Hantavirus Pulmonary Syndrome
What is Hantavirus pulmonary syndrome?
Hantavirus pulmonary syndrome is an infectious lung disease caused by Hantavirus. This virus is very rare but its manifestation can be deadly. It can present with flu like symptoms but quickly progress in life threatening lung disability.[1]
How do you get Hantavirus?
Hantavirus belongs to a virus group called zoonotic viruses. That means that they are transmitted to humans from animals. In case of Hantavirus, it is transmitted to humans form rodents. There are many types of this virus, that all can cause Hantavirus pulmonary syndrome. Different types of virus are carried by different rodent species. It is possible to get infected by:
- Breathing in the virus particles from the air, that have come from rodent urine
- Touching mouth, eyes or nose after touching saliva, urine, droppings of rodents or their nests containing the virus
- Breathing in dust that has virus contamination
- Being bitten by a rodent carrying the virus
Everyone who is in contact with rodents that are possibly infected is at risk. This virus can even be lethal for healthy individuals. [2] [3]
Hantavirus Incubation Period and Description
The structure of Hantavirus
Image source:nature.com
Hantavirus is a sphere-shaped RNA virus, around 80nm big in diameter. It has a lipid envelope that contains 2 glycoproteins that are responsible for the virus binding with cells in human body. The virus binds to host cells and then releases its genetic material in human cells. There virus continues to reproduce, and spread in the body. There are different types of this virus but they all have similar effects. Hantavirus pulmonary syndrome first occurred in United States in 1993. The syndrome was characterized with a beginning of flu-like symptoms and following acute respiratory distress syndrome and death. [4]
The incubation period for this virus is 1-4 weeks.[5]
Symptoms
There are 3 stages of this disease- prodrome, cardiopulmonary phase and convalescence.
HPS usually starts with unspecific symptoms that can lead up to 5 days. These symptoms can vary in their severity but mostly they progress:
- Fever and chills, sweating
- Muscle pain (myalgia)
- Headache
- Abdominal pain, nausea and vomiting
- Cough
- Diarrhea
In rare cases this phase can also present with joint pain (arthralgia), chest pain shortness of breath and dizziness.
The disease moves to the next phase. In the prodrome period diagnosis is seldom made, because the symptoms are very unspecific. The symptoms rapidly get worse. Mostly patient’s condition gets life threatening after first 24 hours in the hospital. Blood pressure get low, while heart rate rises. Patient has trouble breathing and there are signs of lung edema and effusion.
Oxygen saturation can get critically low, and patient is hypoxic. Usually mechanical ventilation is required. In severe cases patient might present with acute coronary syndrome. In HPS multiorgan failure syndrome is rarely seen, but there might be impaired kidney function. Kidney function usually gets better in reconvelescance period, but patient might present with Overactive bladder syndrome for some while.
Pathophysiology
Once the virus has binded with human cells and started to reproduce, the body react to the foreigh substance by sending antibodies to fight the viral antigens. That causes damage in the walls of small blood vessels- capillaries, and they become permeable. The symptoms start to appear when the body produces the specific antibodies. Because the capillaries become permeable, fluid rich in proteins spreads to surrounding tissue.
In case of HPS, the edema is usually located in pleura and lungs, causing the severe symptoms, even acute respiratory distress syndrome. Hypotention occurs due to lack of volume in blood vessels. The state of shock occurs due to hypoxia and lack of circulating blood.
How is Hantavirus diagnosed?
Hantavirus Pulmonary syndrome rarely gets diagnosed in the initial stage of flu-like symptoms, because they are not specific. A red flag for Hantavirus should be if the patient has known history of being in contact with rodents. For example, the patient lives in a farm, has just done construction work in an abandoned building.
The next step is to do physical examination and exclude other possible diseases, like influenza. If Hantavirus infection is suspected, further laboratory investigations have to be done in order to prove the presence of the virus.
Hantavirus diagnostic tests
- Serologic tests – by using serologic analysis the viral antigens or viral RNA traces can be found
- It is possible to isolate the virus from animals, but for humans this method is not applicable
- Immunohistochemistry– uses tissues that are fixed with formalin and marked with specific antibodies, that connect to Hantavirus antigens, therefore making these conglomerates visible and proving the presence of Hantavirus
- Polimerase chain reaction assay can be used to find Hantavirus RNA in tissue samples. This diagnostic test is still experimental for detecting this virus.
Immunohistochemistry of tissue simple. The red dots are antigen-antibody conglomerates.
Image source: cdc.govt
Imaging studies
To help the diagnosis of HPS X-ray imaging is usually done. In X-rays usually lung edema can be seen. The changes vary from interstitial edema on one side and rapidly progress to alveolar edema in both lungs.
Progression of pulmonary edema
Image source: cdc.gov
How common is Hantavirus?
In United States there have been a total of 690 reported cases since 1993. From those patients 63% were male and 37% were female. Mortality rate from this virus is 30%.
Differential Diagnosis
The initial phase of HPS is similar to a range of viral infections, but the rapid progression of severe symptoms is similar to following diseases:
- Leptospirosis
- Tularemia
- Hystoplasmosis
- Septicemic plague
- Q fever
From non infectious diseases, Goodpasture’s syndrome should be considered. Symptoms of HPS are also similar to the range of Gulf War syndrome symptoms.
For immunocompromised patients the following should be considered:
- Cytomegalovirus
- Cryptococcus infection
- Aspergillus infection
- Graft vs host disease
Treatment of Hantavirus
There is no specific treatment for Hantavirus pulmonary syndrome. The treatment used is mostly symptomatic. If the diagnosis is unclear, but the symptoms get worse, patients should undergo antibiotic treatment until the cause of the condition has been found. Other measures that can be taken are:
- Medication to lower the fewer and pain
- When the condition gets worse, patients have to be taken to intensive care unit
- Oxygen supplementation or mechanical ventilation if the oxygenation is compromised
- If cardiac function deteriorates, inotropic and vasopressive medications can be used
- http://emedicine.medscape.com/article/236425-overview#a5
- https://www.cdc.gov/hantavirus/pdf/hps-fact-sheet.pdf
- http://www.cdc.gov/hantavirus/index.html
- http://viralzone.expasy.org/all_by_species/213.html
- http://emedicine.medscape.com/article/236425-clinical
