Physical factors can influence vectors of disease such as the prevalence of mosquitoes in warm, humid areas close to water sources.
Many diseases such as malaria, yellow fever, sleeping sickness and dengue fever depend on the warm conditions of the tropics and sub-tropics.
Seasonal temperature variations in a location often cause seasonal variations in disease rates also.
Climate change provides the conditions for emerging infectious diseases to spread to new places and new hosts such as West Nile virus, tsetse fly and tick seasons.

Bacteria:

Bacteria have optimal growth conditions under which they thrive, but once outside of those conditions the stress can result in either reduced or stalled growth, dormancy or death.
Depending on the temperature, bacteria can be classified as: psychrophiles, which survive below temperatures of 20°C; mesophiles, which survive between temperatures of 20°- 45°C; and thermophiles, which survive between temperatures of 45° - 60°C.
Optimal acidity for bacteria tends to be around pH 6.5 to 7.0.

Viruses and Parasites:

Because viruses and parasites need to infect the cells of a host in order to survive, physical factors are less influential.

Air-Borne:

Rainfall, mean of sunshine daily hours, latitude and altitude are all important physical factors.
Infrequent or exceptional extreme events also influence the spread of airborne diseases, such as tropical storms, hurricanes, typhoons or monsoons.
The spread of disease through the air could also arguably be more of a socio-economic factor (i.e. proximity of people), although the relative remoteness or isolation of a place due to extreme temperatures or relief is a key physical factor in limiting the spread of disease.

Water-Borne:

Precipitation and water sources have a direct impact on the spread of disease through water.
In the tropics precipitation is seasonal, meaning that pools of water can only form during the wet season. This controls the mosquito population and the spread of malaria.
Flooding after heavy rains can result in sewage overflow and widespread water contamination.
The dependence on water means that many diseases remain in lowland altitudes.

Vector-Borne:

As explained above, physical factors will determine the prevalence of the host (rather than the disease), including mosquitoes and ticks.

Global Patterns of Disease