Overview 

Melioidosis is an infectious disease caused by a bacterium named Burkholderia pseudomallei, which is transmitted through the environment and can spread to several bodily organs. Contact of mucous membranes and/or open wounds with contaminated water, soil and even air can enable the entrance of the bacteria. Its occurrence is most common in tropical regions, especially during humid seasons in Southeast Asia and northern Australia. Once infected, the individual may present an acute case, which often leads to sepsis, a life-threatening condition where the immune system response is exacerbated. Infection may also be chronic, presenting symptoms for more than 2 months, or latent, which is when the bacteria exist in the body, but do not present symptoms. The risk of death from melioidosis varies from 10- 50%, depending on the type of manifestation. As it can affect a variety of organs, it has a wide range of symptoms and it is known to mimic other infections, making primary diagnosis difficult. Early detection is important to improve survival, as the active infection can evolve in a fast and dangerous manner.¹

Acute melioidosis

Manifesting symptoms after recent exposure to B. pseudomallei characterize an acute infection, which means that it develops rapidly and may prove fatal. For these cases, the interval between contact with a potentially contaminated environment and first signs is on average 9 days. It represents 85% of melioidosis cases and usually has severe consequences. The most common complication that arises from acute melioidosis is septicemia, or sepsis, in which the immune system orchestrates a systemic response. During sepsis, the body is intensely fighting a threat (in this case, the bacteria) but ends up damaging itself. It is a cascade of reactions that can rapidly cause dysfunction of multiple organs and even advance to death.¹ 

Besides sepsis, other severe presentations of acute melioidosis are pneumonia and abscesses (either in skin or on the surface of affected organs). It is hardly distinguishable from other acute infections, such as leptospirosis and malaria. As melioidosis does not present unique features and evolves fast, it is difficult to diagnose. Seasonal occurrence and possible exposure are an essential part in suspecting melioidosis.²

Common first symptoms 

• Fever 
• Cough 
• Chest Pain
• Muscle or Joint Pain
• Abdominal Pain 

Diabetes and risk of melioidosis

A high percentage of patients with a diagnosis of melioidosis also have diabetes mellitus (more than 50% worldwide), showing a strong correlation between both conditions. The reason is not completely clear, but it relates to the effect of diabetes on the immune system. Specific impairments by defense cells and suitable support recruitment in inflammation sites are a few of the disturbances that may contribute to infection severity. People with diabetes are considered a high-risk population for melioidosis.¹

Other risk factors for severe symptoms 

• Chronic Kidney Disease 
• Excessive Alcohol Consumption 
• Chronic Lung Disease

Subacute and chronic melioidosis

It is possible to be in contact with the causative agent of melioidosis and take longer than a few days to manifest symptoms; these cases can be either subacute or chronic infections. The time it takes for signs of subacute melioidosis to show varies,  but typically it can take from 2 to 4 weeks. It is an intermediate form, between acute and chronic, usually with similar presentations, but milder symptoms than acute melioidosis.³

Chronic melioidosis manifests after a longer period and lasts more than 2 months after exposure to contaminated water or soil. It is associated with an adaptation from the immune system to the infection, mainly characterized by abscess formation. Easily misinterpreted as tuberculosis, chronic melioidosis is known to mimic the disease in all its features and how the abscesses present. However, compared to acute melioidosis, death rates are much lower.^1,3,4

For both subacute and chronic forms, when the individual’s immune system is weaker, allowing for the bacteria to proliferate, it can progress into an acute infection.³

Symptoms and signs 

• Persistent Fever 
• Weight Loss 
• Night Sweats 
• Chronic Cough
• Abscess Formation (e.g., liver, spleen, prostate) 

Latent melioidosis

Infection by Burkholderia pseudomallei may not manifest symptoms, as bacteria remain dormant and non-proliferant in latent melioidosis.  Most of the time, individuals are unaware of their condition,  and this can last months or even years. The risk for latent melioidosis is the activation of the infection, causing acute symptoms with no apparent reason.¹ 

Triggers for reactivation 

• Immunosuppression: other diseases, chronic conditions, medication, and tumors
• Trauma 
• Stress

Melioidosis: A variety of symptoms

Melioidosis can present itself through a wide range of symptoms depending on the individual's susceptibility, bacterial load and the type of contact with contaminants. If un-lesioned skin is directly exposed to bacteria, the reaction may remain localized and superficial.  Nonetheless, bacteria can access other tissues through different routes. Infections can be carried through the system if there are skin lesions at the moment of contact, contaminated water is ingested, or air carrying contaminated water particles is inhaled. The pathway through which bacteria enter the body represents a variety of organs that become highly exposed to the menace. The majority of the documented symptoms are on the skin and lungs,  most likely due to the more common types of exposure. Regardless, any contact is potentially harmful and can result in infection, not to mention, it is impossible to predict how exactly it will affect the body.⁵

Possible manifestations

• Skin: ulcers, rashes, nodules
• Lungs: bronchitis, pneumonia, pressure imbalance
• Liver and spleen: abscesses, enlargement
• Overall: high fever, seizure, muscular pain

Diagnostic challenges

Each melioidosis case can be different, depending on the tissue affected and the damage caused by bacterial proliferation. Its wide range of signs and symptoms is not specific and can lead to other suspicions first, giving it the reputation of mimicking other diseases. For there to be a melioidosis diagnosis, investigations should go further than clinical and radiological exams.⁶

The most effective and definitive exam to identify B. pseudomallei infection is the microbiological analysis. No sign of such bacteria in human samples (blood, urine, material from abscesses) is viewed as normal and should always consider the possibility of melioidosis. Any other exam can attest to the patient's overall state, for example, imaging to detect organ damage, but will require further confirmation. Meanwhile, treatment targeting B. pseudomallei must start under any suspicion, since melioidosis is potentially fatal.¹

Differential diagnosis 

When affecting the lungs, melioidosis is commonly suspected to be tuberculosis. Both can manifest pulmonary abscesses and are non-responsive to conventional antibiotics. Clinical observations, like patients with diabetes and/or using corticosteroids, also present a risk for either one of the diseases.⁷ When differentiating melioidosis and tuberculosis, it is essential to identify the causative microorganism, which calls for a microbiological analysis. In regions prone to melioidosis cases, some clinical details can’t be missed. Septic arthritis (infection of the joints), osteomyelitis (an infection of the bone) and involvement of other organs besides the lungs can raise suspicion of melioidosis rather than tuberculosis.⁸ 

Summary

Melioidosis is a disease caused by the bacteria Burkholderia pseudomallei. Infection can arise through contact with contaminated water or soil. It is endemic to tropical regions like Southeast Asia and northern Australia. Melioidosis damage and symptoms are related to the type of exposure to contaminants, bacterial load and if the individual’s profile is at a higher risk of infection (diabetes, immunosuppression). A variety of tissues can be affected, but the most common are the skin, lungs, spleen and liver. For that reason, it presents non-specific symptoms, like high fever, muscular pain, seizures, abscesses, which gives melioidosis the reputation of mimicking other diseases. This can result in it being misdiagnosed as tuberculosis, leptospirosis, malaria and even cancer. Acute, chronic and latent are the three forms in which an individual can carry the infection. In acute melioidosis, bacteria rapidly proliferate and reach the bloodstream, which can trigger severe symptoms, commonly leading to septicemia, a life-threatening condition. Chronic melioidosis can last years, but with milder symptoms. In latent melioidosis, the bacteria are dormant and the individual presents no symptoms, but when the immune system is vulnerable, infection can progress into an acute state. Raising awareness for melioidosis is important for both the overall population and healthcare professionals. Being alert to seasonal occurrences, regions affected, and possible exposure can support early diagnosis, which can be life-saving.