Latvia is an almost not dangerous country, we don't have rattlesnakes, scorpions, earthquakes, mountains. However, there are some dangers one should be aware of while traveling there.
Thieves
In Riga pickpocketing is a general issue: a full trolleybus or a bus, a busy street, you have to take care. Keep your wallet in front pocket of your pants, watch your bags.
Urban trash
A specific subset of humans can be classified as urban trash - they have strong understanding of their home neighborhood and tend to dislike everyone from outside. Avoid them, don't be aggressive, just move away. Police in Riga is close to worthless.
Drunkards
Drinking raises ones self esteem and what was once not possible, now is. One of the highest rates of deaths on roads in Europe are in Latvia. Friday and Saturday nights are probably worse than others. If you are on a bicycle - ride defensively.
Dogs
Dogs are weakly trained compared to civilized ones from Western countries. Most of them on leash, but still way too uncontrolled: "My doggy never bites." Not so many wild dogs, although on the country side some may running on their own. If on bicycle, lifting your feet high is an option. If off bicycle, keep it between you and the barking party. Don't panic, don't run away.
Snakes
One poisonous (European adder) and 2 (or one?) not poisonous (natrix natrix, the other one is probably a lizard without legs).
Ticks
Ticks have been around for a while, but sometimes around 1950's soviets decided to introduce some animals from Siberia for furs. Turned out some of them had ticks that were carrying tick-borne encephalitis. Some others carry Lyme disease. You can get vaccinated against encephalitis, or you can use extensive dosages of insect repellents. No vaccine against Lyme disease.
More ticks are available in deciduous tree forests, in the bushes, less or almost none in pine forests.
If bitten by tick, don't panic: find an emergency room, remove the tiny thing and send it for analysis. Every year some 180 persons get the encephalitis in Latvia, way more get bitten.
Trash
I have lived in Seattle now for 3 years and one thing is extremely pleasant here - dog owners collect after their dogs. Usually not the case in Latvia. Besides that - usual tourist destinations which are not taken care of regularly as well as road sides - are full of junk. Just be careful and don't add some of yours. We are getting better (think US of 50ies with burning rivers, Latvia is WAY cleaner), but it will take some time.
Bears
There are some (20 or so) brown bears in northern and north-eastern regions. There haven't been any reported attacks on humans. If you encounter one, retreat slowly, especially if you see cubs (big angry mama is never far away). There are no other bear regulations like in USA.