The biggest health threat I experienced when there was the risk of contracting diseases transmitted by mosquitoes. Brazil has a tropical climate and the mosquito population is tremendous.
The key tip is to protect yourself against mosquito bites since some diseases transmitted by mosquitoes such as malaria and zika virus have no vaccines. Always use mosquito repellant.
Mosquito-transmitted diseases with vaccines are;
Yellow fever.
Dengue.
It is not a requirement that you get these vaccines before heading to Brazil but safety first!
Typhoid is also common here, luckily the vaccine available.
Further tips for your healthcare safety.
If you can get your medical insurance provider to cover you even when outside your country, that'll be great.
IMPORTANT:Expectant women should avoid visiting Brazil as they are more susceptible to the Zika virus if you have to visit, always stay in a cool or air-conditioned environment.