A drug-resistant strain of typhoid is spreading in Pakistan, infecting over 2000 people in the past 6 months, according to Science. The new XDR (extensively drug resistant) strain of Salmonella typhi is vulnerable to only one oral antibiotic, called azithromycin. Otherwise, only expensive intravenous drugs can fight the strain, and they are too expensive for widespread use in a low-income nation like Pakistan, costing thousands of dollars for each patient.

In February, researchers writing in the journal mBio first called attention to the outbreak, which at the time had spread in Hyderabad, totaling 339 cases. Three antibiotics used to treat typhoid were found ineffective, as well as two classes of drugs meant to treat strains resistant to those antibiotics.

Doctors warn that it is only a matter of time before the strain develops a resistance to azithromycin as well. Once an outbreak like this begins, it is extremely hard to control.

According to Zulfiqar Bhutta, a pediatrician at Aga Khan University in Karachi:

“This is indeed a really alarming situation. I’m not sure what can be done, as the horse has bolted. This will jump boundaries before long.”

A newly-approved vaccine, which works in younger children and lasts longer than older versions, is being widely administered in Pakistan, with funding from the Bill & Melinda Gates Foundation and a Swiss non-profit called Gavi, the Vaccine Alliance.

The first author of the earlier Mbio study, Wellcome Sanger Institute infectious disease geneticist Elizabeth Klemm, said that the XDR strain had apparently developed from another S. typhi strain that was already resistant to multiple drugs, likely thanks to inappropriate use of antibiotics.

“It is significant because it marks the first time we have seen such high levels of drug resistance in typhoid,” according to Klemm.

The new strain took on an additional resistance gene from a plasmid (DNA molecule) that probably transferred from Escherichia coli, says Klemm, a bacteria that itself comes from human waste and often makes its way into polluted water.

Lead author of the mBio study, Aga Khan University microbiologist Rumina Hasan, said that about one in every three blood samples from typhoid patients in her lab contains the new XDR strain. Visitors to Pakistan have already brought the XDR strain back to their home countries, including two travelers from the US. While there is little risk of spreading the disease in countries like the US with effective sewage and water systems, less developed nations could be at risk, according to Eric Mintz, of the US Centers for Disease Control and Prevention.

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