RABIES EPIDEMIOLOGY Dr Navya Assistant Professor Department of

RABIES- EPIDEMIOLOGY Dr Navya Assistant Professor Department of Community Medicine Yenepoya Medical College

SPECIFIC LEARNING OBJECTIVES At the end of class the students should be able to 1. Explain the agent factors causing rabies 2. Understand the host factors of rabies 3. Describe the clinical features of rabies 4. Explain the types of rabies in dogs

Definition � Hydrophobia � Zoonotic disease- primarily – dogs, cats, jackals, wolves. � Acute � Highly fatal � Viral disease of central nervous system � Caused by- Lyssavirus type 1 � Only communicable disease of man – always fatal

Geographic Distribution � Enzootic and epizootic disease � Some countries – achieved “rabies free”- vigorous campaigns of elimination � Some countries – disease never introduced � Geographic boundaries – major role- water � Majority of cases- rural areas of Africa & Asia- 55, 000 deaths � 20, 000 from India

Epidemiology � Rabies - >150 countries and territories � Carnivorous and bat species – natural reservoir � Rabies – dogs – 99%

Rabies Free Countries � Rabies free country : no case of indigenously acquired rabies – man / animal – 2 years v Australia v China (Taiwan) v Cyprus v Iceland v Ireland v Japan v Malta v New Zealand v UK v Islands of western Pacific v India – union territory of Lakshadweep and Andaman and Nicobar

Epidemiological Determinants 1) Agent Factors : � Agent – Lyssavirus type 1 - neurotropic RNA virus � Street Virus – Recovered from naturally occuring cases Pathogenic for all mammals Long Incubation Period (20 -60 days ) � Fixed Virus – Short incubation period (4 -6 days ) Used in preparation of antirabies vaccine Does not produce negri bodies � Source Of Infection : Saliva of rabid animals Dogs and cats – virus – saliva – 3 -4 days before onset of clinical signs and symptoms and during illness till death

2) Host Factors : � All warm blooded animals – susceptible � Man – dead end infection � Age group – 1 - 24 yrs of age � Higher risk – Laboratory staff working with rabies virus Veterinarians Dog Handlers Hunters Field naturalists

3) Modes Of transmission : � Deep Bite or Scratch – infected animal � Main Host and Transmitter- Dog- rabies death – Asia and Africa � Other hosts – Bats foxes raccoons skunks deaths rare jackals mongooses � Bats – deaths – USA and Canada � Transmission – infected saliva comes in contact with human mucosa or fresh skin wounds

4) Incubation Period : � Highly variable � Commonly 1 -3 months following exposure � Depends on – site of bite severity of bite number of wounds amount of virus injected species of animal protection provided by clothing Treatment undertaken � Incubation shorter- severe exposures, bites on face, head. neck, upper extremities and bites – wild animals

� Pathogenesis : Virus replication in muscle or connective tissues attachment to nerve endings entry into peripheral nerves infection spreads centripetally towards CNS following infection of CNS disease spreads centrifugally skeletal and myocardial muscle, adrenal glands, skin salivary glands invasion

Clinical features : � Prodromal Symptoms – 3 to 4 days : 1) headache 2) malaise 3) sore throat 4) slight fever � Pain or tingling at the site of bite – 80% of the patients- only specific prodromal symptom

Clinical features : � Stimulation of : Sensory system Motor system Sympathetic system Mental changes � Intolerant – noise, bright light, cold draught of air (sensory) � Aerophobia and hydrophobia - pathognomic of rabies � Fanning – current of air across face –violent spasms of pharyngeal and neck muscles

Clinical features : � Examination: – increased reflexes and muscle spasms (motor) -Dilatation of pupil, increased perspiration, salivation and lacrimation (sympathetic) - Fear of death, anger, irritability and depression (mental changes )

Clinical features : � Symptoms – progressively aggravated � All attempts – swallow- unsuccessful � Later stage – mere sight/ sound of water – provoke spasm – muscles of deglutition � Duration of illness is 2 to 3 days � Death can be abrupt – during one of the convulsions or paralysis and coma � Till date only 3 survivors

RABIES IN DOGS � 90% of human rabies death – caused by dogs � Incubation Period – 3 -8 weeks � Clinical Picture : 2 types a) Furious rabies( mad dog syndrome ) 1. A change in behaviour 2. Running amuck 3. Change in voice 4. Excessive salivation and foaming at the angle of the mouth 5. Paralytic stage

RABIES IN DOGS b) Dumb Rabies : 1. Excitative or irritative stage- lacking 2. Predominantly paralytic 3. Dog withdraws itself from being seen or disturbed 4. Lapses into a stage of sleepiness 5. Dies- 3 days

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