Rabies is a viral, zoonotic disease (able to be passed from animals to humans), which primarily affects carnivores (although can affect any mammal) and damages the central nervous system (being neurotropic; tending to attack or affect the central nervous system) and brain. It is also a notifiable disease (it is required by law to be reported to the government - specifically Animal Health and Plant Agency, APHA). Once clinical signs appear, the disease is fatal [1], with death occurring within around 10 days [2] (from three to seven days with most species, with only dogs potentially surviving to ten days) [3]. The virus is typically referred to by the animal which transmitted the disease (which acted as the vector); if it was transmitted between dogs it would be canine rabies, whereas if a dog caught it from a skunk it would be skunk rabies. Dogs are the most important reservoir, carrying the virus and spreading it in an area.
"All rabies reservoirs are also vectors of the virus, but not all vectors are reservoirs." [4]
Reservoirs being a host organism that can harbour a pathogen indefinitely with no ill effects, and vector being an organism which does not cause disease itself but spreads infection by transferring pathogens between hosts. This means that an animal carrying the virus, even if it remains healthy, will still be infectious and spread the disease to others (be it species or individuals of its own species, depend on its reason for not being affected). However not all those carrying the disease, to spread it on to others, will be unharmed by it.
Causes
Rabies is caused by a virus of the genus Lyssavirus in the family Rhabdoviridae. In general, each variant of the virus is transmitted between members of the same species. Transmission occurs in coming into contact with the saliva of in infected animal, typically by biting, to open wounds or unprotected membranes (i.e. eyes and mouth). The incubation period of rabies is highly variable, typically developing in dogs within 28-80 days of exposure to the disease [5], with signs of illness potentially becoming apparent in any time between 10 days, to months to years after infection. [6]
"The virus travels via the peripheral nerves to the spinal cord and ascends to the brain. After reaching the brain, the virus travels via peripheral nerves to the salivary glands. If an animal is capable of transmitting rabies via its saliva, virus will be detectable in the brain." [7]
Symptoms & Diagnosis
General symptoms for the disease among all animals include a sudden change in temperament or behaviour (i.e. a typically docile dog becoming aggressive unprovoked, or vice versa), as well as progressive paralysis, irritability, snapping at the air, loss of appetite, eating of inedible items (i.e. sticks or rocks), seeming depressed, remaining quiet or acting nervousness. Wild animals may appear tame, losing their fear of humans, and nocturnal species may be seen during the daytime.
There are two ways in which rabies may present itself, either making the animal aggressive or paralytic.
In the aggressive form, animals will become irritable, attack at the slightest provocation, viciously use teeth, claws, horns or hooves, losing caution or fear. They may have dilated pupils, showing signs of anxiety and alertness. As the disease progresses in this form, seizures and muscular incoordination may occur, with death being caused by paralysis.
In the paralytic form, the disease may manifest as the inability to swallow, profuse salivation, paralysis of the throat, tongue and lower jaw (which may hang down, particularly in dogs), ataxia (the loss of full control of bodily movements). In this form the animal is more subdued, less inclined to bite, with the paralysis spreading to the entire body until the animal falls into a coma, dying within a few hours.
As well as those above, other species may have additional symptoms.
Cattle: May stop producing milk, bellow, grind their teeth, become more alert, attack other animals, lose their balance and finally be unable to rise before becoming comatose.
Sheep: Often seen in multiple animals in a flock (suggesting a rabid animal attack), appearing restless and then depressed.
Pigs: May hide, kill piglets and be increasingly more dull.
Horses: Displays the furious or depressed form, the former in which the animal displays pronounced excitation. Can become extremely agitated, may have self-inflicted wounds, or roll (meaning it may be interpreted as colic).
Foxes and Coyotes: May invade gardens and houses, attacking animals and humans, or similar abnormal behaviour (i.e. attacking a porcupine or hedgehog, this being relevant to most wild animals).
Due to the similarity of rabies to various other diseases, diagnosis is typically done in a laboratory.
"Immunofluorescence microscopy on fresh brain tissue, which allows direct visual observation of a specific antigen-antibody reaction, is the current test of choice. When properly used, it can establish a highly specific diagnosis within a few hours. Brain tissues examined must include medulla oblongata and cerebellum (and should be preserved by refrigeration with wet ice or cold packs)." [8]
Treatment
As rabies is zoonotic and a notifiable disease, the actions taken following diagnosis are similar to those for Foot-and-Mouth. However they are more severe, considering rabies has the highest case fatality of any infectious disease [9]. As with many notifiable diseases, a risk assessment is taken, which considers the prevalence of rabies in the area, the particular species involved, whether exposure was sufficient for infection to occur, etc. It is recommended by the NASPHV (National Association of State Public Health Veterinarians) that an unvaccinated domestic animal (i.e. cat, dog, ferret) exposed to raabies be vaccinated immediately, or placed in strict isolation (meaning no contact from humans or animals) for six months, receiving a vaccination against rabies one month before being released. [10][11] No vaccine is approved for use on wildlife.
Mainly prevention is attempted with this disease, in terms of mass immunisations (particularly stray dogs), euthanasia of any animals with clinical signs or having been bitten by a rabid animal, quarantine and continued vaccination of young dogs. (Prevention mainly focuses on dogs, due to their importance in the spread of disease as a reservoir).
"Any healthy domestic dog, cat, or ferret, whether vaccinated against rabies or not, that exposes (bites or deposits saliva in a fresh wound or on a mucous membrane) a person should be confined for 10 days; if the animal develops any signs of rabies during that period, it should be euthanised and its brain promptly submitted for rabies diagnosis. If the dog, cat, or ferret responsible for the exposure is stray or unwanted, it may be euthanised as soon as possible and submitted for rabies diagnosis." [12]
References - provided general understanding of the disease; including symptoms, causes and treatments
Overview of Rabies: Rabies: Merck Veterinary Manual
http://www.merckmanuals.com/vet/nervous_system/rabies/overview_of_rabies.html
- Information, observed clinical signs and the fatality of the disease [1]
- Quote, link between vectors and reservoirs of rabies [4]
- Data, incubation period in dogs [5]
- Quote, travel of the disease to the brain along the central nervous system [7]
- Quote, diagnosis of rabies in a laboratory [8]
- Information, regarding NASPHV treatment of animals exposed to rabies [11]
- Quote, treatment of domestic animals with suspected rabies [12]
Rabies Disease in Animals
https://www.daff.qld.gov.au/animal-industries/animal-health-and-diseases/a-z-list/rabies
- Data, time between clinical signs and death [2]
- Data, time between clinical signs and infection [6]
DEPI - Rabies and Australian Bat Lyssavirus
http://www.depi.vic.gov.au/agriculture-and-food/pests-diseases-and-weeds/animal-diseases/general-livestock-diseases/rabies-and-australian-bat-lyssavirus
- Data, time between clinical signs and death, for most species (including dogs) [3]
Compendium of Animal Rabies Prevention and Control, 2011: National Association of State Public Health Veterinarians, Inc. (NASPHV)
http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6006a1.htm
- Information, fatality of rabies [9]
Rabies: Scientific Basis of the Disease and Its Management
https://books.google.co.uk/books?id=C-U1LFK5zagC&pg=PA526&lpg=PA526&dq=NASPHV+recommends+that+any+unvaccinated+dog,+cat,+or+ferret+exposed+to+rabies+be+euthanized+immediately&source=bl&ots=WeaW-iTmS2&sig=yEI873f05kLuHNDKVWZ_ErAOcJI&hl=en&sa=X&ei=WRXEVIm5M-zd7Qa754HgBA&ved=0CCoQ6AEwAQ#v=onepage&q=NASPHV%20recommends%20that%20any%20unvaccinated%20dog%2C%20cat%2C%20or%20ferret%20exposed%20to%20rabies%20be%20euthanized%20immediately&f=false - Information, regarding NASPHV treatment of animals exposed to rabies [10]
CDC - Rabies
http://www.cdc.gov/rabies/
Charlotte O'Connor
"All rabies reservoirs are also vectors of the virus, but not all vectors are reservoirs." [4]
Reservoirs being a host organism that can harbour a pathogen indefinitely with no ill effects, and vector being an organism which does not cause disease itself but spreads infection by transferring pathogens between hosts. This means that an animal carrying the virus, even if it remains healthy, will still be infectious and spread the disease to others (be it species or individuals of its own species, depend on its reason for not being affected). However not all those carrying the disease, to spread it on to others, will be unharmed by it.
Causes
Rabies is caused by a virus of the genus Lyssavirus in the family Rhabdoviridae. In general, each variant of the virus is transmitted between members of the same species. Transmission occurs in coming into contact with the saliva of in infected animal, typically by biting, to open wounds or unprotected membranes (i.e. eyes and mouth). The incubation period of rabies is highly variable, typically developing in dogs within 28-80 days of exposure to the disease [5], with signs of illness potentially becoming apparent in any time between 10 days, to months to years after infection. [6]
"The virus travels via the peripheral nerves to the spinal cord and ascends to the brain. After reaching the brain, the virus travels via peripheral nerves to the salivary glands. If an animal is capable of transmitting rabies via its saliva, virus will be detectable in the brain." [7]
Symptoms & Diagnosis
General symptoms for the disease among all animals include a sudden change in temperament or behaviour (i.e. a typically docile dog becoming aggressive unprovoked, or vice versa), as well as progressive paralysis, irritability, snapping at the air, loss of appetite, eating of inedible items (i.e. sticks or rocks), seeming depressed, remaining quiet or acting nervousness. Wild animals may appear tame, losing their fear of humans, and nocturnal species may be seen during the daytime.
There are two ways in which rabies may present itself, either making the animal aggressive or paralytic.
In the aggressive form, animals will become irritable, attack at the slightest provocation, viciously use teeth, claws, horns or hooves, losing caution or fear. They may have dilated pupils, showing signs of anxiety and alertness. As the disease progresses in this form, seizures and muscular incoordination may occur, with death being caused by paralysis.
In the paralytic form, the disease may manifest as the inability to swallow, profuse salivation, paralysis of the throat, tongue and lower jaw (which may hang down, particularly in dogs), ataxia (the loss of full control of bodily movements). In this form the animal is more subdued, less inclined to bite, with the paralysis spreading to the entire body until the animal falls into a coma, dying within a few hours.
As well as those above, other species may have additional symptoms.
Cattle: May stop producing milk, bellow, grind their teeth, become more alert, attack other animals, lose their balance and finally be unable to rise before becoming comatose.
Sheep: Often seen in multiple animals in a flock (suggesting a rabid animal attack), appearing restless and then depressed.
Pigs: May hide, kill piglets and be increasingly more dull.
Horses: Displays the furious or depressed form, the former in which the animal displays pronounced excitation. Can become extremely agitated, may have self-inflicted wounds, or roll (meaning it may be interpreted as colic).
Foxes and Coyotes: May invade gardens and houses, attacking animals and humans, or similar abnormal behaviour (i.e. attacking a porcupine or hedgehog, this being relevant to most wild animals).
Due to the similarity of rabies to various other diseases, diagnosis is typically done in a laboratory.
"Immunofluorescence microscopy on fresh brain tissue, which allows direct visual observation of a specific antigen-antibody reaction, is the current test of choice. When properly used, it can establish a highly specific diagnosis within a few hours. Brain tissues examined must include medulla oblongata and cerebellum (and should be preserved by refrigeration with wet ice or cold packs)." [8]
Treatment
As rabies is zoonotic and a notifiable disease, the actions taken following diagnosis are similar to those for Foot-and-Mouth. However they are more severe, considering rabies has the highest case fatality of any infectious disease [9]. As with many notifiable diseases, a risk assessment is taken, which considers the prevalence of rabies in the area, the particular species involved, whether exposure was sufficient for infection to occur, etc. It is recommended by the NASPHV (National Association of State Public Health Veterinarians) that an unvaccinated domestic animal (i.e. cat, dog, ferret) exposed to raabies be vaccinated immediately, or placed in strict isolation (meaning no contact from humans or animals) for six months, receiving a vaccination against rabies one month before being released. [10][11] No vaccine is approved for use on wildlife.
Mainly prevention is attempted with this disease, in terms of mass immunisations (particularly stray dogs), euthanasia of any animals with clinical signs or having been bitten by a rabid animal, quarantine and continued vaccination of young dogs. (Prevention mainly focuses on dogs, due to their importance in the spread of disease as a reservoir).
"Any healthy domestic dog, cat, or ferret, whether vaccinated against rabies or not, that exposes (bites or deposits saliva in a fresh wound or on a mucous membrane) a person should be confined for 10 days; if the animal develops any signs of rabies during that period, it should be euthanised and its brain promptly submitted for rabies diagnosis. If the dog, cat, or ferret responsible for the exposure is stray or unwanted, it may be euthanised as soon as possible and submitted for rabies diagnosis." [12]
References - provided general understanding of the disease; including symptoms, causes and treatments
Overview of Rabies: Rabies: Merck Veterinary Manual
http://www.merckmanuals.com/vet/nervous_system/rabies/overview_of_rabies.html
- Information, observed clinical signs and the fatality of the disease [1]
- Quote, link between vectors and reservoirs of rabies [4]
- Data, incubation period in dogs [5]
- Quote, travel of the disease to the brain along the central nervous system [7]
- Quote, diagnosis of rabies in a laboratory [8]
- Information, regarding NASPHV treatment of animals exposed to rabies [11]
- Quote, treatment of domestic animals with suspected rabies [12]
Rabies Disease in Animals
https://www.daff.qld.gov.au/animal-industries/animal-health-and-diseases/a-z-list/rabies
- Data, time between clinical signs and death [2]
- Data, time between clinical signs and infection [6]
DEPI - Rabies and Australian Bat Lyssavirus
http://www.depi.vic.gov.au/agriculture-and-food/pests-diseases-and-weeds/animal-diseases/general-livestock-diseases/rabies-and-australian-bat-lyssavirus
- Data, time between clinical signs and death, for most species (including dogs) [3]
Compendium of Animal Rabies Prevention and Control, 2011: National Association of State Public Health Veterinarians, Inc. (NASPHV)
http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6006a1.htm
- Information, fatality of rabies [9]
Rabies: Scientific Basis of the Disease and Its Management
https://books.google.co.uk/books?id=C-U1LFK5zagC&pg=PA526&lpg=PA526&dq=NASPHV+recommends+that+any+unvaccinated+dog,+cat,+or+ferret+exposed+to+rabies+be+euthanized+immediately&source=bl&ots=WeaW-iTmS2&sig=yEI873f05kLuHNDKVWZ_ErAOcJI&hl=en&sa=X&ei=WRXEVIm5M-zd7Qa754HgBA&ved=0CCoQ6AEwAQ#v=onepage&q=NASPHV%20recommends%20that%20any%20unvaccinated%20dog%2C%20cat%2C%20or%20ferret%20exposed%20to%20rabies%20be%20euthanized%20immediately&f=false - Information, regarding NASPHV treatment of animals exposed to rabies [10]
CDC - Rabies
http://www.cdc.gov/rabies/
Charlotte O'Connor