Hantavirus infection overview

# Overview
Hantavirus infection is a zoonotic disease transmitted by rodents and caused by hantaviruses belonging to bunyaviridae family. The symptoms of hantavirus infection may include sudden fever, prostration, myalgias, and abdominal discomfort. Pulmonary and hemorrhagic symptoms may also arise in severe disease. The three major clinical entities caused by hantaviruses include hantavirus cardiopulmonary syndrome (HCPS), hemorrhagic fever with renal syndrome (HFRS) and nephropathia epidemica (NE). Diagnosis of hantavirus infection is usually made by a positive serological test result.  Evidence of viral antigen in tissue by immunohistochemistry, or the presence of amplifiable viral RNA sequences in blood or tissue, with a compatible history of HPS, is considered diagnostic for HPS. Hantavirus infection must be differentiated from other disease based on hemorrhagic fever such as dengue, malaria and Ebola and based on the cardiopulmonary involvement such as seen in histoplasmosis, coccidioidomycosis, brucellosis, tuberculosis and aspergillosis. The most potent risk factor in the development of hantavirus infection is the exposure to rodent excreta and close contact with hantavirus-infected humans. If left untreated hantavirus infection may cause multiple organ failure and death. The overall prognosis of hantavirus infection depends on the typer of clinical syndrome. The hantavirus cardiopulmonary syndrome (HCPS) has 38% mortality rate. Depending upon which virus is causing the HFRS, death occurs in less than 1% to as many as 15% of the patients. There is no specific treatment, cure, or vaccine for hantavirus infection. However infected individuals who are recognized early and receive medical care in an intensive care unit, may do better. Prevention of hantavirus infection includes indoor and outdoor measures.

# Historical Perspective
HFRS was first clinically recognized in northeast China in1931. In 1976, Lee isolated the first pathogenic hantavirus along the Hantaan River, in South Korea and named it the hantaan virus (HTNV) in1978.

# Classification
Hantavirus infection can be classified on the basis of the clinical manifestations and the type of hantavirus responsible for the manifestation. The clinical manifestations may include hantavirus cardiopulmonary syndrome (HCPS), hemorrhagic fever with renal syndrome (HFRS) and nephropathia epidemica (NE).

# Pathophysiology
Hantavirus is usually transmitted via the inhalation of aerosolized viral antigens or rodent bites. The incubation period of hantavirus infection is of 9 to 33 days. Following inhalation, the virus replicates in pulmonary macrophages and dendritic cells. The primary target cells of hantavirus infection are endothelial cells of capillaries. Infection is followed by impairment of the barrier function of endothelial cells, fluid extravasation, and subsequent organ failure.

# Causes
Hantaviruses belong to the bunyaviridae family of viruses. There are 5 genera within the bunyaviridae family: bunyavirus, phlebovirus, nairovirus, tospovirus, and hantavirus. Each is made up of negative-sensed, single-stranded RNA viruses. All these genera include arthropod-borne viruses, with the exception of hantavirus, which is a genus of rodent-borne agents.

# Differentiating Hantavirus from other Diseases
Hemorrhagic fever caused by hantavirus can be differentiated from other disease  such as dengue, malaria and Ebola. The hantavirus cardiopulmonary syndrome can be differentiated from other diseases like histoplasmosis, coccidioidomycosis, brucellosis, tuberculosis and aspergillosis.

# Epidemiology and Demographics
Hantavirus infection has a diverse epidemiology and demographics due to the vast number of viruses classified under hantaviruses. The total number of hantavirus pulmonary syndrome (HPS) cases reported in the United States from 2004-2015 is 323. HPS cases have been reported in 30 states, including most of the western half of the country and some eastern states as well. Over half of the confirmed cases have been reported from areas outside the Four Corners area. The mean age of confirmed HPS cases is 38 years (range: 5 to 84 years).

# Risk Factors
The most potent risk factor in the development of hantavirus infection risk factors is exposure to rodent excreta and close contact with hantavirus-infected humans.

# Screening
There are no screening recommendations for hantavirus infection.

# Natural History, Complications and Prognosis
If hantavirus infection left untreated, it may result in multi-organ failure and death. Possible complications include, acute encephalomyelitis, Pituitary hemorrhage, Glomerulonephritis, Pulmonary edema, acute respiratory distress syndrome, Disseminated intravascular coagulation, Thrombocytopenia, and shock. Its prognosis depends on the extent of the diseases. The hantavirus cardiopulmonary syndrome (HCPS) has 38% mortality rate but, hemorrhagic fever with renal syndrome (HFRS) has a better prognosis with 1 to 15% mortality rate.

# Diagnosis

## History and Symptoms
The symptoms of hantavirus infection may include sudden fever, prostration, myalgia, and abdominal discomfort. Pulmonary and hemorrhagic symptoms may also arise in severe disease.

## Physical Examination
Patients with hantavirus infection usually exhibit prostration. Physical examination of patients with hantavirus infection is remarkable for abdominal discomfort, fever, skin petechia, low blood pressure and abnormal cardiopulmonary examination.

## Laboratory Findings
Diagnosis of hantavirus infection is usually made by a positive serological test result.  Evidence of viral antigen in tissue by immunohistochemistry, or the presence of amplifiable viral RNA sequences in blood or tissue, with a compatible history of HPS, is considered diagnostic for HPS.

## X ray
On x-ray, hantavirus infection may manifest as noncardiogenic pulmonary edema is characterized by alveolar infiltrates.

## CT scan
On CT scan, hantavirus pulmonary syndrome is characterized by ground-glass opacities and interlobular and intralobular septal thickening.

## MRI
There are no MRI findings associated with hantavirus infection.

## Ultrasound
On renal ultrasound, hantavirus hemorrhagic fever with the renal syndrome may show parenchymal edema, increased echogenicity, and decreased corticomedullary differentiation.

## Other Imaging findings
There are no other imaging findings associated with hantavirus infection.

## Other Diagnostic Studies
Additional diagnostic findings can include the histopathological analysis of lymph nodes, spleen, and liver but are rarely used.

# Treatment

## Medical Therapy
There is no specific treatment, cure, or vaccine for hantavirus infection. However, we do know that if infected individuals are recognized early and receive medical care in an intensive care unit, they may do better.

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

## Primary Prevention
Eliminate or minimize contact with rodents in your home, workplace, or campsite. Seal up holes and gaps in your home or garage. Place traps in and around your home to decrease rodent infestation. Clean up any easy-to-get food. Recent research results show that many people who became ill with HPS developed the disease after having been in frequent contact with rodents and/or their droppings around a home or a workplace. On the other hand, many people who became ill reported that they had not seen rodents or rodent droppings at all. Therefore, if you live in an area where the carrier rodents are known to live, try to keep your home, vacation place, workplace, or campsite clean.

## Secondary Prevention
Secondary preventive measures for hantavirus infection are similar to primary prevention.