Hantavirus pulmonary syndrome
HANTAVIRUS PULMONARY SYNDROME
HANTAVIRUS PULMONARY SYNDROME DEFINITION
Hantavirus pulmonary syndrome (HPS) is a rare but potentially life-threatening viral illness transmitted to humans by inhaling infected rodent urine, droppings or saliva.
HANTAVIRUS PULMONARY SYNDROME CAUSES
Each type of hantavirus has a preferred rodent carrier. The deer mouse is the primary carrier of the virus responsible for most cases of hantavirus pulmonary syndrome in North America. Other hantavirus carriers include the white-tailed mouse, cotton rat and rice rat.
INHALATION: MAIN ROUTE OF TRANSMISSION
Hantaviruses are transmitted to people primarily through the “aerosolization” of viruses shed in infected rodents’ droppings, urine or saliva. Aerosolization occurs when a virus is kicked up into the air, making it easy for you to inhale. For example, a broom used to clean up mouse droppings in an attic may nudge into the air tiny particles of feces containing hantaviruses, which you can then easily inhale.
After you inhale hantaviruses, they reach your lungs and begin to invade tiny blood vessels called capillaries, eventually causing them to leak. Your lungs then flood with fluid, which can trigger any of the respiratory problems associated with hantavirus pulmonary syndrome.
People who have the North American version of hantavirus pulmonary syndrome aren’t contagious to other people. However, the milder South American variety of the disease can be transmitted from person to person.
HANTAVIRUS PULMONARY SYNDROME PATHOPHYSIOLOGY
The basic pathophysiological lesion of HPS, and indeed of all Hantavirus infections, is a generalized increase in capillary permeability that results from endothelial damage. This injury appears to be a consequence of the host’s immunological response to viral antigens that have penetrated the endothelium by means of the cells’ own integrins. The onset of clinical symptoms is correlated with the development of specific antibodies to the virus. The increased capillary permeability gives rise to widespread protein-rich edema. The particular organs affected are related to the specific species of Hantavirus. In HFRS, a large outpouring of edema fluid flows into the retroperitoneum and is associated with hemorrhage and necrosis. Individuals with HPS have edema concentrated in the pleura and lungs.
The endothelial cells appear swollen. Lung examination findings reveal an interstitial pneumonitis made up of edema fluid, mononuclear cells, and lymphocytes with polymorphonuclear leukocytes. Hyaline membranes appear along with a proliferation of type 2 alveolar lining cells. As the disease progresses, the alveolar septa become increasingly fibrotic. The spleen in patients with HPS shows infiltration of immunocompetent cells within the red pulp and the periarteriolar sheaths.
Severe cases of HPS present clinically as noncardiogenic pulmonary edema. The pathophysiology of the pulmonary findings is that of a pulmonary capillary leak syndrome. The heart is not directly affected. The pulmonary capillary leak syndrome is the primary underlying pathophysiological defect responsible for both cardiopulmonary and renal dysfunction. Prerenal azotemia is due to the inadequate intravascular volume of the hypotensive patient and not to direct infection. Hantavirus particles are not found within the renal tubular cells of patients with HPS. Hypoxia also contributes to the state of shock.
HANTAVIRUS PULMONARY SYNDROME SYMPTOMS
Hantavirus pulmonary syndrome advances through two distinct stages. In the first stage, you may experience flu-like signs and symptoms that may include
- Fever and chills
- Headaches and muscle aches
- Vomiting, diarrhea or abdominal pain
In its early stages, hantavirus infection is difficult to distinguish from influenza, pneumonia or other viral conditions. After four to 10 days, more-serious signs and symptoms begin. They typically include:
- A cough that produces secretions
- Shortness of breath
- Fluid accumulating within the lungs
- Low blood pressure
- Reduced heart efficiency
HANTAVIRUS PULMONARY SYNDROME DIAGNOSIS
Diagnosing HPS in an individual who has only been infected a few days is difficult, because early symptoms such as fever, muscle aches, and fatigue are easily confused with influenza. However, if the individual is experiencing fever and fatigue and has a history of potential rural rodent exposure, together with shortness of breath, would be strongly suggestive of HPS. If the individual is experiencing these symptoms they should see their physician immediately and mention their potential rodent exposure.
HANTAVIRUS PULMONARY SYNDROME TREATMENT
Specific treatment options for hantavirus pulmonary syndrome are limited. But the prognosis improves with early recognition, immediate hospitalization and adequate support for breathing.
People with severe cases need immediate treatment in an intensive care unit. Assisted respiration, whether through intubation or mechanical ventilation, can help with breathing and ward off pulmonary edema. Intubation involves placing a breathing tube through your nose, mouth or trachea to help keep your airways open and functioning.
In extremely severe cases of pulmonary distress, you’ll need a method called extracorporeal membrane oxygenation to help ensure you retain a sufficient supply of oxygen. This involves continuously pumping your blood through a machine that removes carbon dioxide and adds oxygen. The oxygenated blood is then returned to your body.