Rickettsia are small, non-motile, obligate intracellular bacteria and are not classified as true bacteria but are considered transitional between bacteria and viruses. Rickettsiae are responsible for various diseases, including typhus and spotted fevers. The shape of *Rickettsia*, the genus of bacteria that causes typhus, can vary depending on the species:

1. *Bacillary Form:* Some *Rickettsia* species, such as *Rickettsia prowazekii* (the agent of epidemic typhus), and *Rickettsia typhi* (the agent of endemic or murine typhus), exhibit a bacillary or rod-shaped form. In this形态，它们可以在微观下显示为短而直的细菌。

2. *Ovoid or Coccobacillary Form:* Other *Rickettsia* species, such as *Rickettsia rickettsii* (the agent of Rocky Mountain spotted fever) and *Rickettsia akari* (the agent of rickettsialpox), appear ovoid or coccobacillary in shape. They are short and oval or spherical.

It's essential to note that *Rickettsia* are generally characterized by their small size, typically ranging from 0.3 to 1.0 microns in length, and they cannot be visualized using a traditional light microscope alone. Advanced techniques, including electron microscopy and molecular diagnostics, are necessary to study and identify *Rickettsia* properly.