The 18 victims were among 557 reported cases of suspected human granulocytic anaplasmosis (HGA) since May 2007. Most of the cases were found in Xinyang's Shangcheng and Guangshan counties and Shihe and Pingqiao districts, said the provincial Public Health Department in a statement.

The disease is often reported from May to August and most people infected are between ages 40 to 70, according to officials.

To probe the cause of the disease, the Chinese Center for Disease Control and Prevention (CDC) ordered Henan CDC to start monitoring the disease on May 31, said Xu Bianli, deputy head of Henan provincial CDC.

Henan CDC sent experts to Xinyang to help local doctors diagnose with the disease and contain its spread from April to June.

Doctors at local medical clinics lacked knowledge of the disease as it was only identified in 2007, Xu told Xinhua. Monitoring of the disease is still underway in Xinyang.

HGA reduces white blood cell and platelet counts in the blood, leading to organ failure and death. People in close contact with the patient can also be infected if no precautions are taken.

The disease is curable if treated soon enough.