Glanders, or malleus, is a serious disease affecting horses and other equids, such as donkeys and mules. Other animal species are also susceptible, including camels.
The bacterium can affects horses and other equids, such as donkeys and mules. Other animal species are also susceptible, including camels. Infected animals may die within a few weeks, but glanders can also become chronic, with the result that it can be transmitted to other animals for years. There is no vaccine available against glanders.
Glanders is a zoonosis. Humans may also become infected, although this occurs only rarely. Without timely treatment with antibiotics, the disease can be life-threatening.
Glanders is an infectious animal disease that is subject to mandatory eradication. On behalf of the government in the Netherlands, Wageningen Bioveterinary Research has core responsibilities in the field of diagnosis, advice and training. WBVR also conducts the testing required for the export of animals.
Glanders is caused by the bacterium Burkholderia mallei, known previously as Pseudomonas mallei.It is closely related to the bacterium that causes melioidosis, Burkholderia pseudomallei.
Burkholderia malleiis inactivated by virtually all standard disinfectants. The bacterium is killed by heating (10 minutes at 55 °C) and is sensitive to UV radiation. The bacteria can survive for a lengthy period (weeks up to months) under moist conditions.
Glanders should not be confused with strangles. The latter is caused by the bacterium Streptococcus equi and occurs – by contrast with glanders – frequently in horses in the Netherlands.
Clinical signs glanders
Glanders can present in several forms in animals. The disease may be subdivided on the basis of the organ system affected by the infection (nasal, pulmonal and cutaneous form), or according to the course of the disease, namely acute (usually associated with donkeys) or chronic (often with horses in regions where it is endemic). In acute cases of glanders, the animals die within a couple of days to a few weeks. In addition, a latent form of glanders has also been described, where the symptoms remain limited to nasal discharge and difficulty in breathing.
This form begins with high fever, loss of appetite and difficulty in breathing, with coughing. Thick, yellow-green pus is discharged from the nose, which can lead to crusts around the nostrils. Small bumps or boils may be seen on the nasal mucous membrane. A purulent discharge from the eyes may also occur. The local lymph nodes are enlarged and inflamed, and may ultimately break through. The pus is extremely infectious.
In general, this form takes a number of months to develop. The initial symptom is fever, which is followed later by shortness of breath, (constant, dry) cough and breathing difficulties. All of this leads to increasing loss of stamina.
Here as well, the symptoms of the disease may only be seen a long time after the start of the infection. Fever may occur in the initial stage and the lymph glands may be enlarged. As the disease runs its course, small bumps (sources of infection) occur in the subcutaneous tissue along the course of the lymphatic vessels of the legs, breast and abdomen area. When these break through, a yellow, purulent exudate is discharged. Infected lymphatic vessels may become visible as thickened, cord-like lesions on the legs. This form is often accompanied by coughing, shortness of breath and general weakness..
Photo's of clinical signs, with thanks to Central Veterinary Research Laboratory, Dubai, UAE
Spread of glanders
Until the middle of the last century, glanders frequently occurred in horses across the world. It was even used as a biological weapon during the First and Second World Wars, when horses were still important to the military.
Glanders still occurs in certain regions, including parts of the Middle East, Asia, Africa and South America. Cases of glanders are regularly reported in Brazil, China, India, Iran, Iraq, Mongolia, Pakistan, Turkey and the United Arab Emirates.
The disease was successfully eradicated in many countries, and today it occurs only rarely in Europe and North America. The Netherlands are considered free of glanders.
Glanders is transmitted primarily via infectious body fluids (exudate, nasal discharge and pus) from infected animals, possibly without any visible symptoms. The bacterium can also easily be transmitted via contaminated feed or water, or by contact with contaminated objects, such as saddles, riding tack or grooming materials, such as brushes.
Humans are infected through contact with diseased animals or via contaminated materials. The infection generally occurs as a result of the bacteria penetrating the skin via small cuts or abrasions, but may also occur as a result of eating or drinking contaminated food or water, or by inhaling contaminated aerosols (small solid or fluid particles floating in the air).
Prevention and control of glanders
No vaccine against glanders is available. Horses are tested for the presence of antibodies to Burkholderia mallei, before they are transported to other countries, in order to prevent introduction of the disease.
While serologic testing of this kind is highly reliable, it may happen on occasion that a test yields a false-positive result. In cases of this kind, the blood test is repeated, and a blood sample is also sent to (another) reference laboratory. To date, it has been possible to rule out infection with glanders on the basis of these results.
Laboratory tests are essential in order to confirm or rule out glanders. The bacteria can be detected by means of culture, but it is important that this happens in a laboratory set up for working with extremely infectious pathogens of this kind that are also dangerous to humans. These laboratories are called Biosecurity Level 3 (BSL3) laboratories. Wageningen Bioveterinary Research is the only veterinary laboratory in the Netherlands that has this certification.
The chance that a horse or other equid is found with this disease in the Netherlands is small. However, diagnosis is routinely conducted for export purposes. Many countries require a blood test for the presence of antibodies to the pathogen that causes glanders before horses may be imported into the country concerned. The complement fixation test (CFT) is recommended by the OIE for this purpose.