Hantaviruses

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

People can become infected by exposure to infected rodent excreta (for example faeces or urine) in areas the virus is known to be present. One type of hantavirus (Andes virus) has shown potential to spread from person-to-person. Due to this, in the UK, Andes virus (ANDV) is classified as an airborne high consequence infectious disease (HCID). More information can be found at Andes hantavirus: epidemiology, outbreaks and guidance.

Hantaviruses can cause 2 major syndromes in humans:

• haemorrhagic fever with renal syndrome (HFRS), mainly restricted to Old World hantaviruses found in Europe and Asia, occasionally the Americas; the severity of the syndrome is variable depending on the causative virus, with case fatality rates from less than 1% to 15%
• hantavirus cardiopulmonary syndrome (HCPS), restricted to New World hantaviruses found in the Americas. HCPS is associated with a high case fatality rate of 30 to 50%

Hantaviruses are present in Africa but there is limited published evidence of human infections.

Epidemiology

Hantaviruses are uncommon infections globally, with between 10,000 to 100,000 cases occurring annually. Each hantavirus is associated with a different small mammal host, most usually rodents. As a result, the spread and distribution of each virus is closely linked to the ecology of its host.

The majority of reported cases are in East Asia and Northern Europe. Cases are less common in the Americas but can be more severe. In the UK, a small number of cases of HFRS have been diagnosed in those without overseas travel, predominantly from individuals with pet rats. Seoul virus has been detected in pet rats, and occasionally in wild rats in restricted geographical areas of the UK. The overall risk to the general public from Seoul hantavirus is considered very low.

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

Certain occupations are associated with an increased risk of infection with hantaviruses globally, including trapping, forestry, farming, and the military. Exposure to rodent excreta from working with wood piles and entering or cleaning abandoned buildings is also associated with an increased risk of hantavirus infection. The risk of exposure amongst campers, hikers and tourists to endemic areas is generally considered to be low, and can be reduced if contact with rodents is avoided.

Virus	Disease	Rodent host	Distribution
Puumala	HFRS	Bank vole (Myodes glareolus)	Europe
Dobrava	HFRS	Yellow-necked field mouse (Apodemus flavicollis)	The Balkans, Southeast Europe
Hantaan	HFRS	Field mouse (Apodemus agrarius)	Asia
Seoul	HFRS	Rats (Rattus rattus, Rattus norvegicus)	Worldwide (including the UK)
Tula	HFRS	Common vole (Microtus arvalis)	Russia, Europe
Sin Nombre	HCPS	Deer mouse (Peromyscus maniculatus, Peromyscus sonoriensis)	North America,
Andes	HCPS	Long-tail pygmy rice rat (Oligoryzomys longicaudatus)	Argentina, Chile
Araraquara	HCPS	Hairy-tailed bolo mouse (Necromys lasiurus)	Brazil
Choclo	HCPS	Fulvous pygmy rice rat (Oligoryzomys costaricensis)	Panama
Laguna Negra	HCPS	Large vesper mouse (Calomys laucha, Calomys callosus)	Paraguay, Argentina, Bolivia, Peru
Juquitiba	HCPS	Black-footed pygmy rice rat (Oligoryzomys nigripes)	Brazil

Small outbreaks of disease for many hantaviruses have been linked to population blooms in the host reservoir species, for instance, ‘mast years’ (years with increased seed production from trees) often result in a population explosion of small mammals and increased contact with human populations.

Transmission

Animal-human transmission occurs when people come into contact with infected rodents and their droppings or environments contaminated by rodent excreta. It is believed that transmission occurs through inhalation of aerosolised virus particles from rodent excreta (or dust containing the excreta), or by touching mucous membranes with hands that have been contaminated by the virus. Rodent bites are a rare but potential route of transmission.

Human-to-human transmission of hantavirus is very rare and has only been reported with ANDV, please refer to Andes hantavirus: epidemiology, outbreaks and guidance.

Clinical features

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, Tula, 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 can 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 similar to Hantaan virus, although a lower severity has been seen in UK cases. Nephropathia epidemica (NE) is a mild form of HFRS, and is caused by Puumala virus, the most common hantavirus, present in most countries in north-western Europe. NE has an abrupt onset with fever and myalgia, thrombocytopaenia (low blood platelet count) and sometimes myopia (short-sightedness). An acute renal failure can occur, occasionally requiring dialysis. The mortality rate is less than 0.1%. Tula virus is rarely associated with clinical disease, but when this is observed is usually a very mild form of NE and may present with only non-specific febrile symptoms.

Hantavirus cardiopulmonary syndrome (HCPS)

HCPS is rare, with about 300 cases per year reported in the Americas. The incubation period for HCPS is 14 to 17 days and symptoms begin with a short prodrome of fevers and myalgias (muscle aches) lasting 3 to 5 days. Patients also report headache, dizziness/light-headedness, dry cough, stomach and back pains, nausea and vomiting and other gastrointestinal symptoms in this time. Progress to the HCPS can be rapid, with the development of increasing shortness of breath, pulmonary oedema (fluid in the lungs) and cardiovascular shock (very low blood pressure) and patients may need support in an intensive care unit.

The most severe forms of HCPS are associated with Sin Nombre virus, Andes virus, Araraquara virus and Juquitiba virus, which can have a case fatality rate up to 50%. Choclo virus and Laguna Negra virus can be less severe with case fatality rates 12 to 15%.

Diagnosis

In the UK, the Rare and Imported Pathogens Laboratory (RIPL) at UK Health Security Agency (UKHSA) Porton Down is the designated diagnostic laboratory. RIPL offers molecular and serological assays for the detection of acute and convalescent (recovered) hantaviruses cases.

Any suspected case must be discussed with local infection specialists and with the Imported Fever Service (IFS) 24-hour telephone service on 0844 778 8990.

The IFS can advise on whether laboratory testing is indicated, and if so, will provide advice about the sample types required. IFS will also advise on sample collection precautions and transport requirements.

Treatment

There is no proven specific treatment for hantavirus infection and there is no preventative vaccine currently available. Treatment is supportive. Patients with HRFS/HCPS may deteriorate rapidly, and intensive care input should be sought at the earliest sign of worsening condition.

Infection prevention and control for confirmed or suspected cases

Suspected or confirmed ANDV should be managed in line with airborne HCID guidance, please refer to Andes hantavirus: epidemiology, outbreaks and guidance and for HCID guidance and NHS England’s Addendum on high consequence infectious disease (HCID) personal protective equipment (PPE).

Suspected or confirmed infection due to hantaviruses other than ANDV should be managed in line with standard NHS infection control principles.

Advice for reducing risk of infection in endemic regions

The risk of hantavirus infection can be reduced by avoiding exposure to rodents or areas that may be infested with rodents (for example, where droppings are visible) in endemic areas. Hygiene precautions such as washing your hands with soap and water after handling rats or their bedding and cage should be applied.

Basic rural accommodation, such as forest cabins and mountain huts, should be aired before use if the accommodation has been left unoccupied for a prolonged period.

Cabins and potential campsites in endemic areas should not be used if rodents, rodent droppings or rodent nests or burrows are identified. If use cannot be avoided, disinfect areas that have signs of rodents using chemical detergent. Use a mop or wetted cloth as this reduces the potential for aerosolisation. If camping, use a ground sheet and camping mat, and sleep on a camping bed if possible. Observe good hand hygiene by washing hands regularly. If there is a local outbreak, follow public health official advice about avoiding contact with rodents, environmental disinfection and quarantine precautions.

In the UK, infection with Seoul hantavirus from pet rats can be avoided by following guidance available at Reducing the risk of human infection from pet rodents.