In this article we will discuss about Tetanus in Animals:- 1. Definition of Tetanus 2. Bacteriology in Tetanus 3. Resistance 4. Incidence 5. Animals Susceptible 6. Modes of Infection 7. Pathogenesis 8. Postmortem Lesions 9. Incubation Period 10. Symptoms 11. Course 12. Treatment 13. Antitoxin 14. Immunisation.
Definition of Tetanus:
Tetanus is an acute, infective toxaemic disease arising from wound infection caused by Clostridium tetani and resulting in intoxication of the nervous system with toxins liberated by cl. tetani and characterised by increased reflex irritability of the motor nerve centres and spasmodic contraction of muscles with marked exacerbations.
Bacteriology in Tetanus:
Cl. tetani is a sporulating rod measuring 4µ to 8 µ by 0.3 µ to 0.6 µ with terminal spore giving the rod a drumstick appearance. It possesses flagella distributed all over the surface and is, therefore, motile. It is a strict anaerobe. It stains by the common aniline dyes. Only the wall of the old spore is stained but new spore stains solidly like the bacillus.
Cl. tetani forms an extracellular toxin, both in the body and in culture.
Toxic filtrates contain two toxic substances:
(a) Tetanospasmin which causes muscular spasms and
(b) Tetanolysin — Which causes haemolysis of R. B.Cs. In the body, most of the toxins is absorbed by the motor nerve endings but a small amount may reach the nerve cells through the lymphatics and blood stream.
Tetanus toxin is destroyed in 5 minutes at 65° C. The sporulating organisms may be recognised in films of pus from the wound but they are always found along with other kinds of bacteria.
Resistance of Tetanus:
The bacilli are killed by direct sunlight in 12 days and by diffuse light in 1 to 2 months. In putrefying matter, they remain alive longer and may even multiply for a time.
The spores are killed by boiling water in 10 to 15 minutes, by 5% carbolic acid in 15 minutes, by 1 in 1,000 Corrosive sublimate or 1% HCI in half an hour. By 1% Silver nitrate solution in one minute and 30% Hydrogen peroxide in 10 minutes.
Incidence of Tetanus:
The bacilli lead a saprophytic life in surface layer of the soil, specially in the manure soil, and garden soil and often in the dust of the street. Cultures have remained viable in steel nibs for nearly ten years, spores may remain in the tissue for months. They are also frequently present in the intestinal contents of healthy animals, specially horse tribe, the ingesta of which contaminate the ground and fodder.
Animals Susceptible to Tetanus:
All domesticated mammals including man, specially the horse tribe. One attack does not confer any immunity.
Modes of infection of Tetanus:
By wound infection.
Deep punctures wounds from which oxygen is excluded are much more serious than large superficial wounds, the surfaces of which are exposed to the action of sunlight and fresh air. Lacerated wounds and extensive injuries resulting in much tissue destruction and haemorrhage, particularly if caused by some dirty objects, are favourite sites of infection; but in many cases, the wound may be so small as to be completely overlooked. Picked-up nail wounds, cracked heels, contaminated with tetanus germs are the source of infection. It may also occur from the uterus owing to parturition, during castration, from nose ring, dethroning, navel-ill, docking etc.
Idiopathic tetanus:
In so-called Idiopathic Tetanus, there is no history of injury and no wound is detectable. This probably arises from injury caused by intestinal worms in the alimentary canal.
Pathogenesis of Tetanus:
Healthy animal tissue is not a good medium for the propagation of tetanus bacilli. Toxin-free spores introduced under the skin are inactive; on the other hand, toxin holding cultures even in small quantity give rise to disease.
The spores contain no toxin and when in spite of this, on infection of healthy tissue is caused by spore containing soil, this is due to simultaneous entry of other bacteria, specially pyogenic cocci along with tetanus spores. The pyogenic cocci attack the healthy tissue giving rise to an accumulation of exudates and also through their combining with oxygen produce anaerobic condition which is favourable for tetanus bacilli to grow.
Tetanus bacillus is essentially a parasite of the tissue and remains usually at the seat of entry, where they multiply and elaborate the toxin which is extracellular and carried through blood stream.
Postmortem Lesions of Tetanus:
There is no characteristic lesion of the disease. Secondary oedema, pneumonia or gangrene may be seen.
In the carcass in which fatal tetanus has developed rapidly, the only signs are those of death from asphyxia which comprises of dirty coloured incompletely coagulated blood and small haemorrhages in the serous and mucous membranes, hyperaemia and acute oedema of the lungs.
Incubation Period of Tetanus:
In natural infection, 4 to 14 days, sometimes longer and exceptionally after 24 hours. On the other hand, not till several weeks or months after healing of the primary injury. These variations are due to nature of wounds and severity of infection.
Symptoms of Tetanus:
The onset is gradual in the form of stiffness, which may be general or local. In the early stages, the symptoms are not distinct. After about 24 hours, the syndrome is usually distinctive.
Horses stand rigidly with stiff gait and spread out feet with the neck stretched forward and the head held motionless in one position. If they are made to walk, they do it with great difficulty.
Areas of the body may break out in patchy sweating or practically the whole of the trunk may be bathed in perspiration. The tail is immobile and somewhat raised and generally drawn to one side. Tonic spasms of the skeletal muscles are extensive, beginning first at the head or in the muscles of the hind limbs they, extend until the condition becomes generalised.
Special difficulty is shown in turning which the horse performs with the body held stiffly, still more difficult is backing, which is often impossible. Attempt to raise the foot may make the animal fall down owing to the disturbance of equilibrium.
At the beginning, the pulse and temperature are normal; towards the end of a fatal attack, the temperature may rise up to (110° F°C) and continues to rise further even after death. The peristalsis is diminished and bowels are constipated.
The erect ears, narrowing of the palpebral fissures, the immobile eyes with dilated pupils, partially covered by the protruding nictitating membrane (which become pronounced when the head is abruptly raised or when the head is raised by the animal itself when startled). The dilated nostrils and the spasmodically closed mouth with expression suggesting great anxiety are characteristics of this disease.
On account of the spasm of the pharyngeal muscles and consequent difficulty in swallowing, the saliva accumulates in the mouth and there may be drooling of ‘saliva in long threads. Spasms of the muscles of the neck, back and tail cause a stiff and extended position of the head and neck (Orthotonus), and an elevation of the tail; occasionally the head and neck may be drawn backward (Opisthotonus) and the tail may be curved laterally.
The muscles of the quarters can be felt either hard or board like. The spinal column may be twisted, arched or hollowed. When the spinal column and trunk are generally bent to one side or the other, the condition is known as left or right “pleurosthotonos”.
Owing to the initially increased reflex excitability, severe increase of the spasmodic condition is caused by slight stimuli such as light touch, a noise, a ray of light or an attempt to walk, so that the affected animal may fall down. In protracted cases, the muscular spasms periodically subside, so that the animal can move more freely till another attack of spasms again renders it immobile.
Owing to the spasms of the abdominal and inter-costal muscles, the interchange of gases in the lungs is not free sufficiently, consequently symptoms of deficient oxygenation of blood soon appear, such as cyanosis of the mucosa, hyperaemia and later acute oedema of the lungs with rales, heard over the trachea and thorax.
Although the appetite is usually well-maintained, lockjaw (trismus) renders feeding difficult, if not impossible. The food is chewed noisily and swallowed with difficulty, but it usually remains in the mouth and is expelled later by coughing. During the course of an attack, feces and urine are usually withheld. On account of long retention and because of the absorption, the urine is more concentrated and of higher Sp. Gr.
In fatal cases, the animal, which has been continually standing, collapses and falls to the ground and in a short time dies with intensely increased muscular spasms. The immediate cause of death may be exhaustion, asphyxia or hypostatic or aspiration pneumonia.
In cattle and sheep:
The symptoms are very similar to those of the horse, trismus and protrusion of the jaw being well-marked. Muscular stiffness is severe, flatulence and tympany are observed and the tail may be outstretched. In sheep, standing is impossible, -the affected animals lie on their sides.
In swine:
Swine are usually affected with generalised tetanus.
In dogs:
Owner may notice something peculiar about the eyes and mouth and either stiffness or lameness. Later, the limbs are usually stretched out as far from each other as possible, and opisthotonus is seen. Squinting and grinning are common and trismus is not always in evidence. When it is present it is complete and death follows practically always .
Course for Tetanus:
Death usually occurs in 3 to 10 days from the appearance of the first symptoms but it may sometimes be fatal in 1 to 2 days.
Treatment of Tetanus:
The sick animal should be well- housed and placed in a quiet place with a soft ground, otherwise soft bedding must be provided. The animal should be protected from loud noises, direct sunlight and from unnecessary examination and handling.
Soft, easily digestible green food and mash should be given to the animal together with fresh water if the animal does not feel difficulty in eating. When mastication is impeded by trismus, flour or bran gruel with treacle should be given. The feeding and drinking vessels should be placed in a level with the head. In severe trismus, artificial feeding must be resorted to 1/2 kg of cane sugar with a handful of salt to a bucket of water (lukewarm) per rectum, T. D. if necessary.
Retention of feces may be treated by back recking or by enema of soap water and retention of urine by pressure of the bladder or, if necessary, by passing the catheter.
On account of their antispasmodic action, the following drugs may be tried to quieten the animal:
Chloral Hydrate:
3 vii to 3 xii (28ml to 48 ml.) in solution per rectum once a day. Hexamine has been recommended for its apparent property of rendering the damaged tissues more permeable to antitoxin. Muscle relaxants such as promazine may be administered.
Subcutaneous or intramuscular injection of Mag sulph has proved to be very efficacious in tetanus. Dawson recommends subcutaneous, injection 40 ml of Mag sulph (20 ml on each shoulder). This is to be repeated after 3 hours and then twice daily for 12 days, when the dose should be reduced to 20 ml once daily and continued till 18th day. This is for severe cases.
In milder case, 40 ml (20 ml on each side) once a day for 10 days or longer, if necessary. Abscess formation is likely to occur at the sites of injection. To prevent this, the solution to be injected must be at body temperature and the parts fomented after the injection.
The main principles in the treatment of tetanus are to eliminate causative bacteria and neutralise the residual toxin.
Cl. tetani is susceptible to the effects of penicillin and large doses — 1,00,000 i.u. subcut, followed by 4 injections or more every 6 hours, concurrently with antitoxin serum—is suggested.
Strict attention must be given to the wounds if detected which should be thoroughly cleaned of all dead tissues and discharges and irrigated with a highly potent antiseptic such as 1% Silver nitrate, Perchloride of mercury, 8% chlorine, 5% Tine, iodine, Formalin and Hydrogen peroxide which are very useful agents.
Tetanus Antitoxin:
Which is also known as Antitetanus serum may be used as a curative agent, but this must be used as early as possible but is of little value once signs have appeared.
Large doses should be injected 30,000 to 60,000 i.u. should be given intravenously or by other routes daily until improvement occurs.
Daily doses of Tetanus antitoxin given epidurally for Tetanus in horses is advocated as the treatment of choice. It is also recommended to inject antitoxin around the site of infection when this is established.
Immunisation for Preventing Tetanus:
1. Active Immunisation:
(a) With Tetanus toxin detoxicated by formalin and named as Formon-Toxoid in dose of 10 ml for horse and cattle given sub-cut and repeated after an interval of 1 month. A strong immunity is apparent 14 days after the second injection, which lasts for about a year and may be still prolonged for another year by a further injection at the end of the 1st year.
(b) With Tetanus alum-toxoid made by precipitating tetanus toxoid with Potas. Alum in doses of 10 ml given subcut twice at an interval of a month. The immunity of this injection is also reported to be one year.
2. Passive Immunisation:
Highly potent Antitoxic immuned serum prepared from the horses and commonly known as Antitetanic serum is protective against tetanus infection but the resulting immunity lasts only for a few weeks, hence it is usually used as a prophylactic agent when an infection is suspected in any animal or when an infection is expected, such as may happen after operations. The effects are better, the greater the number of Antitoxin units injected. The dose is 5,000 to 15,000 I.U. according to the age and size of the animal.