This Sunday I had nice discussion with Dr Sameer Agarwal our close relative and a senior Pathologist from Jaipur and he showed me some papers on the role of leaf extract from Papaya curing/ improving platelet counts. I have read as Botanist that many latex bearing plants are used in traditional medicine to cure different ailments . Day long we discussed on the mechanism of enhancement of platelet counts in patients in Malaysia . In Malaysia, many people take papaya leave juice to increase platelet count when they get dengue fever. It’s a fact that, to date, there’s no known medical cure for dengue fever since it’s caused by a virus transmitted through the bite of the Aedes mosquito. However, it seems drinking papaya leaf extract helps to bring up the platelet count. Dengue virus infection causes apoptosis and cell death. Clinically there's a marked fall in platelet count. 
Q. Does the NS3 serine protease of dengue virus has a role in causing apoptosis in megakaryoctes and hence reduction of platelets. 

 The leaf extract of papaya is used in folk medicine to increase platelet count in dengue fever. A study has also been done.(thrombocyte count_mice_papaya_leaf.png). 

 Hypothesis Do cysteine proteases of papaya leaves inhibit or alter the apoptotic activity of NS3 serine protease of dengue virus? The cysteine proteinases, serine proteases, calpians and cathepseins (papain superfamily), groups of enzymes display strong homology. 

They appear to act putatively in opposed manner. Probably minor structural differences between these enzymes may explain the apparent contradiction. Future research should address the structural differences between mammalian, viral and plant proteinases and there interplay with emphasis on there role in apoptosis also. 
There is also a mention of the pennywort leaves (locally known as “daun pegaga” or “valarai” in Tamil) having the same effect. Read more on local plants and its effects Sources: http://www.chemocare.com, http://HealthAtoZ.com 
(Compiled based on discussion with Dr Sameer Agarwal, MBBS, M.D.(Pathology) senior pathologist Jaipur).