5.3 X-Ray Diffraction (XRD)
5.3.3 Experimental Setup
Association between man and animals are there since the begin-ning of earth. Man’s association with animals became more intimate that certain diseases are transmitted from animals to man and vice a versa. Zoonotic diseases are transmissible between man and animals.
Zoonotic diseases spread by contact with infected animals by handling them or living in their premises. Transmission is through direct contact or aerosol spread. Drinking milk from infected animals is another way of getting zoonotic infections. Insects could transfer mechanically or biologically different zoonotic diseases. These diseases are classified as follows:
Zoonoses Animals ßà Man
Anthrapozoonoses Animals à Man (Rabies) Zooanthroponoses Man à Animals( Diphtheria) Cyclozoonoses Animal ßà Man (Hydatidosis,
Taeniosis) Metazoonoses Animals à Man ( through insect
vector: Malaria) Saprozoonoses Animals à Man (through soil)
Anthrax
Anthrax and Brucellosis are two of the many bacterial zoonotic diseases. Anthrax is a disease caused by Bacillus anthracis. It belongs to the genus Bacillus. Organisms belonging to the genus bacillus are gram positive spore forming bacilli, present ubiquitously in all environ-ments. Many of them do not cause disease in man. Anthrax is an im-portant disease of man and animals and it could be used a biological warfare agent.
Bacillus anthracis
The typical organism is a gram positive bacillus, measuring 1x3-4 µm, have square ends and are arranged in long chains. Spores are located in the center of the non motile bacillus. It can grow on ordinary laboratory media like nutrient agar and blood agar. It does not produce haemolysis on blood agar, shows a cut glass appearance, liquefies gelatin.
Anthrax
Anthrax is primarily a disease of sheep, cattle, horse, and many other animals; humans are rarely affected. Infection is acquired by the entry of spores through injured skin or mucous membrane; rarely spores enter the lungs by inhalation. In animals portal of entry is mouth and gastrointestinal tract.
Spores germinate in the tissue at the site of entry, and growth of the vegetative organisms results in the formation of edema. Organisms spread through lymphatics to the blood stream and they multiply in the blood and tissues. Inhalation anthrax is also called wool sorter’s dis-ease. Infection is acquired by the inhalation of spore present on mate-rials from the animal source. Rapid multiplication of the organisms in the tissue is fatal.
Treatment
Penicillin is the drug of choice. The organism is susceptible to macrolids, aminoglycosides, tetracycline and chloramphenicol.
Ciprofloxacin or other fluoroquinalone is recommended for prophy-laxis.
Immunization
Live attenuated bacilli were first used by Louis Pasteur in 1881.
It gave very good protection in domestic animals. Now the Sterne strain of live spore vaccine is used for animal immunization. Live bacterial vaccine is not safe for human use. Alum precipitated Toxoid has been used to immunize the workers at risk of exposure.
EXERCISE Points to remember
1. Different types of zoonoses 2. Anthrax and its implications Self evaluation
1. Define zoonosis
2. Classify different types of zoonosis with example 3. What is anthrax? Give the name of the agent causing it 4. Give the characteristics of B.anthracis
5. Describe the method of prevention of anthrax in animals
Chapter 28
RABIES
Rabies is a zoonotic disease. Animals act as reservoir of infec-tion. Man gets the infection from the animals
Rabies is a lethal form of encephalitis caused by rabies virus, transmitted through the bite of an infected animal usually a dog.
Properties of the virus
l The virus is bullet shaped
l It is covered by a membranous envelope
l Has protruding spikes 10 nm long
l Spike is composed of a single gycoprotein
l The genome is single stranded RNA- is a minus strand RNA
l Genome contains RNA dependent RNA polymerase
l When freshly isolated from a case, the virus is called “street”
virus
o It can multiply in neural and non-neural tissues
l Serial brain to brain passage in rabbits yields a fixed virus o It can not multiply in non-neural tissue
Pathogenesis and Pathology
l Virus is introduced into the tissue by the bite of a rabid animal o Canines
o Bats etc
l Virus multiplies in the muscle or connective tissue
l Infection ascends through the tissue spaces of the sensory nerves to the CNS
l It multiplies in the CNS
l Spreads though peripheral nerves to salivary glands and tissues
l Rabies virus has not been isolated from the blood of an in-fected person
l The incubation period depends on:
o Amount of viral inoculum o Severity of the bite
o The distance the virus has to travel from its point of entry to the brain
o If bitten on the face, higher attack rate and shorter incubation period seen
l There is nerve cell destruction in the cortex, mid brain, basal ganglion, pons and medulla
l It produces cytoplasmic inclusion bodies in nerve cells called Negri bodies.
Clinical features
The incubation period is from 4 to 12 weeks, some times it may be much longer. If the bite wound is in the neck or head the incubation period is shorter
The virus spreads from the wound to the central nervous system through nerves.
Symptoms
The symptoms may be either furious or dumb. In the furious type, the patient shows the symptoms of excitement , with tremor, mus-cular contractions and convulsions. When there is spasm of muscle of swallowing, patients show fear of water and hence the name hydro-phobia is also given to rabies.
In the dumb type of rabies, ascending paralysis is seen involving the muscles of swallowing speech and respiration.
Virus is present in saliva, skin and eyes and brain The disease is always fatal following convulsions.
Epidemiology
Rabies is a natural infection seen in dogs, cats, bats and carnivo-rous animals such as foxes and wolves. Man acquires the infection generally from infected dogs. Virus is present in the saliva of the in-fected dog. Inin-fected dog dies within ten days. If the dog remain healthy for ten days after biting, it can be regarded as being free of the virus at the time of biting. Aerosol infection has been recorded as a result of laboratory accident. Human patients do not seem to be a source of infection.
Diagnosis
Direct demonstration of virus
Specimens such as hair bearing skin from the back of neck, cor-neal impression smears and brain tissue are examined for virus by im-munofluorescence
Intracytoplasmic inclusion body called Negri body can be dem-onstrated by conventional microscopy
Virus isolation
Attempt to isolate the virus from brain tissue, saliva, CSF and urine from patients can be made by inoculating into mice and the animal is observed for convulsions, paralysis and postmortem examinations for Negri bodies in the brain tissue.
Vaccination
Rabies vaccine was first developed by Pasteur in 1885. It con-sisted of virus attenuated by drying the spinal cord of infected rabbits for varying length of time over KOH. Wild rabies virus is called street
virus and attenuated virus is called fixed virus. All vaccines prepared for human use contain inactivated virus.
Now human diploid cell vaccine (HDCV) is used for vaccina-tion. It contains inactivated virus grown on WI38 or MRC-5 diploid human embryo lung cells
EXERCISE Points to remember
1. Rabies is an untreatable disease.
2. The pathogenesis and pathology of rabies.
3. Prevention of rabies.
Self evaluation 1. What is rabies?
2. Give the properties of rabies virus.
3. Describe the pathogenesis and pathology of rabies.
4. State the symptoms of rabies.
5. State the reasons for hydrophobia in rabies.
6. Describe the epidemiology of rabies.
7. Describe the diagnosis of rabies.
8. Describe the prophylaxis against rabies.
Thymus structure: Fig (29.1)
The thymus gland contains (1) cortex and (2) medulla Cortex
The cortex contains epithelial cells. It is densely populated with lymphocytes of various sizes. Most of the lymphocytes in thymus are immature.
Medulla
T lymphocytes mature in the cortex and migrate into the medulla.
They leave the medulla and enter the peripheral blood circulation. Then they are transported to the secondary lymphoid organs.
Function of the thymus gland
1. The primary function of the thymus is the production of Thymic lymphocytes
2. Thymus is the major site for lymphocyte proliferation in the body Chapter 29