RABIES By Fatma Khalifa Synonyms Lyssa Hydrophobia Rabies
RABIES By Fatma Khalifa
Synonyms Lyssa Hydrophobia Rabies
Defination • It is highly fatal viral disease of central nervous system. • is a viral zoonotic neuroinvasive disease which causes inflammation in the brain and is usually fatal. • Affected all warm-blood animals. • Transmitted in the saliva of a rabid animals. • Characterized by , fatal encephalomyelitis producing abnormal behaviour as : 1 - Signs of mania. 2 - progressive ascending paralysis.
OR , animals with rabies suffer deterioration of the brain and tend to behave bizarrely and often aggressively, increasing the chances that they will bite another animal or a person and transmit the disease.
Causative agent Rabies is a lethal zoonotic encephalitis disease Caused by : Lyssa virus , Rhabdoviridae family , RNA virus , Neurotropic virus.
Structure of virus Ø Rabies virus is a rod- or bullet-shaped, Ø single-stranded, Ø negative-sense, unsegmented, enveloped RNA virus. Ø The virus genome encodes five proteins.
q. RABV is a negative-stranded RNA virus of the Rhabdoviridae family. q RABV virions [G] are enveloped by a host cellderived membrane and take on a bullet shape of about 200 nm by 80 nm. q. The bullet shape is likely influenced by the constraints of budding and viral uptake q The relatively small RNA genome of the virus (~12 kb) encodes for five proteins: nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and polymerase (L, in reference to the large size of the gene). q. The basic functions of lyssavirus proteins are well-conserved
Transmission
Susceptibility • Any mammal can transmit the rabies virus. The animals most likely to transmit the rabies virus to people include: Pets and farm animals • Cats , Cows , Dogs , Ferrets , Goats , Horses , Camels. Wild animals • Bats , Beavers , Coyotes , Foxes , Monkeys , Raccoons , Skunks , Woodchucks.
Risk factors q. Traveling or living in developing countries where rabies is more common, including countries in Africa and Southeast Asia. q. Activities that are likely to put you in contact with wild animals that may have rabies, such as exploring caves where bats live or camping without taking precautions to keep wild animals away from your campsite. q. Working in a laboratory with the rabies virus. q. Wounds to the head or neck, which may help the rabies virus travel to your brain more quickly.
Pathogensis After inoculation, rabies virus may enter the peripheral nervous system directly and migrates to the brain. or may replicate in muscle tissue, remaining sequestered at or near the entry site during incubation, prior to central nervous system invasion and replication. It then spreads centrifugally to numerous other organs. The case fatality ratio approaches unity, but exact pathogenic mechanisms are not fully understood.
Life cycle In the first phase of the rabies virus (RABV) life cycle, 1 - The virus binds to the cell surface receptors via its glycoprotein and enters by endocytosis. 2 - Subsequently, the viral membrane fuses with the endosomal membrane to release the viral genome (uncoating, ). In the second phase, The encapsidated negative-stranded RNA genome is transcribed by the polymerase complex,
starting with a short uncapped leader RNA (le. RNA), followed by the transcription of 5′ end-capped (cap) and polyadenylated (A) m. RNAs, and their translation into the viral proteins nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G) and polymerase (L). Following replication, the full-length antigenomic RNA is encapsidated in the nucleoprotein along with the genomic RNA. The synthesized antigenome functions as a template for the synthesis of additional copies of genomic RNA. In the last phase, the viral components are assembled and the RABV virions bud and are released, starting a new round of infection
Incubation period The incubation period is exceptionally variable, ranging from fewer than 10 days to longer than 2 years, But , is usually 1– 3 months.
Stages of rabies • Three stages of rabies are recognized in dogs and other animals. • The first stage is a one- to three-day period characterized by behavioral changes and is known as the Prodromal stage. • The second stage is the Excitative stage, which lasts three to four days. It is this stage that is often known as furious rabies due to the tendency of the affected animal to be
• hyperreactive to external stimuli and bite at anything near. • The third stage is the paralytic or dumb stage and is caused by damage to motor neurons. Incoordination is seen due to rear limb paralysis and drooling and difficulty swallowing is caused by paralysis of facial and throat muscles. • This disables the host's ability to swallow, which causes saliva to pour from the mouth. This causes bites to be the most common way for the infection to spread, as the virus is most concentrated in the throat and cheeks, causing major contamination to saliva. • Death is usually caused by respiratory arrest.
saliva to pour from the mouth
Diagnosis • Case history. • Clinical signs. • Direct fluorescent antibody (DFA) test, which looks for the presence of rabies virus antigens in brain tissue.
Negri bodies are eosinophilic , sharply outlined, pathognomic inclusion bodies (2– 10 μm in diameter) found in the cytoplasm of certain nerve cells containing the virus of rabies, especially in pyramidal cells within Ammon’s horn of the hippocampus. They are also often found in the purkinie cells of the cerebellar cortex from postmortem brain samples of rabies victims. They consist of ribonuclear proteins produced by the virus.
cellular inclusions found most frequently in the pyramidal cells of Ammon's horn, and the Purkinje cells of the cerebellum. They are also found in the cells of the medulla and various other ganglia.
Control • • Notification. Isolation. Disinfection. Immunization.
Prevention • To reduce your risk of coming in contact with rabid animals: • Vaccinate your pets. Cats, dogs and ferrets can be vaccinated against rabies. • Keep your pets confined. • Keep your pets inside and supervise them when outside. • This will help keep your pets from coming in contact with wild animals.
• Protect small pets from predators. • Keep rabbits and other small pets, such as guinea pigs, inside or in protected cages so that they are safe from wild animals. These small pets can't be vaccinated against rabies. • Report stray animals to local authorities. • Call your local animal control officials or other local law enforcement to report stray dogs and cats. • Don't approach wild animals. • Wild animals with rabies may seem unafraid of people. It's not normal for a wild animal to be friendly with people, so stay away from any animal that seems unafraid.
• Keep bats out of your home. Seal any cracks and gaps where bats can enter your home. If you know you have bats in your home, work with a local expert to find ways to keep bats out. • Consider the rabies vaccine if you're traveling. If you're traveling to a country where rabies is common and you'll be there for an extended period of time, ask your doctor whether you should receive the rabies vaccine. • This includes traveling to remote areas where medical care is difficult to find.
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