You will need malaria meds for most of the year. The best thing to do is to consult a travel clinic. They will be far more familiar with the needs of travelers.   Be sure to explain that you will be mostly in rural and very poor areas.

You will be in each place about a month and there are risks in pretty much each place you are going. Hope this will help:

Palenque, Chiapas, Mexico – January

Antigua, Guatemala – February

south of Managua, Nicaragua [3 days]

Lima, Peru – March-April

Buenos Aires, Argentina [1 week]

South Africa – May

Bulembu, Swaziland – June

Nairobi, Kenya – July

Mumbai, India – Aug/Sept

Cambodia – sept/oct

China – Oct/Nov

Hong Kong [5 days]

Note that this itinerary is subject to change!
You need to be flexible and realize that things change and we will follow the Lord’s leading and not necessarily stick to this itinerary.