  We consider dilute gases of dipolar bosons or fermions in the
high-temperature limit in a spherically symmetric harmonic trapping potential.
We examine the system using a virial expansion up to second order in the
fugacity. Using the Born approximation and assuming purely dipolar
interactions, we find that the second-order virial coefficient for both bosons
and fermions depends quadratically on the dipole length and is negative at high
temperature, indicating that to lowest order in the dipole-dipole interactions
the dipolar single-component quantum gases are repulsive. If the $s$-wave
scattering length for the bosonic system is tunable and its absolute value is
made small, then the $s$-wave interactions dominate and the dipolar as behaves
like a weakly-interacting Bose gas with isotropic $s$-wave interactions. If the
generalized scattering lengths for the fermionic system are tunable, then the
dipole length can enter linearly in the virial equation of state, enhancing the
dipole-dipole effects in the thermodynamic observables.
