Rhabdoviridae

Rhabdoviridae Bullet-shaped RNA viruse Rhabdoviridae encompasses more than 175 viruses of vertebrates, invertebrates, and plants. Most famous member is rabies virus. It causes one of the oldest and most feared disease

Rhabdoviridae Medium size 70 nm in diameter and 170 nm long Enveloped with large peplomers Helical cylindrical nucleocapsid-giving the virus the bullet (conical) shape Non segmented single-stranded negative-sense RNA Genome is encoding 5 genes.

Structure and genomic organization of Rhabdovirus (VSV) [Principles of Virology, 2000-ASM Press, Washington DC] Structure and genomic organization of Rhabdovirus (VSV)

Rhabdoviridae Classification Four genera Lyssavirus is the most important genus. Rabdovirus has different serotypes Each of these viruses is considered capable of causing rabies-like disease in animals and humans

What is a Fixed Virus One whose virulence and incubation period have been stabilized by serial passage and remained fixed during further transmission. Rabies virus that has undergone serial passage through rabbits, thus stabilizing its virulence and incubation period and called as fixed virus

Electron Micrographs of Animal Rhabdoviruses Batvirus - negri bodies brain VSV- ocassional elongated form of virion Bovine ephemeral fever virus Sawgrass virus –isolated from tick-unassigned Figure 39-1 Electron Micrographs of selected animal rhabdoviruses. A: Lyssavirus, Lagos bat virus. A typical Negri body (N) in the brain, with budding virions (*42,000). B: Vesiculovirus, vesicular stomatitis virus. Occasional anomalous elongated form of the virus (*35,000). C: Ephemerovirus, bovine ephemeral fever virus. Isolated from a cow in Australia, 1969. Late infection of VERO cell (*110,000). D: Unassigned, sawgrass virus. Isolated from a tick in Florida (*137,500). (Photographs courtesy of Sylvia Whitfield, CDC, NCID, DVRD, VRZB.)

RABIES VIRUS (RV)

Epidemiology Rabies can infect all warm-blooded animals, and in nearly all animals, the infection is fatal. Dogs are the most important source of human rabies infection. Disease is worldwide, except Japan, United Kingdom, Antarctica, Hawaii and some Caribbean islands.

Epidemiology Bat Rabies in USA Worldwide, 40,000 to 50,000 people die of rabies/year approx 10 million receive post-exposure treatment. Bats in USA and Europe is the source of most human rabies cases. In many cases there is no history of bite.

RV Pathogenesis Transmitted by bite or scratch from a rabid animal. However, in bat caves the infectious virus concentration may be high resulting in aerosol transmission. Incubation period: 14 to 90 days (in humans can be more than 2 years after exposure).

Development of overt rabies depends on: Rabies as a CNS disease Development of overt rabies depends on: (a) Location of the bite – virus must enter the peripheral nerves to travel to brain (b) Severity of bite (c) Species of animal involved (E.g. foxes carry up to 106 infectious particles of rabies virus/ml of saliva)

RV Pathogenesis RV enters peripheral nerves through sensory and motor nerve endings – primarily through neurotransmitter acetylcholine as receptor. Also uses gangliosides and phospholipids.

Sequential event following Rabies virus infection in a dog

RV Pathogenesis Virus enters the brain through the limbic system where it replicates extensively – affecting the cortical control of behavior and leading to the furious form of disease. As the virus continues to spread within the CNS, it reaches the neocortex – resulting in change in clinical disease from fury to dumb or paralytic form.

RV Pathogenesis Virus moves centrifugally from the CNS through the peripheral nerves to: Adrenal cortex Pancreas Salivary glands Virus release In CNS, virus is released from cells by budding into intracytoplasmic membrane. However, in the salivary glands, the virus buds at the apical surface of mucous cells resulting in release of large amounts of virus in saliva. By the time when furious form of disease is evident and animals bite indiscriminately, the saliva is highly infectious.

Clinical disease There is a prodromal (warning) phase before clinical disease that is characterized by change in temperament. NOTE: Higher proportion of dogs, cats, and horses exhibit the furious form than ruminants and lab animals.

Rabies clinical forms: Furious and dumb (paralytic) Furious form – Animal is restless, nervous, aggressive, and dangerous (fearless). Inability to swallow water (hydrophobia), excessive salivation, exaggerated response to light and sound, hyperesthesia (animals commonly bite or scratch themselves). Dumb or paralytic form - As encephalitis progresses, fury gives way to paralysis. Convulsive seizures, depression, coma, and respiratory arrest resulting in death 2 to 14 days after onset of clinical signs.

Majority will succumb to Disease

Rabid dog 4 days after developing clinical signs. Rough hair coat, exudates in the eyes, contracted pupils. Dog paralysed for 4 hr and died 8 hr later

Rabid dog - marked mandibular paralysis

Rabid African ox (furious form) Excessive salivation and loss of body condition (top) Excessive salivation continued until death (below)

Control and prevention Developed countries Stray dog and cat removal and control of movement of pets Immunization of dogs and cats Routine laboratory diagnosis to obtain accurate incidence data Surveillance to assess the effectiveness of all control measures Public education to ensure cooperation Vaccines Inactivated and attenuated RV vaccines are efficacious and safe in animals.

If you are bitten or scratched Tell an health care worker immediately Wash the wound out with soap and water Inform the doctor right away

POSTEXPOSURE PROPHYLAXIS Wound cleaning & treatment

prevention No effective treatment exists. Postexposure Prophylaxis/PEP: 3 steps 1. Wound care: immediate thorough washing with soap and water and a virucidal agent such as povidine-iodine or 1-2% benzalkonium chloride. Shown to be protective if performed within 3 hours of exposure If puncture, swab deeply in wound and around edges

PREVENTION 2. Passive Immunization: Human rabies immunoglobulin (HRIG) 20 IU/kg ASAP, but not longer than 7 days after vaccine given. Infiltrate entire dose around wound, any remaining IG inject IM at a site distant from the vaccine. 3. Human diploid cell vaccine (HDCV): 1 ml (deltoid) on days 0,3,7,14,28. do not give in gluteal. If injected into fat, no antibodies formed.

PREVENTION (HRIG and HDCV: give in different anatomical sites and never in the same syringe. If previously vaccinated - no rabies Ig + vaccine at 0, 3 days only)

Guides to Human Post-exposure Prophylaxis Dog, cats Healthy and available for observation None - Rabid or suspected Rabies Ig + vaccine Unknown Consult PH official Bat Regard as rabid and consider that exposure Rabies Ig + vaccine occurred even if a bite wound is not evident. Unless lab results negative Skunk, fox, coyote Regard as rabid unless proven Rabies Ig + vaccine Bobcat, woodchuck, negative other carnivores Livestock, rodents, Case by case-judgment call rabbits, hares

PREVENTION Pre-exposure vaccination Veterinarians Lab workers working with RV wildlife workers in endemic areas Pre-exposure vaccination regime – 0, 7, 28 days PREVENTION

Lab Diagnosis كشتن حيوان مشكوك به هاري و ارسال سر حيوان به انستيتو پاستور( بريدن سر حيوان بايد بوسيله مامورين دامپزشكي يا بهداشت با استفاد هاز وسائل كامل خفاظتي انجام مي گيرد و در يك كيسه نايلوني ضخيم غير قابل نفوذقرار داده و آن را در يك يخدان پر از يخ قرار مي دهند ). نمونه برداري از بافت مغز با استفاد ه از كيت هاي مخصوص نمونه برداري.

The standard premortem test is a fluorescent antibody test to demonstrate the presence of viral antigen. The standard postmortem test is biopsy of the patient's brain and examination for Negri bodies. Autopsies are rarely performed.

Lab Diagnosis 1. Immunofluorescence - Suspected animals must be killed and brain tissues collected for testing. Diagnosed by direct immunofluorescence showing RV antigens in medulla, cerebellum, or hippocampus.- observe Negri bodies in neurons. 2. RT-PCR – test for RV-RNA in brain 3. Antemortem diagnosis – only done in suspect human cases. Skin biopsy, corneal impressions, or saliva specimens are used. Only positive results are significant in this method because negative results could be due to the fact that these negative results could be due to the fact that these samples are not optimal.

Negri bodies – A gold standard in Diagnosis Inclusion bodies called Negri bodies are 100% diagnostic for rabies infection, but found only in 20% of cases

Negri bodies in Brain Tissue Negri bodies  round or oval inclusion bodies seen in the cytoplasm and sometimes in the processes of neurons of rabid animals after death. Negri bodies are Eosinophilic, sharply outlined, pathognomonic inclusion bodies (2-10 µm in diameter) found in the cytoplasm of certain nerve ..

Light microscopic photograph of multiple intracytoplasmic rabies virus inclusions in a neuron from the brain of a naturally infected bison Light microscopic photograph of multiple intracytoplasmic rabies virus inclusions in a neuron from the brain of a naturally infected bison, revealed by immunohistochemistry (*400). (Photograph courtesy of Michael Niezgoda, CDC, NCID, DVRD, VRZB.)

Negri bodies – collection of RV nuclocapsids in neurons Pathogenesis of rabies virus