Rabies virus

2021-08-15 10:17 PM

The rabies virus has a bullet-like stick shape, 130-240 nm long and 70.80 nm in diameter. Nucleocapsid symmetric spiral, containing single-stranded RNA

Rabies is a type of encephalitis-meningitis, which is often fatal. The causative agent is a rabies virus of the genus Lyssavirus, in the family Rhabdoviridae.

The properties of the virus

The rabies virus has a bullet-like stick shape, 130-240 nm long and 70-80 nm in diameter. The nucleocapsid is an asymmetric spiral, contains single-stranded RNA, has an outer shell bearing erythrocyte agglutinating spikes, which are glycoproteins in nature.

Rabies virus replicates in many human and animal cell systems (primary cells, diploid cells...) The virus replicates in the cytoplasm, nucleocapsids cluster in clusters in the endoplasmic reticulum. form inclusions, also known as Negri corpuscles.

Rabies virus is less stable, it is sensitive to others, at 56 0 C / 3 min is inactivated.

Rabies virus has only one serotype.

In 1882, Louis Pasteur injected the rabbit brain with a strain of rabies virus isolated from the brain of rabid animals and found that its pathogenicity was weakened when it was transmitted to dogs by the subcutaneous route, this virus strain is called immobilized virus strain, which is different from the new strains of street rabies virus isolated from rabid dogs.

 

The fixed rabies virus strain

The street rabies virus strain

Incubation period

Short, fixed (7 days)

Varies, short or long depending on bite site and virus virulence

Possibility to cause disease

Feebleness

Strong

Creating Negri corpuscles

Are not

Yes (80 - 90%)

Used to produce vaccines

Okay

Are not

Possibility to cause disease

Pathophysiology

The virus is frequently present in the central nervous system and peripheral nervous system of rabid animals. The nerve cells in the sympathetic ganglia are shed, causing the salivary glands to become infected with the virus.

The rabies virus enters the body usually through skin lesions (bites, scratches, licks...). The rabies virus cannot be transmitted through healthy skin, but intact mucous membranes can still allow the virus to penetrate.

The virus replicates locally in the infected area (muscle, connective tissue, and especially Schwann cells of sensory nerves) and advances along afferent nerves to the spinal cord and then to the central nervous system. the central nervous system, multiply and destroy nerve cells of the cerebral cortex, cerebellar cortex, spinal cord. Finally, the virus follows the efferent nerve pathway to the salivary glands. Salivary secretion of the virus begins 1 to 2 days before the first symptoms and lasts a few days in animals. Other tissues can become infected with the virus, such as in the kidneys, spleen, and lungs.

The incubation period is closely related to the site of the bite, the closer the bite is to the CNS, the shorter the incubation period, so there is less time to protect the person bitten before the virus enters. to the nervous system. Having many bites, deep bites, bites in areas with many nerves, the disease is very serious.

Epidemiology

Reservoirs: are warm-blooded animals including wild animals such as foxes, jackals, wolves, ferrets, etc. naturally circulating rabies, or domestic animals such as dogs and cats... Rabies virus has also been found in the salivary glands of some bat species such as blood-sucking bats and insectivorous bats. Bats often carry latent rabies and can shed the virus for a long time. In rabies animals, the virus is present in the nervous system, saliva, urine, lymph nodes, milk, and is very short-lived in the external environment. Therefore, animals with rabies are the sole reservoir of the virus, and indirect viral infection is rare.

Route of transmission: Rabies is transmitted from one animal to another and to humans through bites, scratches, scrapes on the skin ... contaminated with saliva contaminated with the rabies virus.

Subjects infected: humans and warm-blooded animals are susceptible to the disease. In our country, rabies is circulating in most localities due to a large number of dogs, so the number of people bitten by rabies dogs is high, and the number of people who die from rabies also accounts for a significant proportion.

Clinical Manifestations

Rabies in humans

Rabies is an inflammatory disease of the brain - meninges, the incubation period varies depending on the site of the bite and the virulence of the virus, can be from 1-3 months. The onset period is usually a mild infection syndrome, an abnormal sensation at the bite site, and mental instability. The full-blown period has 3 clinical forms:

Convulsions: the most common, the most characteristic sign is fear of water, fear of wind. Patients often die suddenly due to spasms of the respiratory muscles.

Paralysis: starting with mild paralysis on one or both sides or total body paralysis (Landry's syndrome), paralysis of the respiratory muscles leading to the death of the patient.

Dementia: progression is often dangerous.

Once rabies has flared up and died, treatment only has a preventive effect.

Rabies in animals

Symptoms are that the animal is not normal, refuses to eat, or eats inedible things such as torn clothes, brooms ... The barking dog turns into howling because the vocal cords are paralyzed, drool falls, the animal runs around everywhere. where bite a lot, drink a lot of water. Later, respiratory disorders appeared, the dog was thin and paralyzed and then died around 5-7 days.

Laboratory diagnostics

In terms of microbiological diagnosis of rabies in humans, it is rarely done because it is difficult to obtain specimens, otherwise, it has no therapeutic significance. Diagnosis is usually made mainly in animals suspected of being bitten by a human.

Histopathological examination

The specimen is the brain of an animal suspected of having rabies. Negri corpuscles were found in the cytoplasm of neurons, called Negri corpuscles, but 10-15% were not found.

Find viral antigens

Direct immunofluorescence allows detection of rabies virus antigens within hours (fluorescent cytoplasmic inclusions) in nerve cells, especially in the Ammon horn or cerebellum. This is the best method.

Virus isolation

Virus isolation by infusion of bran mash or saliva into the brains of young mice, then detection of rabies virus antigens in dead mouse brain cells by immunofluorescence. It is also common to isolate viruses in cell cultures.

Serological diagnosis has no diagnostic value.

Preventive treatment

Treatment of bites

For bites, there have been many different treatment methods with the aim of clearing the virus or inactivating the virus.

Treat the bite as quickly as possible, the bite can be treated as follows:

Wash with 20% soap solution or with 20% Benzalkonium chloride solution.

Leave the wound open.

Local anesthetic with procaine works to slow the progression of the virus.

When the bite is in danger, inject anti-nausea serum under the skin above the bite.

Preventive treatment with vaccines

Prophylactic use of rabies vaccines is possible and effective if treated correctly after infection.

First-generation vaccines such as the Fermi simple vaccine produced by culturing the virus in the nervous tissues of large animals (medullary or brain) cause severe allergic encephalitis, which can be fatal. Currently, people use vaccines made from the brain of newborn mice such as the Fuenzalida vaccine that do not contain allergic components, so this vaccine does not cause dangerous complications like the first-generation vaccines. Rabies vaccines are also produced in human diploid cell cultures, but the vaccine volume is small and only used for those who need it for prophylactic purposes. Currently, two types of rabies vaccines are used in Vietnam: Fuenzalida (made in Vietnam) and Verorab (made by France).

When standing in front of a person bitten by a dog, you should apply some of the following measures:

If the dog after biting has rabies attack or dies, or is missing, inject rabies antiserum, then treat with vaccine immediately.

If the dog bites, the dog is still alive, but the bite is close to the central nervous system or deep and many places must be injected with the serum, then vaccinate immediately, and monitor the dog, if after 10 days the dog is still normal, stop the injection.

If the dog bite is still normal, the bite is far from the central nervous system, inject anti-rabies serum and monitor the dog, if there are signs of rabies in the dog, it must be vaccinated immediately.

In case of a puppy bite, it must be injected immediately and given the full dose because the signs of rabies in puppies are not as obvious as in large dogs.

Prevention

In humans

For those whose occupations require them to be near animals that may suddenly become rabid (e.g. veterinarians, furriers, foresters, laboratory, diagnostic and research personnel) people use a vaccine against rabies for prophylactic purposes.

In animals

Including many measures, which need to be implemented synchronously and seriously, such as compulsory vaccination for dogs and cats in areas where rabies is endemic, the extermination of rabid dogs, arrest of stray dogs...