Recently an older female pet rat came in my clinic for an exam. The rat was not as active as normal and had lost some weight. On physical exam the rat was indeed thin for her size and had lost a lot of the muscle mass on her rear legs and back. There were also some crusty lesions on her skin. There was a small amount of hair loss and some trauma from her scratching at the skin. Close examination of the skin and hair revealed some movement of the crusty material.
In pet rodents external parasites are common. In mice, mites and lice are frequently seen. In rats, mites are common. The movement in the crusty material made me suspect an external parasite was involved. A small amount of the material was put on a microscope slide with a small amount of oil. A photo of the slide shows that a bug was causing the skin problem. It looks like this rat had the spined rat lice (Polyplax spinulosa) causing its itchy skin problem.
Lice on rats can be treated with several different products, including ivermectin, Frontline, Revolution and Advantage Multi. Lice can transmit some diseases to rats, such as those from Hemobartonella and Rickettsia. These lice are actual blood suckers, so severe infestations can cause anemia in the rat. In general, lice are very species-specific, so humans will not get infected with lice from a rat.
Unfortunately, this rat also had a more serious problem. She was having very labored breathing from pneumonia. Respiratory disease is the most common problem seen in pet rats. Respiratory infections can be caused by both bacteria (such as Mycoplasma and Streptococcus) and viruses (such as Sendai virus and Hantavirus). The most common agent is Mycoplasma.
Mycoplasma infections in rats are frustrating to treat and only rarely cured. Most rats with Mycoplasma will need treatment periodically throughout their life with the antibiotic doxycycline and a bronchodilator (albuterol). Pneumonia is usually caused by Streptococcus pneumoniae along with another agent, such as Mycoplasma or Sendai virus. Treatment with an antibiotic like Clavamox and supportive care with fluids and nutrition can be tried, but even with aggressive treatment some rats will not survive.