Typhus overview

# Overview
Typhus a group of diseases caused by louse-borne bacteria. The name comes from the Greek typhos, meaning smoky or lazy, describing the state of mind of those affected with typhus. Rickettsia is endemic in rodent hosts, including mice and rats, and spreads to humans through mites, fleas and body lice.  The arthropod vector flourishes under conditions of poor hygiene, such as those found in prisons or refugee camps, amongst the homeless, or until the middle of the 20th century, in armies in the field. In tropical countries, typhus is often mistaken for dengue fever.

# Historical Perspective
The first description of typhus was given in 1083 at a convent near Salerno, Italy. In 1546, Girolamo Fracastoro, a Florentine physician, described typhus in his famous treatise on viruses and contagion, De Contagione et Contagiosis Morbis. Before a vaccine was developed in World War II, typhus was a devastating disease for humans and has been responsible for a number of epidemics throughout history. These epidemics tend to follow wars, famine, and other conditions that result in mass casualties. The first reliable description of the disease appears during the Spanish siege of Moorish Granada in 1489. These accounts include descriptions of fever and red spots over arms, back and chest, progressing to delirium, gangrenous sores, and the stink of rotting flesh. During the siege, the Spaniards lost 3,000 men to enemy action but an additional 17,000 died of typhus. Typhus was also common in prisons (and in crowded conditions where lice spread easily), where it was known as Gaol fever or Jail fever. Gaol fever often occurs when prisoners are frequently huddled together in dark, filthy rooms. Imprisonment until the next term of court was often equivalent to a death sentence. It was so infectious that prisoners brought before the court sometimes infected the court itself. Following the Assize held at Oxford in 1577, later deemed the Black Assize, over 300 died from Epidemic typhus, including Sir Robert Bell Lord Chief Baron of the Exchequer. The outbreak that followed, between 1557 to 1559, killed about 10% of the English population.

# Classification
Typhus is a  group of diseases caused by bacteria that are spread to humans by fleas, lice, and chiggers. Typhus fevers include scrub typhus, murine typhus, and epidemic typhus. Chiggers spread scrub typhus, fleas spread murine typhus, and body lice spread epidemic typhus. The most common symptoms are fever, headaches, and sometimes rash.

# Pathophysiology
Typhus is a zoonotic disease, humans are infected by the bites from parasites such as fleas, lice, mites, and ticks or by the inoculation of infectious fluids or feces from the parasites into the skin. The incubation period of Typhus fever varies from one to two weeks. Following transmission, rickettsia are ingested by macrophages and polymorphonuclear cells. The major pathology is caused by a vasculitis and its complications. This process may cause result in occlusion of blood vessels and initiates an inflammatory response (aggregation of leukocytes, macrophages, and platelets) resulting in small nodules. This vasculitic process causes destruction of the endothelial cells and leakage of the blood leading to volume depletion with subsequent hypovolemia and decreased tissue perfusion and, possibly, organ failure.

# Causes
Typhus is caused by one of two types of bacteria Rickettsia typhi or Rickettsia prowazekii. The form of typhus depends on which type of bacteria causes the infection. Rickettsia typhi causes murine or endemic typhus. Endemic typhus is uncommon in the United States. It is usually seen in areas where hygiene is poor and the temperature is cold. Endemic typhus is sometimes called "jail fever." Murine typhus occurs in the southeastern and southern United States.

# Differentiating Typhus from other Diseases
Typhus must be differentiated from other diseases that cause fever, rash, diarrhea and vomiting, such as Ebola, Typhoid fever, Malaria and Lassa fever.

# Epidemiology and Demographics
The Centers for Disease Control and Prevention have documented only 47 cases from 1976 to 2010. According to the World Health Organization, the case fatality rate from typhus is about 1 out of every 5,000,000 people per year. All age groups are at risk for rickettsial infections during travel to endemic areas. The typhus group of infections has no sexual predilection. Scrub typhus, which is transmitted by mites encountered in high grass and brush, is endemic in northern Japan, Southeast Asia, the western Pacific Islands, eastern Australia, China, maritime areas and several parts of south-central Russia, India, and Sri Lanka. R. typhi and R. felis, which are transmitted by fleas, are widely distributed, especially throughout the tropics and subtropics and in port cities and coastal regions with rodents.

# Diagnosis

## History and Symptoms
Signs and symptoms of typhus usually appear abruptly, 816 days following exposure to infected lice. Illness can vary from mild to severe, and even life-threatening. Symptoms of acute infection are generally non-specific and include fever and chills, headache, rapid breathing, myalgia, rash, cough, nausea, vomiting and altered mental status.

## Physical examination
Typhus presents with high-grade fever and a maculopapular rash. Generalized lymphadenopathy is present in majority of the patients. Physical examination usually reveals a combination of several non-specific findings.

## Laboratory findings
Diagnosis of typhus is usually based on clinical recognition and serology, the latter requires comparison of acute- to convalescent-phase serology, so is only helpful in retrospect. Etiologic agents can generally only be identified to the genus level by serologic testing. PCR and immunohistochemical analyses may also be helpful.

## Other diagnostic studies
There is no specific X-ray, CT or MRI finding associated with typhus.

# Treatment

## Medical Therapy
Treatments for most rickettsial illnesses are similar and include administration of appropriate antibiotics (e.g., tetracyclines, chloramphenicol, azithromycin, fluoroquinolones, and rifampin) and supportive care. Treatment should usually be given empirically prior to disease confirmation, and the particular antimicrobial agent and the length of treatment are dependent upon the disease and the host.

## Surgery
Surgical intervention is not recommended for the management of typhus.

## Primary Prevention
No licensed vaccines for prevention of rickettsial infections are commercially available in the United States. With the exception of the louse-borne diseases, for which contact with infectious arthropod feces is the primary mode of transmission (through autoinoculation into a wound, conjunctiva, or inhalation), travelers and health-care providers are generally not at risk for becoming infected via exposure to an ill person. Limiting exposures to vectors or animal reservoirs remains the best means for reducing the risk for disease. Travelers should be advised that prevention is based on avoidance of vector-infested habitats, use of repellents and protective clothing, prompt detection and removal of arthropods from clothing and skin, and attention to hygiene.