Health protection – guidance

Hantaviruses

The characteristics, diagnosis, epidemiology of hantaviruses.

Hantaviruses, from the Bunyaviridae family, are a group of viruses that are normally carried by rodents, such as rats, mice and voles. They are present throughout the world and they cause a range of diseases in humans ranging from mild, flu-like illness to severe respiratory illness or haemorrhagic disease with kidney involvement.

Old World hantaviruses (those present in Europe, Asia and Africa) tend to cause haemorrhagic and kidney disease, whilst new world hantaviruses tend to cause severe respiratory disease.

Hantaviruses causes 2 serious infections in humans:

  • haemorrhagic fever with renal syndrome (HFRS)
  • hantavirus pulmonary syndrome (HPS)

Transmission

Each hantavirus is specific to a different rodent host. Once infected the rodent will secrete infectious virus for prolonged periods, probably for life. Transmission of the virus to human occurs through the inhalation of infected animal excreta and fluids, such as urine, faeces and saliva

To help reduce the risk of infection, simple hygiene precautions such as washing your hands after handling rats or their bedding and cage should be applied.

Haemorrhagic fever with renal syndrome (HFRS)

HFRS is a group of clinically similar illnesses occurring worldwide, and including Korean haemorrhagic fever, epidemic haemorrhagic fever, and nephropathia epidemica. The viruses that cause HFRS include Hantaan, Dobrava, Seoul, and Puumala.

The incubation period is generally 2 to 4 weeks but can range from 2 days to 8 weeks.

Infection with these viruses can cause a disease characterised by fever, headache, gastrointestinal symptoms and renal dysfunction. The more severe forms of disease have haemorrhagic (bleeding) manifestations. Dobrova and Hantaan viruses cause a more severe HFRS with fever, haemorrhage, and renal failure, and a mortality rate of up to 15%. Seoul virus causes a moderately severe disease resembling that due to Hantaan virus.

Nephropathia epidemica is the mildest form of HFRS, and is caused by Puumala virus, the most common hantavirus, present in most countries in north-western Europe. Nephropathia epidemica has an abrupt onset with fever and myalgias, thrombocytopaenia (low blood platelet count) and sometimes myopia. An acute renal failure occasionally requiring dialysis can occur.The mortality rate is < 0.1%.

Epidemiology of HFRS

Haantan virus is widely distributed in eastern Asia, particularly in China, Russia, and Korea. Puumala virus is found in Scandinavia, western Europe, and Russia. Dobrava virus is found primarily in the Balkans, and Seoul virus is found worldwide. Saaremaa virus also circulates in northwest Europe.

About 150,000 cases of HFRS are thought to occur annually worldwide. Very few cases of hantavirus infection have been confirmed in the United Kingdom, although there are seroprevalence data to suggest that exposure does occur.

The first case of Seoul hantavirus infection in the UK was confirmed in 2012, with virus being isolated from wild rats at the location of exposure.

Hantavirus pulmonary syndrome (HPS)

Sin Nombre virus, the common cause of HPS in the USA, was discovered in 1993 following a cluster of acute and fatal illness in previously healthy adults. The cluster occurred in an area of the southwestern USA known as ‘Four Corners’. It was later established that the virus had caused human disease at least as early as 1959, and that the disease syndrome was well-recognised among the Navajo indians in whom it was observed. By the end of 2012, a total of 617 cases of HPS had been reported in the United States. Thirty-five percent of all reported cases were fatal.

HPS is more common in South America than in North America. Cases have been identified in Argentina, Bolivia, Brazil, Chile, Ecuador, Paraguay, Panama and Uruguay and Venezuela.

Andes virus causes HPS in Argentina and Chile, and is the only hantavirus known to have been transmitted from person to person. Large outbreaks have been rare and have usually been associated with human disturbance and land-use changes or with unusual environmental events such as increased rainfall.

Diagnosis

Rare and imported pathogens laboratory (RIPL) is a specialist centre for advice and diagnosis for a wide range of unusual viral and bacterial infections including hantaviruses.

Epidemiology

Each hantavirus is specific to a different rodent host, and the epidemiology of each virus is therefore closely linked to the ecology of its host. Once infected the rodent will secrete infectious virus for prolonged periods, probably for life. Transmission of virus between rodents and to humans occurs through inhalation of infected animal excreta and fluids, such as urine, faeces and saliva.

Bites may also be a factor in rodent infections, and have occasionally been reported for human infections. Occupational risk factors are important for infection: trapping, forestry workers, farmers, and military personnel are amongst those in whom infection occurs. Exposure to rodent excreta via working with wood piles and entering/cleaning long abandoned buildings are also associated with a risk for hantavirus infection.

The possibility of exposure amongst campers, hikers and tourists to endemic areas is generally considered to be low, and can be reduced if rodent contact is avoided.

Virus Disease Rodent host Distribution
Puumala HFRS Bank vole (Clethrionomys glareolus) Europe
Dobrava HFRS Yellow-necked field mouse (Apodemus flavicollis) The Balkans
Hantaan HFRS Field mouse (Apodemus agrarius) Asia
Seoul HFRS Rats (Rattus rattus, Rattus norvegicus) SE Asia, worldwide (including the UK)
Sin Nombre HPS Deer mouse (Peromyscus maniculatus) North America
Andes HPS Long-tail pygmy rice rat (Oligoryzomys longicaudatus) Argentina

Spring and summer rises in cases in Asia are related to increased rodent contact during seasonal planting and harvesting activities. Puumala virus infection in western Europe tend to occur between March and November, with peaks in August and September.

The bank vole, host to Puumala virus, is a small mammal that eats seeds, fruits of trees and bushes, and green plants. The population dynamics of these animals are directly influenced by the seed production of trees, especially oak, beech and acorn. Years with increased seed production (called ‘mast’ years), mediated by favourable climatic conditions (including mild winters and dry summers), give rise to increased rodent population densities in the following year.

Clinical study

Public Health England (PHE) has designed and carried out a clinical study to investigate the incidence of hantavirus infections in identified risk groups. The study will determine previous exposure to hantaviruses through the detection of antibodies against these viruses in 3 ‘at risk’ groups (pet rat owners, those who work with pet rats and those with occupational exposure to wild rats (farmers, pest control workers, waste water workers)) compared to a baseline taken from the general population.

We are currently seeking volunteers from people who breed pet rats for the commercial pet industry and from people who own pet rats bought from a commercial vendor (eg a pet shop) to assess the risk of exposure to hantaviruses in these groups.

You can volunteer for this study, which will involve either your local GP or a trained nurse taking a small blood sample (10ml), and filling in a questionnaire related to the study. If you are interested in our study and would like to volunteer, or if you have any questions about the study, please send an email to hantavirus_study@phe.gov.uk.

Read the preliminary results from the Hantavirus infection in people: sero-surveillance study in England.