Outbreak of “Disease X” in Congo

A mysterious illness, dubbed "Disease X," has emerged in the Democratic Republic of the Congo (DRC), causing concern among health officials and the public. As of December 2024, this disease has infected over 400 people and resulted in a significant number of deaths (more than 100), with more than half of the deaths occurring in children younger than 5 years old who were severely malnourished (Figure 1). Women and children appear to be the most severely affected demographics. Symptoms include flu-like conditions such as fever, headache, cough, and anemia. The region faces challenges such as food insecurity, low vaccination coverage, and limited access to healthcare, which may exacerbate the outbreak's impact. The cause of the outbreak remains unidentified.

Disease X is a placeholder term adopted by the World Health Organization (WHO) to represent a hypothetical, as-yet-unknown pathogen that could cause a future epidemic or pandemic. It highlights the need for global preparedness against emerging infectious diseases that might arise suddenly, spread rapidly, and have significant public health consequences. The term gained real-world resonance after the COVID-19 pandemic caused by the SARS-CoV-2 virus, which could be considered an example of a "Disease X."

In Congo, the most recent Disease X presents a range of symptoms similar to other respiratory infections. Common symptoms include:

• Fever
• Cough
• Fatigue
• Runny nose
• Headache

In severe cases, individuals may experience difficulty breathing, anemia, and signs of acute malnutrition. Most of these symptoms are consistent with known infectious diseases such as Covid, a common cold, or flu. Anemia is a symptom of malaria. 

The transmission mechanism of Disease X is still unclear because the pathogen (if any) remains unknown. While the Africa Centers for Disease Control and Prevention has suggested that the disease may be airborne, further investigation is needed to confirm this. It is likely that both malaria and malnutrition are exacerbating the symptoms. 

Health officials are actively investigating potential causes, including:

• Acute pneumonia
• Influenza
• COVID-19
• Measles
• Malaria

Initial laboratory analyses suggest that malaria may be a contributing factor, as 10 out of 12 initial samples tested positive for the mosquito-transmitted infection. However, authorities believe that more than one infection may be involved in the outbreak. While named "Disease X," it is important to remember that most outbreaks are caused by known pathogens, so this outbreak is likely not caused by a completely new pathogen.

Health officials in Congo (DRC) have faced numerous challenges trying to identify the cause of the disease. For one, the DRC has fewer than two doctors per 10,000 population, compared to over 31 per 10,000 in the UK. Clinics are scarce, often remote, and understaffed, limiting access for affected individuals. Second, local laboratories primarily test for common pathogens like malaria, dengue, or Chikungunya. If common causes are ruled out, rarer pathogens require advanced diagnostics like gene sequencing. In that case, samples may need to be sent abroad for analysis, which can take time. Finally, not all infected people seek medical care, leading to underreporting.

An interesting question is whether this particular outbreak qualifies to be called a Disease X, i.e. the pathogen is unknown and capable of causing a global pandemic. As noted above, most outbreaks are caused by known pathogens, and the reason why the cause has not yet been identified may be due to the difficult medical conditions described in the previous paragraph preventing rapid analysis.

In summary, the Disease X outbreak in Congo presents a significant public health challenge. While the cause and transmission methods remain unclear, health authorities are actively working to investigate the disease and provide support to affected communities. The outbreak appears to be primarily affecting young children who are already suffering from malnutrition, highlighting the vulnerability of this population. The remote location and limited healthcare access in the affected region further complicate the situation. More generally, without significant improvements in global disease surveillance and response mechanisms, outbreaks like Disease X could escalate into global pandemics before being detected and managed effectively. It remains to be seen whether this particular disease outbreak is being caused by an unknown pathogen.

Postscript (NPR):

“On December 27, WHO announced the results from 430 samples: The outbreak was caused by a familiar enemy — or, more accurately, multiple familiar enemies. Patients had acute respiratory infections — think COVID, flu or rhinoviruses — complicated by malaria as well as widespread malnutrition.”

In summary, The Congo Disease X was not caused by a new pathogen (as was suspected), and instead was the result of multiple familiar pathogens.

Figure 1. Doctors and healthcare professionals are working around the clock to contain "Disease X" in Congo. At this time the cause is unknown, despite over 100 deaths mostly among young children.