Date Published: April 26, 2018
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Xuan Zhang, Linong Yao, Jimin Sun, Jinren Pan, Hualiang Chen, Lingling Zhang, Wei Ruan.
To study the epidemiological distribution and the incident trends of imported malaria from 2012 to 2016 in Zhejiang Province, southeastern China, we collected data on malaria from the Information System for Parasitic Disease Control and Prevention. A total of 1,003 malaria cases were reported during 2012–2016, and all of these cases were imported. Plasmodium falciparum was the predominant species (76.3%) in Zhejiang Province. The percentage of Plasmodium vivax decreased from 33.6% to 8.1%, whereas the percentage of Plasmodium ovale and Plasmodium malariae increased. Most cases were male (89.8%), mostly in the age group of 21–50 years (82.6%). Businessmen (33.0%), workers (21.0%), farmers (18.8%), and overseas laborers (11.7%) were at high risk. The origin of the largest number of imported cases was Africa (89.5%), followed by Asia (10.0%) and Oceania (0.5%). The time interval from illness onset to confirmation was found to be significantly associated with the complications of patients. Out of 3,461 febrile individuals tested during reactive case detection, 10 malaria-positive individuals were identified. Effective surveillance and response system should be strengthened to prevent the reintroduction of malaria.
Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. It remains one of the major public health problems in the world. According to the estimation by the World Health Organization, 91 countries and territories had ongoing malaria transmission in 2015, and about 32 billion people (nearly half of the world’s population) were at risk of malaria. There were 212 million cases of malaria and 429,000 deaths worldwide in 2015.1 China has made progress in controlling locally transmitted malaria over the past decades, which led to a dramatic decrease in the incidence of malaria. The total malaria incidence rate in China had reduced to 1.06/100,000 in 2009.2 Since 2010, China has initiated the National Malaria Elimination Program, aiming to eliminate indigenous malaria except for border areas by 2015 and achieve malaria elimination nationwide by 2020.3
During the period of 2012–2016, a total of 1,003 malaria cases were identified and reported in Zhejiang Province (Figure 1). All of these cases were imported from other provinces of China or other countries. Plasmodium falciparum was the predominant species, which accounted for 76.3% (765/1,003) of the total malaria cases, and the percentage peaked in 2014 to 80.5%. Of note, two patients died of P. falciparum in 2013 and 2016. The percentage of Plasmodium vivax decreased significantly from 33.6% in 2012 to 8.1% in 2016 (χ2 = 40.259, P < 0.001), whereas the percentage of Plasmodium ovale increased significantly from 1.4% in 2012 to 10.6% in 2016 (χ2 = 11.080, P < 0.001) and the percentage of Plasmodium malariae increased from 0.5% in 2013 to 2.4% in 2016 (χ2 = 2.847, P > 0.05). Moreover, six imported cases were due to relapsing P. vivax and P. ovale that had been acquired several months up to about 2 years before. Mixed infections with two species were also reported in the past 5 years, which accounted for 1.2% of all malaria cases.
Historically, P. vivax has been the predominant Plasmodium species in Zhejiang Province,4 but now P. falciparum is the predominant species, and P. vivax cases declined dramatically. This situation is similar to the Plasmodium species distribution in China,6 where the local malaria situation has been effectively controlled and indigenous cases decreased sharply.