Ornithonyssus bacoti bacoti is a hematophagous parasite commonly referred to as the tropical rat mite. They feed only on blood and serum from many hosts. They can be found and cause disease on rats and wild rodents most commonly, but also small mammals and humans when other hosts are scarce. Outbreaks tend to occur in older, less maintained buildings. The mite however can travel several hundred feet on its own if necessary to find a host and can survive for extended periods of time without a host. This along with the nonspecific dermatitis it causes can prevent accurate and fast diagnosis of rat mite dermatitis. The scarcity of reports, due in part to misdiagnosis and also the mildness of its symptoms, makes the disease seem less common than it is. The tropical rat mite can be found in both temperate and tropical regions or rather all continents except the arctic and Antarctic.
The tropical rat mite was first reported in Australia in 1913 in a human case report. 1923 marked the United States’ identification of it as a cause of dermatitis in humans. In 1931 it was discovered in Hamburg, Germany in a seaport.
The tropical rat mite is between .75 and 1.44 mm in length and is nonsegmented with chelicerae or mandibles which are suited to piercing. They have a sharp caudal apex of the scutum, an oval genital shield and a cranially positioned anus. These mites are capable of parthenogenic reproduction. After taking a blood meal they are static and yellow or dark red in color. However, before a blood meal they are more active and grey in color.