Protothecosis, otherwise known as Algaemia, is a disease found in dogs, cats, cattle, and humans caused by a type of green alga known as Prototheca that lacks chlorophyll and enters the human or animal bloodstream. It and its close relative Helicosporidium are unusual in that they are actually green algae that have become parasites. The two most common species are Prototheca wickerhamii and Prototheca zopfii. Both are known to cause disease in dogs, while most human cases are caused by P. wickerhami. Prototheca is found worldwide in sewage and soil. Infection is rare despite high exposure, and can be related to a defective immune system. In dogs, females and Collies are most commonly affected.The first human case was identified in 1964 in Sierra Leone. Cause
Prototheca has been thought to be a mutant of Chlorella, a type of single-celled green alga. However, while Chlorella contains galactose and galactosamine in the cell wall, Prototheca lacks these. Also, Chlorella obtains its energy through photosynthesis, while Prototheca is saprotrophic, feeding on dead and decaying organic matter. When Prototheca was first isolated from slime flux of trees in 1894, it was thought to be a type of fungus. Its size varies from 2 to 15 micrometres. Treatment
Treatment with amphotericin B has been reported. In cattle
Cattle can be affected by protothecal enteritis and mastitis. Protothecal mastitis is endemic worldwide, although most cases of infected herds have been reported in Germany, the United States, and Brazil. In dogs
Disseminated protothecosis is most commonly seen in dogs.
Presently the bacteria most often causing infection are Streptococcus pneumoniae, Streptococcus pyogenes, or Staphylococcus aureus.Alternate risk factors and causes associated with infection include burns and other trauma to the area. Medical research has also identified a link between epiglottitis and crack cocaine usage. Underlying health conditions, such as Graft-versus-host disease and Lymphoproliferative disorders, have also been identified as contributors of increased risk for developing the infection . This is in part caused by the hosts decreased immune response coupled with the common sites targeting the soft tissue of the lymphatic system, both of which are already negatively impacted by the pre-existing illnesses. Diagnosis
Diagnosis may be confirmed by direct inspection using a laryngoscope, although this may provoke airway spasm. If epiglottitis is suspected, attempts to visualise the epiglottis using a tongue depressor are discouraged for this reason; therefore, diagnosis is made on basis of indirect fiberoptic laryngoscopy carried out in a controlled environment like an operating room. Imaging is rarely useful, and treatment should not be delayed for this test to be carried out. Imaging
On lateral C-spine X-ray, the thumbprint sign describes a swollen, enlarged epiglottis. A normal X-ray, however, does not exclude the diagnosis. An ultrasound may be helpful if specific changes are present, but its use (as of 2018) is in the early stages of study.On CT imaging, the "Halloween sign" describes an epiglottis of normal thickness. It can safely exclude the acute epiglottitis. Furthermore, CT imaging can help to diagnose other conditions such as peritonsillar abscess or retropharyngeal abscess which have similar clinical features.