Hantavirus is a rare but potentially deadly virus that is transmitted to humans by rodents, particularly deer mice. The disease caused by hantavirus infection is called hantavirus pulmonary syndrome (HPS) and has a mortality rate of 38-50% in the United States according to the CDC. While rare, hantavirus deserves attention because of this high fatality rate. Understanding the prevalence and transmission of this virus can help public health officials and individuals take appropriate precautions.
What is hantavirus and how is it transmitted?
Hantaviruses belong to the Bunyaviridae family of viruses. They are enveloped, negative-sense RNA viruses. There are several types of hantaviruses, such as Sin Nombre virus in North America and Puumala virus in Europe.
Hantaviruses are found in rodents, particularly deer mice in North America. The virus is shed in rodent urine, droppings, and saliva. Humans can become infected by breathing in virus particles that have been stirred up from rodent nests or droppings. Transmission can also occur by touching the mouth or nose after touching something contaminated with rodent droppings, urine, or saliva.
Rare cases of human-to-human transmission have been reported, but this is not thought to be a common route of infection. The time between hantavirus exposure and onset of symptoms is typically 2-3 weeks but can range from 1-6 weeks.
Symptoms of hantavirus
The disease caused by hantavirus infection in humans is called hantavirus pulmonary syndrome (HPS). It begins with non-specific flu-like symptoms including fever, muscle aches, headache, and gastrointestinal symptoms. After several days, respiratory distress and hypotension rapidly develop due to capillary leakage and fluid buildup in the lungs. This can quickly lead to respiratory failure.
The symptoms of HPS typically progress through three phases:
Prodromal phase
– Fever
– Fatigue
– Muscle aches
– Chills
– Headaches
– Nausea, vomiting, diarrhea
– Abdominal pain
Cardiopulmonary phase
– Shortness of breath
– Cough (initially dry cough, later productive of mucus)
– Low blood oxygen levels
– Fluid buildup in lungs
– Rapid heart rate
– Hypotension (low blood pressure)
Diuretic phase
– Improved lung function
– Increased urine output as fluid clears from lungs
– Low blood pressure remains
– Possible hospital discharge
The cardiopulmonary phase occurs about 2-10 days after initial symptoms and is when the high mortality rate is seen due to acute respiratory distress and cardiovascular collapse. Patients who survive this critical phase can enter the diuretic phase with improvement in symptoms. However, a long recovery is still needed. Mortality in HPS is around 38-50% in the United States.
Prevalence of hantavirus in humans
Hantavirus infection and HPS are rare in humans despite rodents being frequent carriers of the virus. According to the Centers for Disease Control and Prevention (CDC), there are an average of 17 HPS cases per year in the United States.1 However, this number likely underestimates the true incidence as hantavirus infections can be asymptomatic or have mild flu-like symptoms that escape diagnosis.
HPS cases occur throughout the year, but the majority are reported in the spring and summer when outdoor activities increase the risk of rodent exposure. HPS outbreaks have also been linked to increased rodent populations and weather conditions favorable to viral transmission.2
Cases by state
While cases have been reported in most states, HPS incidence varies geographically with the highest rates in rural areas of western states. As of December 2022, the states with the highest number of HPS cases since 1993 are: 3
| State | Number of HPS cases |
|---|---|
| New Mexico | 143 |
| Colorado | 122 |
| California | 94 |
| Arizona | 72 |
| Washington | 65 |
| Utah | 59 |
The higher incidence in western states is likely due to factors favoring rodent reservoir populations and viral transmission such as climate, vegetation, and human encroachment on rodent habitats. Proximity to rodents increases risk of hantavirus exposure.
Age and sex distribution
HPS can occur at any age but the highest incidence is in adults aged 30-50 years. Approximately 95% of cases are in individuals aged 14 and older.1
Males account for approximately two-thirds of HPS cases. The higher incidence in males is likely due to increased occupational and recreational exposure to rodent habitats. Activities like farming, ranching, camping, and hunting can bring humans into closer contact with rodents carrying hantaviruses.4
Case fatality rate
Despite advances in medical care, the case fatality rate for HPS remains high. Overall in the United States, the HPS case fatality rate is 38%. However, mortality varies depending on the viral strain causing infection. The Sin Nombre virus, common in North America, has a fatality rate around 35% compared to a 50% fatality rate for the Andes virus found in South America.1
Younger patients tend to have better outcomes than older patients. The HPS case fatality rate also varies based on access and timeliness of medical care. Patients who rapidly progress to respiratory failure and shock have a poor prognosis despite intensive care. There are no FDA-approved drugs or vaccines specific for hantavirus infection, so treatment relies on general supportive care.
Risk factors for hantavirus
The key risk factor for hantavirus infection is exposure to infected rodents or their droppings/urine in contaminated spaces. Activities or occupations involving rodent contact or disturbance of rodent habitats increase risk, including:
– Working in agriculture, ranching, forestry
– Camping or hiking, especially sleeping on bare ground
– Occupying rodent-infested buildings
– Working in laboratories that handle infected rodents
– Living in rural homes with nearby rodent habitats
Rodent infestations in and around the home greatly increase risk of hantavirus exposure and are linked to the majority of HPS cases. Rodent nests and droppings accumulate when buildings are not properly sealed. Activities like cleaning garages, cabins, and hunting shelters can stir up hantavirus particles.
HPS outbreaks have also been associated with weather patterns leading to increased rodent populations. For example, higher summer rainfall favors vegetation growth and boosts rodent food supply, allowing rapid reproduction. Mild winters also enable rodents to survive and breed.
Diagnosis of hantavirus
Diagnosing hantavirus infection can be challenging because early symptoms are similar to other respiratory infections and HPS mimics other causes of acute respiratory distress. However, hantavirus should be suspected if an individual with potential rodent exposure develops severe respiratory illness.
Tests available to aid diagnosis include:
– **Serology blood tests** – Detects antibodies to hantaviruses which appear shortly after symptom onset. A four-fold rise in antibody levels between acute and convalescent samples helps confirm recent infection.
– **RT-PCR** – Detects viral RNA in blood during the initial acute phase of infection. Samples should be collected promptly as viremia decreases shortly after symptom onset.
– **Immunohistochemistry** – Detects hantavirus antigens in lung biopsy or autopsy tissues. Can provide retrospective diagnosis via lung samples if HPS patient dies.
– **Viral culture** – Isolates infectious hantavirus by inoculating blood or tissue samples into cell culture. Requires Biosafety Level 4 containment so limited availability.
A presumptive diagnosis of HPS can be made clinically for patients with consistent symptoms and history of potential rodent exposure in known endemic regions. However, diagnostic testing is important to differentiate hantavirus from illnesses like influenza or COVID-19.
Treatment of hantavirus infection
There are no antiviral drugs or vaccines approved specifically for treating hantavirus infections. Management of HPS revolves around careful supportive care and treatment of symptoms:
– **Respiratory support** – Supplemental oxygen, mechanical ventilation, or ECMO may be required depending on severity of lung involvement.
– **Fluid management** – Cautious IV fluids to maintain organ perfusion without exacerbating pulmonary edema. Vasopressors may be needed for hypotension.
– **Renal support** – Dialysis if acute kidney injury develops.
– **Prevention and treatment of secondary infections** – Broad spectrum antibiotics, antivirals, antifungals.
– **Pain control** – Adequate analgesia for headaches, myalgia.
– **Patient monitoring** – Close observation for shock and respiratory failure which require aggressive interventions.
Experimental antiviral drugs like ribavirin have been attempted but none have established clear efficacy. Care is focused on managing complications and supporting vital functions to give patients the best chance of recovery. With supportive care, the mortality rate may be reduced to 12-15%.
Prevention of hantavirus
Preventing hantavirus exposure is the key to avoiding infection:
– **Control rodent populations** – Eliminate food sources, seal entry holes in homes and sheds, clean up clutter. Traps and rodenticides can also be used but avoid actions that stir up dust like sweeping dry rodent droppings.
– **Avoid rodent habitats** – Limit time in enclosed areas like barns and cabins with signs of rodents. Do not disturb nests or droppings. Open shelters and air out before cleaning.
– **Protective equipment** – Wear gloves, masks, and goggles if cleaning areas with rodent infestation. Dampen droppings before removal to limit dust. Disinfect contaminated surfaces with bleach solution.
– **Camping precautions** – Avoid camping near rodent burrows or droppings. Do not sleep on bare ground. Store food in sealed containers.
– **Screen windows and doors** – Ensure homes have tight-fitting screens on windows and doors to prevent rodent entry.
– **Vaccinate pets** – Dogs and cats can bring infected rodents into homes. Keep pets up-to-date on vaccinations which may offer protection against diseases like hantavirus.
Awareness and vigilance are key to averting hantavirus infection. Rodent control measures and avoiding contact with rodents or disturbed nests/droppings can significantly lower risk. Seek medical care promptly for fever or respiratory symptoms after potential rodent exposure.
Conclusion
In summary, hantavirus infection is uncommon in humans but can cause a life-threatening disease called HPS. Transmission occurs by inhaling aerosolized virus from the droppings, urine, or saliva of infected rodents. HPS has a high mortality rate around 36-50% in the United States. Hantavirus cases concentrate in western states where ecology favors rodent reservoir populations. At-risk individuals include those with occupational or recreational exposure to rodents. Preventive measures focus on controlling rodents, avoiding their habitats, and using protective equipment when cleaning areas with rodent infestation. There are no specific treatments for hantavirus infection, so patient management relies on careful supportive care. With appropriate precautions and prompt medical attention, the otherwise deadly threat of hantavirus can be contained.