The first “extensively drug-resistant” strain of typhoid is spreading through Pakistan, leaving scientists concerned about a deadly outbreak and the rise of other drug-resistant diseases.

Five different types of antibiotics have proven ineffective against the new strain, which has infected 850 people across Pakistan, according to the New York Times. Only one known antibiotic remains effective against it, according to the Independent. But one more mutation, and the disease could become altogether untreatable.

Typhoid is spread through food or water contaminated with the feces of a typhoid-infected person. Case mapping shows that the outbreak of the new strain originated in Hyderabad, Pakistan, along the city’s sewage lines, which may have leaked into water sources, the Times reports.

Take Action: No One Should Suffer From Diseases We Know How to Treat or Prevent

Typhoid causes high prolonged fever, headache, and vomiting, among other symptoms, and can be fatal if left untreated. Approximately 21 million cases and 222,000 typhoid-related deaths occur worldwide every year, according to the World Health Organization (WHO). Four deaths in Pakistan from this particular strain have been confirmed so far and one travel-related case in the United Kingdom, the New York Times reports.

Experts expect the drug-resistant strain to eventually spread worldwide.

Two typhoid vaccines currently exist, according to the WHO, but low vaccination rates in countries like Pakistan paired with poor sanitation infrastructure means that typhoid is still endemic to many areas of the world.

Read More: This Australian Organisation is Working to Eradicate this Preventable Disease for Good

The typhoid strain’s emergence is an alarming development in the trend of one of global health’s greatest growing threats: drug-resistant illnesses.

“This isn’t just about typhoid,” Dr. Rumina Hasan, a pathology professor at the Aga Khan University in Pakistan, told the New York Times. “Antibiotic resistance is a threat to all of modern medicine — and the scary part is, we’re out of options.”

In a September 2017 report, the WHO identified 12 classes of “priority pathogens” — including typhoid and tuberculosis — “that are increasingly resistant to existing antibiotics and urgently in need of new treatments.” The report also found that, of the 51 antibiotics being developed to treat drug-resistant strains of diseases, only eight could be classified as “innovative treatments that will add value to the current antibiotic treatment arsenal.”

"Antimicrobial resistance is a global health emergency that will seriously jeopardize progress in modern medicine," Dr. Tedros Adhanom Ghebreyesus, Director General of the WHO, said in a statement when the report was published.

Global Citizen campaigns on vaccination efforts around the world. You can take action here.