Glanders, or malleus, is a serious disease affecting horses and other equines, such as donkeys and mules. Other animal species are also susceptible, including camels.
Other animal species are also susceptible, including camels. Infected animals may die within a few weeks, but the disease can also become chronic, with the result that it can be transmitted for years. Humans may also become infected, although this occurs only rarely. Without timely treatment with antibiotics, the disease can be life-threatening.
Disease subject to mandatory eradication
Glanders is an infectious animal disease that is subject to mandatory eradication, in the same way as foot-and-mouth and swine fever. In the Netherlands, preventing and eradicating glanders is a task carried out by the state. Wageningen Bioveterinary Research has core responsibilities here in fields of diagnosis, advice and training. We also conduct testing for the export of animals.
Glanders should, however, not be confused with strangles. The latter is caused by the bacterium Streptococcus equi and occurs – by contrast with glanders – frequently in horses in our country.
Glanders is caused by the bacterium Burkholderia mallei, known previously as Pseudomonas mallei. It is closely related to the bacterium that causes Meliodisos, Burkholderia pseudomallei.
Burkholderia mallei is inactivated by virtually all standard disinfectants. The bacterium is killed by heating (10 minutes at 55 °C) and is sensitive to UV radiation.
Until the middle of the last century, glanders frequently occured 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.
The disease was successfully eradicated in many countries, and today it occurs only rarely in Europe and North America. Glanders no longer occurs in the Netherlands.
Germany is also glanders-free. But an infection with Burkholderia mallei was found in Germany in January 2015 in a horse being tested for export. The Complement Fixation Test (CFT) was positive, as well as the following confirmation by the German national reference laboratory, the Friedrich Löffler Institute (FLI, also the OIE reference laboratory for glanders). Although the horse concerned showed no clinical symptoms of glanders and there were no epidemiological indications for this infection, the animal was confiscated and an autopsy carried out. No B. mallei could be shown bacteriologically, although a PCR test on skin samples was positive. It is not known how the animal contracted the infection. The horse was born in 2008 and had not been outside Germany. There may possibly have been indirect contact with South America. All the other horses on the farm tested negative.
Glanders does still occur 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. See WAHID Technical Disease Cards, keyword glanders.
Glanders takes several different forms in animals. The disease may be subdivided on the basis of the location of infection (nasal, pulmonal and cutaneous forms), 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, possibly leading 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 in this case as well, possibly accompanied 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 belly 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.
Glanders is transmitted primarily via infectious liquids (exudate) (nasal discharge, pus) from infected animals, without these symptoms even having to reveal themselves. The bacteria 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.
The bacteria are rendered harmless by heat and sunlight, but can survive for a lengthy period (weeks up to months) under moist conditions.
Humans are infected through contact with diseased animals or via contaminated materials. The infection generally occurs as a result of the fact that bacteria can penetrate 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).
Laboratory tests are essential in order to confirm or rule out glanders definitively. The bacteria can be shown 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 risk that a horse or other equine 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. There is an international agreement that this is done by means of a Complement Fixation Test (CFT test) in serum (OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals). This test is conducted by us routinely (within 3 working days).
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 occaision that a test yields a false positive. This has only happened on only a few occasions at Wageningen Bioveterinary Research over recent years. 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.
An exceptional case of a horse with a false positive result from a blood test for malleus occurred at the end of 2013. A horse originating in the Netherlands was tested negative before export, but on arrival in the US, a positive reaction was found in the animal in the test conducted there. On the basis of this test, the horse was not allowed to enter the US. On return to Schiphol, the animal was placed in quarantine, and a fresh blood sample was tested negative by Wageningen Bioveterinary Research. Material from the same serum sample was also sent to the glanders reference laboratory in Germany (the Friedrich Löffler Institute, FLI). Here too, no antibodies were shown.
Partly at the request of the exporters, Wageningen Bioveterinary Research mediated in the matter. A few weeks later blood was once again taken from the horse and sent to different laboratories by Wageningen Bioveterinary Research. Apart from Wageningen Bioveterinary Research itself, the serum was tested by the American reference laboratory (USDA) which had tested the horse positive previously. It was also sent to the European reference laboratory for infectious horse diseases in France (Anses) and to two international (OIE) reference laboratories for glanders, namely the abovementioned FLI in Germany and the Central Veterinary Research Laboratory (CVL) in Dubai. On the basis of all the collected test results, it was shown irrefutably that no glanders was present, and the horse was allowed into the US after all.