FAQs for Hantavirus infections
Definitions: see either → mouse over or, for prints at the end
Most Hantaviruses propagate in rodents, such as rats, voles and mice, without causing any obvious symptoms (though having some hidden impact); others were detected in insectivores like shrews and moles, and also in bats (without known pathogenicity to humans, and no item here). The viruses can be transmitted (passed on) to humans by inhalation of aerosolized urine, feces, or saliva from the rodents. Many different kinds of Hantaviruses have been discovered so far. Usually, each one is found in a specific host species, or sometimes in a group of closely related host species. The geographic distribution of a Hantavirus depends on the distribution of the host species. The virus known as the Hantaan virus is carried by the striped field mouse (Apodemus agrarius). It is found in Korea, China, and East Siberia. In North, East, and Central Europe, and the Balkans the Dobrava–Belgrade virus (DOBV) is transmitted by other Apodemus species.
Hantavirus in Europe: The most common Hantaviruses in Europe cause → Hemorrhagic Fever with → Renal Syndrome (HFRS). Of the two hantaviral diseases, HFRS and hantaviral → cardiopulmonary syndrome (HCPS), the European and other Old World viruses only cause HFRS: DOBV-DOBV with often severe symptoms and a high case fatality rate (CFR), and Puumala virus (PUUV) and DOBV-Kurkino Virus more often cause disease with a mild course. More than 10,000 HFRS cases are diagnosed in Europe annually, with numbers increasing. Whether this is because of increasing recognition by the medical community or because of environmental factors such as climate change, or both, is not known. Nevertheless, in large areas of Europe, the human population has a considerable →seroprevalence but only relatively few HFRS cases are reported, suggesting heavy underdiagnosis in regions where the disease is poorly known. From many countries no epidemiological data are available. On the other hand, several countries are known for being → endemic e.g. in parts of Germany, Belgium or the whole Finland, the last one with the highest → incidence of HFRS due to Puumala Hantavirus in the EU (ca. 30,000 cases and max. 20 deaths have been recorded in Finland since 1995).In addition to → renal changes, we know now that cardiac, → pulmonary, ocular and hormonal disorders are common during the acute stage of PUUV and DOBV infection. About 5% of hospitalized PUUV and 16%–48% of DOBV patients require dialysis and some prolonged intensive care treatment. Although PUUV–HFRS has a low case fatality rate (in Europe < 1%), complications and long-term hormonal, → renal, and → cardiovascular consequences occur frequently.
Hantavirus in the Americas: Another type of Hantavirus is called Sin Nombre virus. It is carried by the deer mouse (Peromyscus maniculatus), was first detected in the South-West of the United States (now known to occur also in other parts of the US and Canada), and brings on severe cases of HCPS which cause the lungs to fill with fluid and can introduce respiratory failure. There are quite a number of these New World Hantaviruses. However, in spite of different names for the diseases, the division of symptoms between these virus groups is not clear-cut.
For providing helpful information regarding Hantavirus infections we selected seventeen frequently asked questions raised by public health experts and the public and answer them according to current knowledge and information available.
- How can it affect you? How do you acquire the disease
The viruses can be transmitted (passed on) to humans by inhalation of aerosolized urine, feces, or saliva from the rodents. Hantaviruses differ in their virulence to humans. Hantaviruses that are spread by Old World rats and mice are less virulent, CFR being between 2–12%, depending on the specific virus. Those spread by voles have a CFR lower than 1%, and some Hantaviruses spread by voles seem to be almost nonpathogenic. The most common Hantavirus in Europe is Puumala virus, and it is known that only about 20–25% of persons with antibodies, marking past infection, have had an acute disease. So, maybe 75% of the infections do not lead to an acute diagnosed disease. Still, all infections result in permanent life-long immunity.
The CFR by some New World Hantaviruses is high, around 40%, but cases are rare.
- How are the symptoms in case I caught the disease?
The two forms of Hantavirus infections each have distinctive symptoms.
The three most common symptoms of Hemorrhagic Fever with Renal Syndrome (HFRS) in the Old World are mentioned in the name of the disease. The first of those symptoms is high fever over several days, combined with headache and strong back pain. The second, more severe symptom is malfunction of the kidneys found in several patients. The term renal means "relating to the kidneys." The third symptom is a low platelet count. Platelets are blood cells that promote the clotting of blood. When the number of platelets in blood is reduced, blood clotting does not occur properly. A person tends to hemorrhage or bleed easily. However, most cases of infection occur in a very mild form, patients are not aware of a Hantavirus infection, but show flu-like symptoms for a few days. But blood tests show evidence of a previous infection (àseroprevalence).
The incubation time for HFRS is at least 2 weeks, often 3 weeks, and can be up to 6 weeks. Patients with HFRS have a headache, stomach ache, and lower back pain. They may also have bloodshot eyes and blurry vision. Hemorrhaging may occur through tiny openings on the upper body and in the mouth. The patient’s face, chest, abdomen, and back often appear bright red, as if sunburned. The severity of disease and symptoms vary due to different viruses like PUUV and DOBV-Dobv.
Five days into the disease, the patient may experience a sudden drop in blood pressure. He or she may go into shock. Shock occurs when the heart fails to pump enough blood through the veins and arteries. Cells are not provided with blood and the needed oxygen it carries. Shock can cause damage to the body’s organs, especially the brain.
After about 8 days without proper treatment or committed to hospital, kidney damage may have taken place. The kidneys are responsible for filtering toxins (poisons) out of the blood. If the kidneys do not function properly, these toxins can damage cells throughout the body. Hemorrhaging may also become more severe throughout the body. Blood may begin to appear in the urine or when a person vomits. Hemorrhaging in the brain can cause the most serious problems including loss of consciousness.
These symptoms can become even more severe about eleven days into the infection. A person may become very confused, begin to hallucinate, and go into seizures. A person who hallucinates sees and hears things that are not really there. Problems can also develop with the lungs and the ability to breathe normally.
At this point, the patient faces a turning point. He or she may continue to become more and more ill, resulting in death (which has been seen in very few cases). Or the infection may begin to clear up. In the latter case, full recovery may take up to six weeks. After overcoming a Hantavirus infection, the person is resistant from acquiring the same Hantavirus infection in life span.
There is no way to kill the Hantavirus. Antibiotics do not work against viruses. Treatments for Hantavirus infections are designed, therefore, to relieve the symptoms of the disease. For example, a person who has been hemorrhaging or who is inà shock may require blood transfusions.
à Hemodialysis is used to remove toxins from the blood of a person whose kidneys have failed (around 5% in PUUV cases).
Severe/fatal Hantavirus infections progress very rapidly once the clinical symptoms appear. Therefore it is important to begin treatment as soon as possible and to observe the patient very carefully.
The first symptoms of Hantavirus → Cardio Pulmonary Syndrome (HCPS) are fever (38–40°C/101–104°F) and a sudden drop in blood pressure. These symptoms may be followed byàshock and loss of blood in the lungs. When this happens, fluids may collect in the lungs, leading to shortness of breath. These symptoms can occur so quickly that the patient goes into respiratory failure in a matter of hours. Respiratory failure means that the patient has lost the ability to breathe on his or her own.
If persons get HCPS, they will feel sick for 1 to 2 weeks (rarely up to 6 weeks) after they had been around mice or rats that carried Hantavirus. At first persons with HCPS will have fever, severe muscle aches and/or fatigue.
After a few days they will have hard time breathing. Sometimes persons will have headaches, dizziness, chills, nausea, vomiting, diarrhea, and stomach pain. Usually, they will not have a runny nose, sore throat, or a rash.
In Europe, the most common Hantavirus Puumala causes a CFR of less than 1%. Asian Hantaan virus causes HFRS with CFS of 2–6 %. Global Seoul Hantavirus spread by Norway rats has a CFR of 1–2%. The Hantavirus in the Old World with the most severe course is the Dobrava strain. In Southeast Europe, Dobrava has a CFR of 10%, but fortunately human cases are rare. The CFR of those who contract HCPS in the Americas is about 30–40%. These numbers point out how important it is for persons with symptoms of a Hantavirus infection to get treatment as quickly as possible.
An experimental drug being tested on Hantavirus infections is called →Ribavirin. The drug has been shown to kill the Hantavirus in laboratory tests. Treatment must be started early in the course of the disease.
- How will a Hantavirus infection be diagnosed?
Based on the clinical diagnostics analyzing the patient’s symptoms, blood tests are used to diagnose Hantavirus infections. Blood taken from a patient is analyzed for the presence of specific Hantavirus antibodies. Antibodies are substances produced by the blood when it has been infected by a foreign body, such as a bacterium or a virus. Antibodies are very specific. An analysis of a person’s blood can tell whether he or she has been infected with a Hantavirus and, if so, sometimes by what kind of Hantavirus. Blood tests can also tell whether it is a fresh infection (acute disease) or if the person has had the infection earlier. Antibodies directed against Hantavirus remain and protect for the rest of life.
- Which age groups are at higher risk (in particular older persons or children)? Is everyone at the same risk of catching the disease?
Anyone, young or old, male or female, any race, living almost anywhere can be exposed to the Hantaviruses. Anything that puts you in contact with rodent droppings, urine, or nesting materials poses a risk of Hantavirus infection. Dusty work inside seems to be a risk factor. A single most important risk factor is smoking. Because the infection is mostly acquired through inhalation, obviously the villi in the lungs of smokers do not function properly and do not remove the contaminated dust particles.
- Are there are specific groups that are more vulnerable to the disease than others?
There are some groups with a higher risk of infection like forest workers, farmers, and persons entering lofts or basements or cleaning garden huts or sheds, places where rodents might be.
Anyone who comes into contact with rodents that carry Hantavirus is at risk of HFRS or HCPS depending on the geographic area. Rodent infestation in and around the home and working place remains the primary risk for Hantavirus exposure.
Travelers should be advised to avoid exposure to rodents and their excrements. Adventure travelers, backpackers, campers, joggers and workers with occupational exposure to rodents in countries or areas at risk for Hantaviruses should take precautions to banish rodents from tents or other accommodation and to protect all food from contamination by rodents.
Opening or cleaning cabins, sheds, and outbuildings, including barns, garages, and storage facilities that have been closed during the winter is an activity with a potential risk of Hantavirus infection, especially in rural settings.
Cleaning in and around your own home can put you at risk if rodents have made it their home, too. Many homes can be expected to shelter rodents, especially as the weather turns cold. Construction, utility, and pest control workers can be exposed when they work in crawl spaces, under houses, or in vacant buildings that may have a rodent population.
Campers and hikers can also be exposed when they use infested trail shelters or when camping in rodent habitats.
The chance of being exposed to Hantavirus is greatest when people work, play, or live in closed spaces where rodents are actively living. Recent research results show that many people who have become ill with Hanta were infected with the disease after continued contact with rodents and/or their droppings. However, many people who have contracted Hanta reported that they had not seen rodents or their droppings before becoming ill. Therefore, if you live in an area where the carrier rodents, such as the bank voles in Europe or deer mouse in America, are known to live, take sensible precautions-even if you do not see rodents or their droppings.
- What are determinants for disease development?
In the case of Puumala virus in Europe about 75% of the infections do not lead to acute disease; still these people will get life-long immunity without knowing it. Among the 20-25% developing an acute disease, the course can vary from mild to severe, even fatal in rare occasions. There is → immunogenic background for a severe disease, i.e. if you get the disease, with a specific genetic background it will probably be severe. Depending on the specific virus and geographic region around the world, the CFR varies a lot. In Europe, a mild form of HFRS (called nephropathia epidemica) caused by Puumala Hantavirus has a CFR lower than 1%, while in North America HCPS due to Sin Nombre Virus has a CFR of 30–40%. If the infection leads to a clinical disease, the disease the course could range from rather mild and unapparent to severe requiring intensive care. The course of the disease depends on different parameters including personal conditions and → immunogenics , the type of Hantavirus, and the route and dose of infection.
- What is the treatment for Hantavirus infection?
There is no specific treatment for Hantavirus infection and there is no way to kill the Hantavirus. No antibiotics to viruses. Treatments for Hantavirus infections are designed, therefore, to relieve the symptoms of the disease. For example, a person who has been hemorrhaging or who is in shock may require blood transfusions. → Hemodialysis is used to remove toxins from the blood of a person whose kidneys have failed, around 5% in PUUV cases.
Severe Hantavirus infections progress very rapidly. Therefore it is important to begin treatment as quickly as possible and to observe the patient very carefully.
If the symptoms are severe and recognized early, the patient should be taken to an intensive care unit. The earlier the patient is brought into intensive care, the better. In intensive care, patients are intubated and given oxygen to help them through the period of severe respiratory distress. Therapy for HFRS is supportive and symptomatic. The water balance is checked in cases of kidney failure. If there is no decrease in retention a temporary hemodialysis is recommended. In severe HFRS, → shock is not uncommon, and the medical personnel should be careful not to run the usual shock therapy because the kidneys of the patient are probably nonfunctional by then.
Intravenous ribavirin, a guanosine analogue, has not been shown to be effective for treatment of HCPS despite its positive effects on HFRS, which is caused by Old World Hantaviruses. Controlled trials showed a reduction in CFR for HFRS patients treated with ribavirin when treatment has been started early enough.
- When do I really need to take protective measures?
In some cases, people who are at occupational risk, such as farmers, wood loggers or rangers in → endemic areas, or those who camp in endemic areas, might be advised to take protective measures for specific activities (such as brushing sheds or loading wood), including the usage of protective breathing masks and wearing gloves. However, the US Centers for Disease Control and Prevention (CDC) does not recommend routine use of protective masks by farmers and homeowners in rural areas. CDC guidelines (MMWR 1993; 42, RR-11) address specific risk-reduction measures for rural residents (rodent proofing, environmental management, and trapping) and precautions to be taken during activities that may pose an increased risk of Hantavirus infection (cleanup of rodent-infested areas). Cleanup of heavy rodent infestations or of homes associated with known cases of Hanta are special instances for which we do recommend respiratory protection, but these tasks are best left to pest control or public health professionals. There is no evidence that farmers operating farm machinery in open fields (even though rodents may be crushed in the machinery) are at increased risk. Nevertheless farming and forestry work is a risk factor for contracting the disease. Under these conditions, the natural circulation of air and → virucidal properties of natural UV light and high temperatures make inhalation of infectious aerosols less likely. At room temperature Puumala Hantavirus remains infectious for 2 weeks and at low temperatures in winter clearly longer. However, if a person has some permanent health problems (heart, high blood pressure, kidney problems, or cancer therapy), he or she may use single use face masks when e.g. carrying fire wood from wood sheds or doing wood related work.
- How far away from bank voles’ living environment is far enough to prevent human infection?
It is not possible to indicate in detail how far away from bank voles living environment is far enough not to catch the disease as there is no knowledge available on this. However, in autumn with declining temperatures bank voles tend to invade human dwellings and sheds from their forest habitats. What we know however, is that the possibility of human exposure is greater in indoor closed spaces, such as barns, attics and sheds that may be infested with rodents than outdoors. It is therefore important that outbuildings be rodent-proofed to the greatest extent possible. The thumb rule is that a bank vole can enter into the beer bottle; therefore the wire mesh size should be preferably less than 10 mm. When effective rodent proofing is not possible, snap traps (and, if necessary, rodenticides) should be used continuously, and recommended precautions (concerning airing out and cleanup of infestations) should be followed when entering such buildings after periods of non-use.
- Is the virus really everywhere? Can you avoid exposure?
No, Hantaviruses are not everywhere in the world. You may learn more about the occurrence when looking to the recorded human cases. In regions where Hantaviruses are known (→ endemic areas) they really might be almost everywhere. It is not necessary when seeing a rodent to assume automatically that there are Hantaviruses around. The most problematic scenario is the presence of rodent droppings in closed rooms – however, avoidance of exposure is possible: If you are at risk of exposure, because of your profession or living place, you may use an FFP3 mask. For cleaning rooms it is important to use gloves.
- How to prevent the risk? Which kind of specific measures could be applied to prevent infection?
The best way to avoid getting the disease is to reduce one’s exposure to the rodents that carry the virus. That means keeping one’s living quarters as clean as possible.
Recommendations for outdoor activities.
Avoid touching live rodents or disturbing rodent burrows, dens, or nests.
Keep food in tightly sealed containers and store away from rodents.
Take care not to stir up dust.
- Minimize storage of luggage and other materials on the floor.
- Contact housekeeping or maintenance if signs of rodents are present, including feces or urine.
- Do not pitch tents or place sleeping bags in proximity to rodent feces or burrows or near possible rodent habitats (for example, dense brush or woodpiles).
- Use a tent with a floor. Avoid sleeping on bare ground.
- Use a cot with the sleeping surface at least 30 cm/12 inches above the ground.
- Dispose of all trash and garbage promptly in accordance with campground regulations by discarding in rodent-proof trash containers, or packing it outside in rodent-proof containers.
Recommendations for living at home:
Keep food in thick plastic or metal containers with tight lids.
Clean up spilled food right away. Wash dishes and cooking utensils soon after use.
- Put pet food away after use. Do not leave pet food or water bowls out overnight.
- Keep garbage in thick plastic or metal containers with tight lids.
- Check inside your house for gaps or holes that a pencil can fit into. Seal them with steel wool, lath metal, and caulk, wire mesh of 5–6 mm. Place wire mesh between the wall and roof so that rodents cannot enter the house by climbing the walls.
- Inside your home, use snap traps baited with apple, bread, or cheese.
- · Most important: Avoid smoking.
- Recommendations for outdoor activities.
- Is working with fire wood dangerous?
In a Hantavirus-endemic area any place in contact with rodent excrements might be pose a risk of getting infected if no precaution measures are taken. In Europe, bank voles often enter wood sheds in autumn and winter. It is better to cut the fire wood outside, not inside a dusty shed. Also, it is wise to keep mouse traps stocked continuously in the autumn and winter to remove invading rodents before they shed the virus. At room temperature Puumala Hantavirus remains infectious for 2 weeks and at low temperatures in winter clearly longer.
- How to distinguish a bank vole from other kinds of mice, and normal house mice, respectively? What does a bank vole or a deer mouse look like?
The morphological differentiation of a vole and a house mouse is quite easy – you only have to check the length of the tail. For voles the tail is much shorter than for the house mouse and other mouse species, like the yellow-necked mouse and the striped field mouse (in mice the tail is almost or as long as the whole body; in voles the tail is much shorter, only a short part of the body). The differentiation of a bank vole from other voles, like the common vole or field vole, is much more difficult.
The bank vole (Myodes glareolus; formerly Clethrionomys glareolus) is the natural reservoir of Puumala virus (PUUV) in Europe For comparison with the short tailed voles here the yellow-necked mouse (Apodemus flavicollis) with a long tail. The deer mouse (Peromyscus maniculatus) is the primary reservoir species for Sin Nombre Hantavirus in North America.
- Which factors influence the living conditions of bank voles?
The living conditions of bank voles are mainly driven by environmental factors (like climate, food resources (in temperate Europe by seed crop, years of beech and oak → mast, moisture), predators, etc.) as well as human behavior supporting the living conditions by “providing” dry places like barns, sheds, etc. and food in gardens and agriculture.
- What is determining where rodents feel at home and where do they move?
Each rodent species has habitat preferences. The bank vole is a forest and forest edge rodent, as the yellow-necked mouse and the wood mouse, whereas the common vole is found in an open grassland habitat and in agricultural settings. Commensal rodents, as the house mouse or the Norway rat, are following human settlements – they can be found in urban areas, but also in agricultural settings.
- Where are →endemic areas? What are exact risk areas – risk on a smaller scale? How do I know if the Hantavirus is currently an issue for camping, hiking, etc. in the area I live in?
Endemic areas are usually defined by notification of human Hantavirus cases. Some countries use this information to draw risk maps showing endemic areas.
In Europe the endemic areas expand from the Ardennes in France and Belgium through Central and Eastern Europe up to Finland and Sweden and Norway.
One prerequisite to defining risk areas is the occurrence of the Hantavirus reservoir host. However, the occurrence of the host is not sufficient for the virus actually being there. Thus, Puumala virus is not homogeneously distributed in the bank vole populations. Even in highly-endemic regions, there are vole populations where the virus is absent except for Finland and Northern Sweden where virus is found everywhere in the continuous boreal forests. The distribution of human Dobrava-Belgrade virus, strain Kurkino infections is more localized, most likely caused by focal occurrence of the virus in local striped field mouse populations.
- Is there a correlation between the weather conditions and the appearance of potentially infected bank voles?
There are seasonal and geographic differences in the→ incidence of notified Hantavirus cases. In northern Europe, the prevalence of Puumala virus in bank voles is seasonal. The proportion of infected voles increases through autumn and winter until spring. This happens also in low densities. However, the number of infectious voles is highest in early to mid-winter of cyclic peak years, when human infections also peak. In temperate Europe, →mast falls down in October, and therefore bank voles survive well, even breed in winter and certainly early in spring. Consequently, vole densities (also the density of infectious animals) are very high already in early summer, and in these post mast years human epidemics take place in early summer. Thus, there are clear geographic differences in the epidemiology of human cases, due to the geographic differences in vole dynamics. In some countries, there are also smaller epidemic peaks in August–September after summer holidays during which people have been exposed to rodent viruses.
- Explanations, references and pictures
Cardio: Relating to the heart Endemic: Disease or something that is native to or commonly found within an area Hemodialysis: A mechanical method for cleansing blood outside the body (replacing the function of the kidneys) Hemorrhagic: Relating to a condition in which there is massive, difficult-to-control bleeding Immunogenic: Relating to or producing an immune response Incidence: number of disease cases / 100 000 people Mast: The fruit of deciduous trees such as beech, oak etc. Platelets: Blood cells that have a role in the process of blood clotting Pulmonary: Relating to the lungs Renal: Relating to the kidneys Ribavirin: A nucleosid analogon that acts virostatic against a number of DNA- und RNA- viruses as e.g. Hepatitis-C virus, respiratory syncytial virus, Influenza viruses, Herpes viruses, Arenaviruses, Hantaviruses und Adenoviruses. It is used as a drug Seroprevalence: Proportion (%) of persons in a population who test positive for a specific disease Shock: A condition in which blood pressure drops suddenly and the flow of blood to cells is dramatically reduced. Because of this reduced flow, cells are not able to get the oxygen they need Vascular: Relating to, or involving the heart and blood vessels Virucidal: Having the capacity to or tending to destroy or inactivate viruses
Vaheri A. et al., Hantavirus infections in Europe and their impact on public health. Rev Med Virol. 2013 Jan;23(1):35-49. doi: 10.1002/rmv.1722. Epub 2012 Jul 3.
Vaheri, A., et al. 2013. Uncovering the mysteries of Hantavirus infections. – Nature Reviews in Microbiology 11:539-550. doi:10.1038/nrmicro3066.