glanders

International Common Names

• English: farcy

Glanders is a highly infectious zoonotic disease of equids (horses, donkeys, mules), caused by the bacterium Burkholderia mallei (Cárdenas et al., 2019). It is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). Glanders is characterized by chronic suppurative lesions of skin and mucous membrane, pneumonia, and septicaemia. The disease has been eradicated in most European and North American countries, but outbreaks still occur in South America, parts of Africa, the Middle East and Southern Asia (OIE, 2020). The acute form of glanders is usually observed in donkeys and mules with high fever, respiratory symptoms, and death occurring within a few days. The disease is mainly chronic in horses and latently-infected animals pose a high risk of reintroduction of the infection into glanders-free countries (Khan et al., 2013). Quarantine testing before and after the international transport of horses is very important to prevent the spread of glanders (Kinoshita et al., 2019). As a highly infectious agent that can be transmitted by aerosol, causing fatal disease in humans, B. mallei is considered to be a biothreat agent (Scholz et al., 2014).

In equids, findings include nodules, granulomas and/or ulcers in various tissues. The upper respiratory tract is often affected, with ulcers, nodules and/or stellate scars in the nasal passages, larynx and other tissues. Internally, nodules are most likely to be found in the lungs. Nodules and other lesions may be detected in other visceral organs, particularly the liver and spleen. Swollen lymphatics, with chains of nodules and ulcerated nodules, may be found in the skin, while the lymph nodes may be enlarged, congested and/or fibrotic, and can contain abscesses (Spickler, 2018).

The incubation period in equids is reported to range from a few days to many months, but many cases become apparent in 2-6 weeks (Spickler, 2018). There are three clinical forms of the disease in equids: nasal, pulmonary and cutaneous (farcy) glanders. Clinical cases are often a combination of the three forms, and may be acute (or subacute), chronic or latent. Nasal and pulmonary forms tend to be more acute in nature, while the cutaneous form of the disease is a chronic process (OIE, 2020).

Acute cases are typically fatal in a few days. Animals show signs of respiratory disease, cough and fever and the release of an infectious nasal discharge, followed by septicaemia and death within days. In the chronic form, nasal and subcutaneous nodules develop, eventually ulcerating (Marsella, 2019). A latent form of glanders has also been described but may provoke few signs, e.g. nasal discharge and dyspnoea. Donkeys and mules often develop acute glanders after exposure, although mules appear to be somewhat more resistant and the course of the illness may be slower. Horses usually develop chronic glanders (OIE, 2020).

The transmission of B. mallei occurs by direct contact (Cárdenas et al., 2019). Glanders can spread widely when large numbers of animals are in close contact. A common source of infection appears to be ingestion of food or water contaminated via discharges from the respiratory tract or ulcerated skin lesions from carrier animals. Subclinical carriers are often more important in transmission of disease than clinical cases: Chronically or subclinically infected equids can shed B. mallei intermittently or constantly into food and water troughs. There are reports of venereal transmission from stallions to mares, and vertical transmission from the mare. B. mallei is readily spread with fomites (OIE, 2020). This disease is reported to be more common in animals that are undernourished or otherwise in poor condition (Spickler, 2018).

Throughout the western world, glanders has been eradicated through large scale culling of infected animals. In developing countries, however, economic and cultural circumstances may hinder culling of asymptomatic animals and enable the persistence of glanders (Scholz et al., 2014). The disease is considered endemic in many developing countries of Asia, Africa and South America (Ghori et al., 2018).

In Brazil, glanders remains a serious problem, with the obligatory sacrifice of disease-positive animals without compensation. Each year, glanders cases are reported in several regions of the country, causing severe economic losses and trade restrictions (Fonseca-Rodríguez et al., 2019).

Due to weaknesses in the diagnosis of glanders, coupled with the increased movement of horses, infection with B. mallei remains a major risk in the context of international movement of equids (Kettle and Wernery, 2016).

Humans may acquire the infection through direct contact with the organism and prolonged contact with diseased animals. Veterinarians, horse caretakers and laboratory workers handling this organism are considered as the professional risk groups. The most common manifestations are life-threatening pneumonia and bacteraemia. Although, early and aggressive treatment with combinations of systemic antibiotics can be curative (Srinivasan et al., 2001), an extremely high rate of mortality can occur in untreated humans (Praveen Malik et al., 2015). There is no vaccine to protect against B. mallei and there is concern regarding its potential use as a biothreat agent (Jelesijevic et al., 2015).

Antibiotic treatments have been used in endemic zones, but this may lead to subclinical carrier animals that can infect humans and other animals (OIE, 2020). It is believed that partially treated equines with chronic or subclinical infection may be responsible for frequent and continuous outbreaks of glanders in India (Praveen Malik et al., 2015).

Designing effective treatments for glanders is complicated by differences in antibiotic susceptibility patterns between B. mallei isolates, and the inability of some drugs to penetrate into the host cells where this organism replicates (Spickler, 2018).

Muhammad Saqib et al. (2012) note that certain situations e.g. wild life conservation, highly valuable breeding stock, could benefit from effective treatment schemes and post-exposure prophylaxis. They describe a treatment protocol of 12 weeks duration based on the parenteral administration of enrofloxacin and trimethoprim + sulfadiazine, followed by the oral administration of doxycycline during a confined glanders outbreak in horses in Lahore, Pakistan. Although the treatment was successful, they conclude that more studies are needed to test the effectiveness of this treatment regime on B. mallei strains from different endemic regions. Furthermore, due to its cost and duration, this treatment can only be an option in certain situations and should not replace the current “testing and culling” policy, in conjunction with adequate compensation to prevent spreading of disease.