A bacterial zoonosis

The plague is a bacterial zoonosis caused by Yersinia pestis, discovered in 1894 by Alexandre Yersin. It is transmitted from one animal to another by fleas. Humans can also become infected and transmit the disease.
The plague can be fatal in humans, but antibiotic treatment is effective in most cases if administered early.
The three main endemic countries are currently Madagascar, the Democratic Republic of the Congo, and Peru. France is particularly attentive to the plague situation in Madagascar, given the proximity of Réunion and Mayotte. Mandatory
reporting of this disease should make it possible to identify the source of infection in a case detected on national territory and to implement preventive measures early among contacts to limit the risk of the disease spreading.

In this context, Santé publique France’s priorities are:

• Detecting as early as possible any cases occurring in the country, given that the disease does not occur naturally in France,

• Where applicable, the investigation of individual cases or clusters of cases

• Informing healthcare professionals and public authorities.

An animal disease transmissible to humans

Yersinia pestis is usually found in small mammals and the fleas that parasitize them. Rodents are the most important animal reservoirs, but other animals such as cats, dogs, rabbits, and hares can also become infected.
The plague is transmitted between rodents and to other animals via rodent fleas.

Humans can become infected:

• Through bites from infested fleas;

• Through direct, unprotected contact while handling infected animals or contaminated biological materials;

• By inhaling respiratory droplets containing bacteria emitted when a patient with pneumonic plague coughs.

Essential preventive measures

Pest prevention relies on:

• Controlling flea bites and rodent infestations in regions where the plague is prevalent,

• Protective measures against droplets emitted when a patient with pneumonic plague coughs (wearing a mask).

For healthcare workers treating plague cases, individual and collective precautions (gloves, masks, protective eyewear, surface cleaning) help prevent transmission.
For people who have been in contact with a confirmed case of plague, antibiotic treatment will be administered as soon as possible to prevent the development of infection.
There is no commercially available vaccine for humans.

Three clinical forms

The plague primarily presents in three clinical forms:

Bubonic plague:

It follows a bite from an infected flea. The incubation period is 1 to 7 days. It manifests as the sudden onset of fever, chills, a deterioration in general health, and painful swollen lymph nodes (buboes) in the area where the flea bit. Without treatment, the bacteria can spread throughout the body, and 50 to 60% of patients with untreated bubonic plague die; early initiation of appropriate antibiotic treatment is crucial for improving the prognosis. This clinical form is not directly contagious from person to person unless there is direct contact with the pus from the buboes.

Pneumonic plague:

It can result from a direct infection of the respiratory system through inhalation of droplets containing bacteria (primary pneumonic plague) or from bacterial colonization of the lungs following dissemination of the bacteria in the bloodstream (secondary pneumonic plague). The incubation period is 1 to 4 days. It presents with fever, headache, a general feeling of malaise, and rapidly progressing pneumonia with shortness of breath, chest pain, and cough, with or without the production of blood-streaked sputum. It can lead to respiratory failure and shock. Without treatment, this form is usually fatal; early initiation of appropriate antibiotic therapy is crucial for improving the prognosis. This form is highly contagious from person to person and requires strict isolation and respiratory protection measures to prevent secondary cases.

Septicemic plague:

This form results from the spread of the bacteria into the bloodstream. It most often follows bubonic plague but can be the first manifestation of the disease. It presents with the sudden onset of high fever, chills, and a general feeling of malaise with abdominal pain, followed by the rapid and progressive failure of multiple organs (heart, kidneys, liver). This form can lead to meningitis, shock, or disseminated intravascular coagulation: the skin and other tissues may turn black, especially on the fingers, toes, and nose. Without treatment, this form is invariably fatal; early initiation of appropriate antibiotic therapy is critical for improving the prognosis. However, mortality among treated septicemic cases remains high, at around 40 to 50%. This clinical form is not directly contagious from person to person unless it follows a bubonic form and there is direct contact with pus from the buboes.

Confirmation of the diagnosis of plague relies on the identification of Y. pestis in a sample of pus from a bubo, in the blood, or in sputum. Various techniques can detect a specific antigen of the bacillus. Rapid tests (“test strips”) exist, but their use must strictly follow the manufacturer’s instructions to obtain a reliable result (risk of false positives and false negatives). Rapid tests are used primarily during epidemics, and their results must be confirmed by a more robust test (bacterial identification or PCR) performed in a specialized laboratory. Final confirmation may take 24 to 48 hours.
Treatment should be initiated as soon as clinical suspicion arises and after samples have been collected.

Treatment

Plague can be effectively treated with antibiotics (streptomycin, tetracyclines, and fluoroquinolones) provided they are administered early. Plague remains a serious disease with a high fatality rate.
In cases of clinical suspicion of plague in a person, that person must be hospitalized and treatment initiated as quickly as possible, after bacteriological samples have been taken but before the results are available.
Anyone suspected of having pneumonic plague must be isolated with respiratory protection measures to prevent the occurrence of secondary cases.