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Abstract Background An outbreak of Plasmodium malariae infection among forest goers in Sanya City of Hainan Island, China was reported in 2015. In response to this outbreak, an innovative three-layer strategy (TLS) targeted forest goers was adapted based on the 1-3-7 approach. Main text Key elements of TLS are: (i) The village with five malaria cases and adjacent villages were set as the first layer. All residents including forest goers were taken as the high-risk population (HRP). Active case detection (ACD) by blood smear microscopy and PCR was selected as the primary measure, and passive case detection (PCD) as complementary measure. One case was identified under TLS implementation. (ii) The township with cases (Gaofeng Town) and the nearby towns were chosen as the second layer. Only forest goers were screened by ACD, while PCD as a routine screening method. 7831 blood smears collected by ACD and PCD and tested with negative results. (iii) The city with cases (Sanya City) and others 12 counties/county-level cities were selected as the third layer. Malaria cases were monitored passively. A total of 77,555 blood slides were screened by PCD with zero positive sample. For each layer, the malaria vector mosquitoes were monitored using light traps, cattle-baited/human-bait traps. Anopheles minimus (dominant species), An. sinensis and An. dirus were captured. Vector control measures mainly include insecticide residual spraying and long-lasting insecticide nets. The capacity of clinicians, public health practitioners and laboratory technicians has been improved through training. During 2016‒2018, TLS and chemoprophylaxis were implemented in the same areas. In the first layer, all residents were monitored by ACD, and malaria chemoprophylaxis were distributed, 89.5% of forest goers were using chemoprophylaxis against malaria. The blood smears (3126 by ACD plus 1516 by PCD) were with zero positive results. Chemoprophylaxis and ACD were offered to forest goers once a year, and PCD in residents as a complementary measure in the second and third layer, 77.8% and 95.1% of forest goers received chemoprophylaxis. In each layer, vector surveillance and control of malaria and trainings for medical staff were still in place. Conclusions TLS was effective in blocking the outbreak by P. malariae among forest goers in Hainan in malaria elimination stage. However, whether it could prevent the malaria resurgence in the post-elimination phase needs to be further assessed. Graphical Abstract

The distribution of chlorophyll-a (Chl-a) in the Yangtze River Mouth area was analyzed using a new Chl-a inversion model (PMS-C) based on the relationship between in situ Chl-a and GF-4 PMS band combinations. Combining GF-4 PMS with HY-C CZI, this paper revealed that: (1) Chl-a concentration in Yangtze River Mouth was in the range of 2–6 µg/L, being higher in the west than in the east. The high Chl-a area was mainly distributed near the mouth of the Yangtze River and the Chl-a value was in the range of 3.7 µg/L to 5.9 µg/L. Chl-a concentration is higher in spring and summer than in autumn and winter, with a Chl-a concentration difference of 1–2 µg/L. Chl-a downstream of islands and bridges increased by 0.5–1.7 µg/L compared with upstream. (2) Short-term (within 3 h) changes of Chl-a concentration were effectively detected. In summer and autumn, Chl-a obtained at 13:30 in the noon was generally lower than Chl-a obtained at around 10:30 in the morning and it decreased by nearly 0.1–4 μg/L within three hours on the same day. In winter, the concentration of Chl-a decreased in the range of 0–1.9 μg/L. Generally, within three hours, Chl-a in the downstream of the island decreased significantly from 5 μg/L to about 3.8 μg/L, and Chl-a downstream of piers decreased from 3.7 μg/L to about 3 μg/L. (3) Environmental factors including seawater temperature, illumination, and nutrients, as well as dynamic factors such as wind and tidal current can induce Chl-a change in the Yangtze River Mouth. Short-term change of Chl-a concentration is closely related to the specific hydrodynamic conditions, nutrients, and lighting conditions.

Hainan Province is in a tropical area of China and previously experienced serious P. falciparum and P. vivax malaria epidemics. After nearly 70 consecutive years of malaria prevention and control, malaria in Hainan has gradually been eliminated. To achieve the elimination of malaria, Hainan enacted six stages: investigative research and pilot prevention and control, large-scale antimalaria measures, adjustment of strategies for prevention and control, joint prevention and control measures, global funding of routine malaria control, and malaria elimination. Different strategies for malaria control were adopted at different stages. Malaria was most prevalent in the mountainous areas of central and southern Hainan, which contain a high-risk population (the forest goers) and two highly effective malaria vectors (An. dirus and An. minimus). Forest goers have been a high-risk population for malaria in Hainan since their identification in the 1990s. This paper summarizes malaria monitoring in forest goers and the response of forest goers to malaria control and elimination, distilling specific malaria control and elimination measures via case studies in Hainan Province. Two case studies in the malaria control stage demonstrated different measures for outbreaks and sporadic cases in forest goers. In view of the malaria outbreak in Sanya during the elimination stage, three-layered strategies (TLSs) were implemented to control outbreaks and improve control measures. Moreover, this paper also illustrates specific management measures to prevent malaria retransmission from sporadic imported malaria cases during the elimination phase. Hainan finally eliminated malaria in 2020. However, the risk of malaria retransmission is still high due to the prevalence of effective malaria vectors in Hainan, and forest goers are still a high-risk population for malaria retransmission. [ABSTRACT FROM AUTHOR]