I contracted common malaria, vivax?, when i was 20 yrs old from long visit to Papua NewGuinea, 1970. Returned to USA and was treated with chloro, primaquine drugs and really no problems since treatment.
Now going to Thailand for week, Chiang Mai and region. If bitten by local malarial mosq. am i more likely to recur? And should I certainly choose prophylaxis? thnx
If you were treated successfully with chloroquine and primaquine then there is no reason for your malaria to reoccur. Since it has been a long time since you had malaria, you probably also don’t have any antibodies against the parasite in your system anymore; this just means you don’t have any extra immunity against P. vivax (which you might have done if you had returned to a malaria area, and particularly one with the same strain of P. vivax as that which infected you, within a few months or years of being infected the first time), but it doesn’t mean you will be any more susceptible than someone who never had malaria.
In terms of where you are going, the city of Chiang Mai itself is not considered to have malaria transmission, but the areas surrounding it are, particularly as you get closer to the Burmese border. As such, if you will be travelling in rural and/or forested areas, you might want to consider taking prophylactic medication (and other preventative measures, like sleeping under a long-lasting insecticide treated bednet).
Thailand unfortunately has seen the emergence of resistance to a couple widely used prophylactic measures, namely chloroquine and mefloquine (sold as Lariam), so these are not appropriate preventative medicine in this region. Instead, you should consider taking doxycycline or atovaquone-proguanil (sold as Malarone).