Synonyms : Splenic fever, Milzbrand , Charbon,Wool sorter’s disease,Tarka.
It is an acute widespread infectious disease of livestock that occurs throughout the globe. It is considered to be a very serious infectious disease of herbivorous animals. Other animals like goats, horse, pig may get the infection. This is a zoonotic disease and therefore man can contact the infection through infected cattle. The disease has occasionally been recorded in dogs The disease is also known as splenic fever due to the fact that there is extensive enlargement of the spleen (splenomegaly) due to this infection.
The disease is in existence in all parts of the world. In India, the disease is enzootic in nature and occur in almost all the districts of different States. Some districts are considered as anthrax districts (anthrax belts) due to enzootic nature of the disease in those pockets.
Bacillus anthracis. The bacilli are straight, very large rod shaped non- motile, capsulated, aerobic, spore bearing, gram + ve organisms. The organisms remain in chains The capsules are formed in the body of an infected animal. The spores are never formed so long the organisms remain in the circulation. But, when the organisms come out of the body, the spores are formed. The spores may remain viable in the soil for a considerable period of time and for ten years in the infected tissues and cultures. The soil can maintain the organisms in spore stage for years together without endangering the life of animals.
The organisms can be grown on blood agar under aerobic conditions
The Vegetative form of the bacteria can be killed at 60°C for 30 minute\
the spore form cannot be killed with ease. The spore remains resistant 10 100°C for 5 minutes. But, it will be destroyed at 100°C for 10 minutes. In autoclave at 120°C for 15 minutes all the vegetative forms can be kille_ Commonly available chemicals cannot kill the spores. 5% NaOH can effectively destroy the spore contaminated objects
Bacillus anthracis produces three types of toxins. The toxins are. Extracellular in nature. The toxins are:
- Factor-I – Denotes oedema toxin
- Factor-II – Denotes protecting antigen
- Factor-III – Denotes lethal factor.
Most of the food animals are affected with anthrax. No mammals have got absolute natural immunity against anthrax. The most susceptible animals are cattle and sheep. Next in order is horse and pig. Anthrax has been recorded in dogs, though dog is thought to be resistant to anthrax Birds are refractory to natural infection but outbreaks have been reported in chicken. The disease is not uncommon in camels. Anthrax has been reported amongst elephants of India, Siam, Burma and Tanzania Anthrax has been reported in tigers of zoo.
Anthrax is a zoonotic disease. Man occupies an intermediate position between the susceptible group of animals and the relatively resistant group of animals.
Mode of transmission
The anthrax spores have got the ability to remain viable in the soil for a considerable period of time and thus remain as a continuous source of spread to the susceptible animals. Soil borne outbreaks of anthrax occur in a definite season of year in definite pocket. The pH and humidity of the soil have got some clinical bearing on the spread of the disease. It has been pointed out that alkaline soil is a factor for soil borne outbreaks. It is suggested that degeneration of grasses and plants and accumulation of alluvial soil following significant rainfalls and thereafter draught are contributory factors for the propagation of aerobic spore forming organisms. The stream, rivers- and flood may carry the spores from one place to other and thus may spread the disease to the-virgin soil. Carnivore animals may carry the infection to the distant places. Carnivores may contact the infection through ingestion of contaminated carcases. Various flies have been implicated as carrier of infection during the fly breeding seasons. Animals while grazing in the infected pasture pick up the infection through ingestion or through breach in the oral mucosa or skin. The injury of the oral mucosa may help in the entrance of the infection. In a nutshell, the spores are carried from one place to the other by : WATER – AIR CURRENT – VECTOR.On gaining access in the animal’s body, the spores turn into vegetative form and set up the disease process.
Anthrax organism has got three factors viz, oedema factor, protein antigen and lethal factor with which they exert their virulent effect on the-host. None of the factors can act individually. Protein antigen transport oedema factor and lethal factor to the target cells. Protein antigen and oedema factor combination produce oedema and protein antigen and lethal factor combination lead to fatal termination of hosts. The foregoing factors decrease the resistance of the hosts and inhibit the phagocytic activities in them. The poly-D-glutamate capsule of anthrax bacilli is responsible for the interference in opsonization and thus enhances the function of oedema and lethal factors.
On gaining entry the spores are transformed into vegetative form and tend to move towards lymph nodes. From the lymph nodes following multiplication the bacilli enter the blood by way of lymphatic channel. Thus a septicaemic condition of the hosts develop .Bacilli then invade all the body tissues and organs. The bacilli at this stage elaborate toxins and thus produce damaging effect and oedema of tissues. Animal may die at this stage due to shock and acute renal failure. Due to changes in blood components and damage of central nervous tissues, severe anoxia may ensue and this may lead to death .
The presence of antibodies in the host can neutralize the toxin and therefore help the animal to recover from the attack of anthrax.
The clinical findings differ in different species of animals. The incubation period ranges from 2 to 10 days. The disease may appear as per-acute, acute and sub-acute form.
Acute form is predominantly noticed in cattle where the disease occurs in an outbreak, proportion. There is elevation of body temperature (104 to 1O8°e). Animal refuses to eat and there is development of bloat. Animal is extremely depressed. Pulse and respiratory rates are accelerated to a great extent. With the advancement of disease process there is development of muscular tremor. Some animals may show extreme aggressiveness following depression stage. At ‘the end, animal shows distressed breathing. Extreme dyspnoea leads to mouth breathing due to oxygen, hunger. Following death there is oozing of blood from all the natural orifices. The blood used to contain significant number of anthrax bacilli. Death usually takes place within 48 hours.
In per-acute form animals may be found dead without any premonitory signs.
Sub-acute form is characterized by oedema. Oedema is predominantly noticed under the neck, brisket region, thorax, abdomen and flank. The oedema of the thorax and brisket region produces respiratory distress. Jugular pulse is noticed at the terminal stage of the disease. Pregnant cattle may abort. Some may survive for 2 to 3 months.
Man: Anthrax is considered as a zoonotic disease (Tweihons, 1970). Food animals and their products constitute potential danger to those persons whose occupation necessitates handling of animal products or contact with animals. Usually, butchers, skinners, meat retailers, meat inspectors, tanners and veterinarians are the worst victim. The main symptoms in man are the formation of malignant carbuncles and pneumonia due to involvement of skin and lungs.
In anthrax, carcase decomposes rapidly with formation of gas and distension of abdomen. Rigor mortis is absent. Blood and blood stained fluid usually escape from the natural orifices and the visible mucous membranes remain purple in colour. The blood is dark red or black in appearance and does not clot rapidly. Due to lack of oxygen the blood is dark in colour. Yellow gelatinous fluid is found in every part of subcutaneous tissues. Subserous, subepicardial and subendocardial haemorrhages are commonly found. Sero sanguinous fluids may accumulate in the body cavities. The spleen is very much enlarged and soft. In some cases, the spleen is so much enlarged that its capsule gets ruptured. The liver and kidneys are congested. The mucous membrane of the intestine is intensely red in some parts. There is prolapse of rectum. The lungs are congested, swollen and oedematous. In pigs, the changes are mostly confined to pharyngeal region. The connective tissues and lymphatic glands of this region are swollen, oedematous with jelly like appearance.
Animal that dies suddenly with bloody discharges from mouth, nostrils, anus must be suspected to have died of anthrax. The anthrax infected carcase should not be opened. It is generally difficult to demonstrate the anthrax bacilli in the blood during the early stages of the disease. The organisms are present in sufficient numbers in the blood towards the terminal stages of the disease.
Microscopic examination of blood films
Thick blood films of blood sample are to be made on clean glass slide dried in air, fixed slightly with heat and stained with polychrome methylene blue or Giemsa’s stain. Wash in water, dry; examine under oil immersion. Positive blood films stained with Polychrome methylene blue will show the presence of large square ended blue rods in short chains. The Giemsa stained smear will show reddish discolouration of capsules.
A loop full of suspected blood sample is to be streaked on 5% blood agar and nutrient agar plates and the plates are to be incubated aerobically for 18-24 hours at 37°C. Following incubation the plates are to be examined for cultural characteristics compatible with B. anthracis. Positive diagnosis can be arrived based on microscopical and cultural characteristics. In solid media positive cases will show cultural characteristic compatible to B. anthracis viz. absence of motility, very little or no haemolysis medusa head appearance and inverted fir tree appearance on gelatine stab culture
For biological tests, suspension is to be made with small quantity of sterile normal saline from materials like blood from the ear or swab of blood stained discharges. The materials are to be heated at 60°C for 30 minutes in order to kill all the vegetative bacteria. Then 0.5 ml of the suspension is to be injected into the thigh of guineapig subcutaneously. The animal will die in 36-40 hours in positive cases of anthrax. Gelatinous exudates will be found at the site of inoculation. Blood smear of guinea pig will reveal large number of anthrax bacilli.
Vesicular fluid from human lesion
Samples of fluid are to be obtained from cutaneous lesions of the hand, having malignant vesicles with the aid of sterile cular pipettes. Some of the 1 fluid samples may be streaked upon 5% sheep blood and nutrient agar.
Serological test: Ascoli’s test
This is a thermoprecipitation test; this test is employed for the detection of anthrax in hide or tissues. A piece of hide or tissue is boiled in water and extract is obtained. The clear fluid thus obtained is layered on a very narrow precipitating serum. In a positive cases whitish ring appear at the junction of the two fluids.
A fluorescent anti phage staining system for Bacillus anthracis can be performed for its diagnosis.
Anthrax must be differentiated from
- lighting stroke
- black quarter
- haemorrhagic septicaemia
- acute lead poisoning
- snake bite
- Electric injury
- Acute tympany
- Acute lead poisoning
- Prussic acid (HCN) poisoning
- Acute leptospirosis
- Acute infectious anaemia
Per-acute cases of anthrax may not allow any opportunity for rendering treatment due to the obvious reason that the animals die after a very short clinical course. Treatment is always effective provided the cases are attended at the initial stage of the disease. Anthrax bacilli are sensitive to penicillin and other broad spectrum antibiotics. Penicillin 10,000 units per kg body weight twice daily through parenteral route has been proved to be effective against anthrax. Miller (1946) recommended the use of streptomycin @8 to 10 gm in divided doses through intra muscular injection in cattle. Apart from the above, Oxytetracycline, erythromycin, chloramphenicol or sulphonamide have been advocated against anthrax.
Anti anthrax serum @ 100-200 C.c. through intravenous route along with a course of penicillin may be given.
In all cases treatment has to be continued at least for 5-7 days. As a routine measure, a case of anthrax may be brought under the regimen of aqueous penicillin through intravenous route followed by use of procaine penicillin through intramuscular route.
- Control of anthrax in areas free from the disease should be achieved at by preventing the introduction of infected animals.
- The fodder from infected pasture should be destroyed and not to be given to the susceptible animals.
- The disease should be brought under the notice of the regulatory officials in case of an outbreak.
- The strict quarantine arrangement should be made in the anthrax prone areas.
- Care should be taken to destroy the dead body by deep burial with quick lime.
- The adjacent areas of the dead and infected animals should be thoroughly disinfected by applying 3% per acetic acid or 10% caustic soda or 10% formaline. 3% per acetic acid is considered as an efficient sporicide and thus may be applied to the soil for effective sterilization with a dose of 8 lit res per square metre
- Hides, wools, bone meals etc. should be sterilized by gamma irradiation and get certified from competent authority as free from anthrax spores.
- Carcasses should not be opened as it may contaminate the pasture.
- Persons handling the anthrax infected animals should adopt adequate sanitary measures for their own safety.
- Animal clinicians should take care while making blood smear from dead animals
In countries where the anthrax is enzootic in nature there is a need of a continual vaccination programme. Anthrax vaccine should be done annually one to two months prior to anthrax season. In heavily contaminated surroundings two doses of vaccines may be given at 15 to 30 days interval.
Vaccine used : Sterne vaccine