rhodococcus equi through studying its genetic structure.
It typically affects foals up to six months old, causing chronic broncho-pneumonia with abscesses in the lungs. Other forms of the disease can occur, including infection of the intestine and lymph nodes.
Rhodococcus equi does not only infect horses. It is an opportunistic human pathogen associated with immune suppression diseases. Up to 4 percent of suspected bovine tuberculosis cases at the abattoir are, in fact, due to the organism.
It is found in soil, especially where horse dung is present, which provides the substrate on which it feeds. It is well equipped to resist drying out. Foals are infected by inhaling dust contaminated with Rhodococcus equi.
Treatment is difficult. The organism is resistant to many common antibiotics. It lives within the macrophages, making it difficult for antibiotics to reach it.
A long course of suitable antibiotics, such as erythromycin and rifampin, is required to effect a cure.
Understanding the complex mechanisms used by the bacteria to cause disease may reveal the microbe's weakness that could be targeted by vaccines and drugs.
Researchers have identified several features that indicate that it is well-suited to its environment. It has a unique metabolism, different from most bacteria, as it feeds not on sugars but on short chain fatty acids, such as lactic acid and acetic acid (found in the intestine.) It therefore doesn't compete with the bacteria in the horse's gut, but feeds off their by products.
It has genes that confer resistance to many antibiotics.
"Among the virulence factors we have identified, we have found one in particular that we think might be a good target for a vaccine," he said.
Disease-causing strains of the bacteria have long processes, or "pili", which they use to attach to the host cells.
"We identified the genes responsible ('Rp1 adhesin') and raised antibodies against them."
These antiRp1 antibodies prevent the bacteria attaching to the cells and so prevent infection getting established. It would therefore be a good candidate for a vaccine.
The foal's immune system is not well developed at the time it is exposed to infection, meaning there is little chance of producing a vaccine that can be used in the foal.
However, by vaccinating the mare, it may be possible to protect the foal with passive immunity through the colostrum.
Facebook page
Twitter
HOME SITES 
