Cryptic rabies refers to infection from unrecognized exposure to rabies virus. It is often phylogenetically traced to bats. It is most often seen in the southern United States. Silver-haired bats (Lasionycteris noctivagans) and tricolored bats (Perimyotis subflavus) are the two most common bat species associated with this form of infection, though both species are known to have less contact with humans than other bat species such as the big brown bat. That species is common throughout the United States and often roosts in buildings and homes where human contact is more likely. [1] [2]
Cryptic rabies refers to instances where rabies occurs in an individual with no clear history of exposure to a rabies vector. Determining history of contact, usually via the bite of an infected animal, can be difficult if the patient is unconscious or incoherent by the time an attempt is made to collect patient history. Thus, friends and family are needed to fill in patient history of possible bite exposure. Additionally, bites from a vector can be overlooked, particularly for some small bat species. Bites from a bat can be so small that they are not visible without magnification equipment, for example. Outside of bites, rabies virus exposure can also occur if infected fluids come in contact with a mucous membrane or a break in the skin. Rabies virus has also been transmitted when an infected human unknowingly dies of rabies, and their organs are transplanted to others. [3]
While it has been speculated that rabies virus could be transmitted through aerosols, studies of the rabies virus have concluded that this is only feasible in limited conditions. These conditions include a very large colony of bats in a hot and humid cave with poor ventilation. While two human deaths in 1956 and 1959 had been tentatively attributed to aerosolization of the rabies virus after entering a cave with bats, "investigations of the 2 reported human cases revealed that both infections could be explained by means other than aerosol transmission". [3]
It is not well understood why most, but not all, cases of cryptic bat rabies can be traced to silver-haired bats and tricolored bats, but it is believed that the strain of rabies virus in these species is particularly virulent. [4] [5] [6]
A zoonosis or zoonotic disease is an infectious disease of humans caused by a pathogen that can jump from a non-human to a human and vice versa.
The tricolored bat or American perimyotis is a species of microbat native to eastern North America. Formerly known as the eastern pipistrelle, based on the incorrect belief that it was closely related to European Pipistrellus species, the closest known relative of the tricolored bat is now recognized as the canyon bat. Its common name "tricolored bat" derives from the coloration of the hairs on its back, which have three distinct color bands. It is the smallest bat species in the eastern and midwestern US, with individuals weighing only 4.6–7.9 g (0.16–0.28 oz). This species mates in the fall before hibernation, though due to sperm storage, females do not become pregnant until the spring. Young are born helpless, though rapidly develop, flying and foraging for themselves by four weeks old. It has a relatively long lifespan, and can live nearly fifteen years.
Lyssavirus is a genus of RNA viruses in the family Rhabdoviridae, order Mononegavirales. Mammals, including humans, can serve as natural hosts. The genus Lyssavirus includes the rabies virus traditionally associated with the disease of the same name.
Rabies virus, scientific name Rabies lyssavirus, is a neurotropic virus that causes rabies in animals, including humans. Rabies transmission can occur through the saliva of animals and less commonly through contact with human saliva. Rabies lyssavirus, like many rhabdoviruses, has an extremely wide host range. In the wild it has been found infecting many mammalian species, while in the laboratory it has been found that birds can be infected, as well as cell cultures from mammals, birds, reptiles and insects. Rabies is reported in more than 150 countries and on all continents except Antarctica. The main burden of disease is reported in Asia and Africa, but some cases have been reported also in Europe in the past 10 years, especially in returning travellers.
In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.
Australian bat lyssavirus (ABLV), originally named Pteropid lyssavirus (PLV), is a enzootic virus closely related to the rabies virus. It was first identified in a 5-month-old juvenile black flying fox collected near Ballina in northern New South Wales, Australia, in January 1995 during a national surveillance program for the recently identified Hendra virus. ABLV is the seventh member of the genus Lyssavirus and the only Lyssavirus member present in Australia. ABLV has been categorized to the Phylogroup I of the Lyssaviruses.
Lagos bat lyssavirus, formerly Lagos bat virus (LBV) is a Lyssavirus of southern and central Africa that causes a rabies-like illness in mammals. It was first isolated from a fruit bat from Lagos Island, Nigeria in 1956. Brain samples from the bat showed poor cross-reactivity to rabies antibodies but the virus was found to be closely related to the rabies virus. This was the first discovery of a rabies-related virus. Until this time, rabies was thought to have a single causal agent.
The common vampire bat is a small, leaf-nosed bat native to the Neotropics. It is one of three extant species of vampire bat, the other two being the hairy-legged and the white-winged vampire bats. The common vampire bat practices hematophagy, mainly feeding on the blood of livestock. The bat usually approaches its prey at night while they are sleeping. It then uses its razor-sharp teeth to cut open the skin of its hosts and lap up their blood with its long tongue.
An emergent virus is a virus that is either newly appeared, notably increasing in incidence/geographic range or has the potential to increase in the near future. Emergent viruses are a leading cause of emerging infectious diseases and raise public health challenges globally, given their potential to cause outbreaks of disease which can lead to epidemics and pandemics. As well as causing disease, emergent viruses can also have severe economic implications. Recent examples include the SARS-related coronaviruses, which have caused the 2002-2004 outbreak of SARS (SARS-CoV-1) and the 2019–21 pandemic of COVID-19 (SARS-CoV-2). Other examples include the human immunodeficiency virus which causes HIV/AIDS; the viruses responsible for Ebola; the H5N1 influenza virus responsible for avian flu; and H1N1/09, which caused the 2009 swine flu pandemic. Viral emergence in humans is often a consequence of zoonosis, which involves a cross-species jump of a viral disease into humans from other animals. As zoonotic viruses exist in animal reservoirs, they are much more difficult to eradicate and can therefore establish persistent infections in human populations.
Andes orthohantavirus (ANDV), a species of Orthohantavirus, is a major causative agent of hantavirus cardiopulmonary syndrome (HCPS) and hantavirus pulmonary syndrome (HPS) in South America. It is named for the Andes mountains of Chile and Argentina, where it was first discovered. Originating in the reservoir of rodents, Andes orthohantavirus is easily transmitted to humans who come into contact with infected rodents or their fecal droppings. However, infected rodents do not appear ill, so there is no readily apparent indicator to determine whether the rodent is infected or not. Additionally, Andes orthohantavirus, specifically, is the only hantavirus that can be spread by human to human contact via bodily fluids or long-term contact from one infected individual to a healthy person.
In epidemiology, a disease vector is any living agent that carries and transmits an infectious pathogen to another living organism; agents regarded as vectors are organisms, such as parasites or microbes. The first major discovery of a disease vector came from Ronald Ross in 1897, who discovered the malaria pathogen when he dissected a mosquito.
Rabies is a viral disease that causes encephalitis in humans and other mammals. It was historically referred to as hydrophobia due to the symptom of panic when presented with liquids to drink. Early symptoms can include fever and abnormal sensations at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, violent movements, uncontrolled excitement, fear of water, an inability to move parts of the body, confusion, and loss of consciousness. Once symptoms appear, the result is virtually always death, regardless of treatment. The time period between contracting the disease and the start of symptoms is usually one to three months but can vary from less than one week to more than one year. The time depends on the distance the virus must travel along peripheral nerves to reach the central nervous system.
Almost all human deaths caused by rabies occur in Asia and Africa. There are an estimated 59,000 human deaths annually from rabies worldwide.
In animals, rabies is a viral zoonotic neuroinvasive disease which causes inflammation in the brain and is usually fatal. Rabies, caused by the rabies virus, primarily infects mammals. In the laboratory it has been found that birds can be infected, as well as cell cultures from birds, reptiles and insects. The brains of animals with rabies deteriorate. As a result, they tend to behave bizarrely and often aggressively, increasing the chances that they will bite another animal or a person and transmit the disease.
Airborne transmission or aerosol transmission is transmission of an infectious disease through small particles suspended in the air. Infectious diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant infectious agent may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets. This is the transmission of diseases via transmission of an infectious agent, and does not include diseases caused by air pollution.
Cross-species transmission (CST), also called interspecies transmission, host jump, or spillover, is the transmission of an infectious pathogen, such as a virus, between hosts belonging to different species. Once introduced into an individual of a new host species, the pathogen may cause disease for the new host and/or acquire the ability to infect other individuals of the same species, allowing it to spread through the new host population. The phenomenon is most commonly studied in virology, but cross-species transmission may also occur with bacterial pathogens or other types of microorganisms.
The bat virome is the group of viruses associated with bats. Bats host a diverse array of viruses, including all seven types described by the Baltimore classification system: (I) double-stranded DNA viruses; (II) single-stranded DNA viruses; (III) double-stranded RNA viruses; (IV) positive-sense single-stranded RNA viruses; (V) negative-sense single-stranded RNA viruses; (VI) positive-sense single-stranded RNA viruses that replicate through a DNA intermediate; and (VII) double-stranded DNA viruses that replicate through a single-stranded RNA intermediate. The greatest share of bat-associated viruses identified as of 2020 are of type IV, in the family Coronaviridae.
European bat 2 lyssavirus(EBLV-2) is one of three rabies virus-like agents of the genus Lyssavirus found in Daubenton's bats in Great Britain. Human fatalities have occurred: the naturalist David McRae who was bitten by a Daubenton's bat in Scotland, became infected with EBLV-2a and died in November 2002. It must now be assumed that the virus is present in bats in the UK. Testing of dead bats by MAFF/DEFRA over the last decade indicates that the overall incidence of infection is likely to be very low, although limited testing of live Daubenton's bats for antibodies suggests that exposure to EBLV-2 may be more widespread. Nevertheless, infected bat bites have caused human deaths so appropriate precautions against infection must be taken. The Department of Health’s recommendation is that people regularly handling bats should be vaccinated against rabies. Included in this category are all active bat workers and wardens, and those regularly taking in sick and injured bats. The Statutory Nature Conservation Organisations and the Bat Conservation Trust urge all those involved in bat work to ensure that they are fully vaccinated and that they receive regular boosters. Bats should not be handled by anyone who has not received these vaccinations. Even when fully vaccinated, people should avoid being bitten by wearing appropriate bite-proof gloves when handling bats. Any bat bite should be thoroughly cleansed with soap and water and advice should be sought from your doctor about the need for post-exposure treatment. Further information is available from the SNCOs, the Bat Conservation Trust or the Health Protection Agency (HPA) /Scottish Centre for Infection and Environmental Health (SCIEH).
A feline zoonosis is a viral, bacterial, fungal, protozoan, nematode or arthropod infection that can be transmitted to humans from the domesticated cat, Felis catus. Some of these diseases are reemerging and newly emerging infections or infestations caused by zoonotic pathogens transmitted by cats. In some instances, the cat can display symptoms of infection and sometimes the cat remains asymptomatic. There can be serious illnesses and clinical manifestations in people who become infected. This is dependent on the immune status and age of the person. Those who live in close association with cats are more prone to these infections. But those that do not keep cats as pets are also able to acquire these infections because of the transmission can be from cat feces and the parasites that leave their bodies.
West Caucasian bat lyssavirus (WCBL) is a member of genus Lyssavirus, family Rhabdoviridae and order Mononegavirales. This virus was first isolated from Miniopterus schreibersii, in the western Caucasus Mountains of southeastern Europe in 2002. WCBL is the most divergent form of Lyssavirus, and is found in Miniopterus bats (insectivorous), Rousettus aegyptiacus, and Eidolon helvum. The latter two are both fruit bats. The virus is fragile as it can be inactivated by UV light and chemicals, such as ether, chloroform, and bleach. WCBL has not been known to infect humans thus far.