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Bacterial Disease - Anthrax

Synonyms

Spleenic fever, Milzbrand, Charbon, Wool sorters disease and Malignant carbuncle.

Introduction

It is a peracute, acute and septicaemic disease of cattle and sheep leading to sudden death.

The extensive enlargement of the spleen given this disease the name spleenic fever.

It is a zoonotic disease spread from infected animals to human during processing of wool and hides.

Etiology

Bacillus anthracis is a pathogenic strain causing anthrax in both human and animals.

It is a non motile, capsulated, aerobic, spore forming, gram positive, organism.

Appears as straight, very large rod shaped, arranged in a small short chain.

The organism has two virulent factors such as, a capsule containing poly D-glutamic acid, which resists the phagocytosis induced by the host immune cells and is coded by the virulent plasmid pxo2, and the triple toxins such as edema factor-1, lethal factor-11 and the protective antigen factor- 111 and these are coded by the plasmid pXo1.

The organism produces spores when exposed to external environment and can live for a prolonged period outside the host in the environment.

Epidemiology

Prevalence of infection

The disease is reported to be recognized from sub Saharan Africa and has worldwide distribution.

The prevalence of the disease depends upon the nature of soil and climatic condition, because, the climatic parameter helps to forecast the "anthrax year".

If the infection is restricted to a particular area is called as "anthrax belts" or enzootic region. During heavy and prolonged rainfall, following a draught, or dry summer, in warm weather and in the temperature at which (>60F /15 ° C) formation of spores, vegetative proliferation with the production of disease or the outbreak occurs.

In African countries, every summer with a heavy rain fall is followed by a devastating occurrence of anthrax.

In India it is enzootic.

Economic impact

Mortality, reduced milk yield and the expenses incurred for vaccination leads to severe economic loss.

Predisposing factors

pH of the infected soil, infected wool, materials, hides and other materials.

In wet soil, and in stagnant water spores are concentrated and suspended.

Alkaline soil (pH 9.0) under warm climate preserve the organism to develop anthrax but acid soil destroy the organism.

Blood transfusion may also spread the disease.

Contaminated bone meal, pasture contaminated with tannery effluents, fodders grown on infected soil, turning up of soil, blood and other discharges from infected animals are the major source of infection.

Calcium rich alluvial soil, organic and poorly drained soils have the risk of causing endemic infection.

Source of infection

Contaminated soil, environment, infected excretions and secretions from animals.

Transmission

Ingestion, inhalation and contamination of wound by spores are prime mode of spread.

Injury to oral mucosa permits the invasion of the organism.

Inhalation plays less important role in animals contrast to more spread in human being and is responsible for causing wool sorters disease.

Mechanical transmission through Tabanid fly bite occurs.

Host affected

Cattle and sheep are highly susceptible as compared to goat and horses.

Human is less susceptible than cattle.

Pigs, dogs and cats are relatively resistant.

But once affected the case fatality rate is high in farm animals and pigs.

Hippopotamus, cape buffalo and elephants die in large numbers due to anthrax.

Persons working in wool and hide industries are mostly affected.

Predators acts as carrier for this infection.

Pathogenesis

Discharges and materials containing anthrax bacilli when exposed to air, spores are produced.

The spores are very resistant in the external environment but the un-germinated spores are considered not harmful it become vegetative form inside the host.

The organism is resistant to phagocytosis due to the presence of poly D glutamic acid containing capsule, and triple toxin factors such as edema factor-I, lethal factor-II and protective antigen-III.

Primarily, spores proliferate in the regional draining lymphnodes, subsequently, travels via lymphatic vessels and reach the blood stream and cause septicemia followed by massive invasion into all body tissues.

The lethal toxin of B.anthracis causes edema, tissue damage, and death as a result of shock, acute renal failure and terminal anoxia. The blockage of capillaries initiating death is commonly known as "Log Jam" theory.

As per the evidence atleast 3x106 bacteria/ml blood is necessary for causing death.

In pigs, localiztion of the organism occurs in the lymphnode of the throat following invasion through upper part of the digestive tract eventually lead to a fatal septicaemia.

Shock acute renal failure and terminal anoxia leads to death.

Clinical Signs and Zoonosis

Cattle and sheep

Peracute form

Sudden death without any premonitory signs. Upon close observation following signs will be seen.

Fever, muscle tremor, dyspnoea, congestion of mucous membrane are noticed.

Animal collapses and die due to terminal convulsions.

After death, oozing of blood from nostrils, mouth, anus and vulva is noticed.

Acute form

Incubation period of the disease is 1-2 weeks.

The course of this form is about 48 hours.

Fever (42°C), severe depression, listlessness, congestion and heamorrhage of deep mucous membrane, increased heart rate and rapid respiration observed.

Affected cattle with mouth breathing due to oxygen hunger.

Abortion, decrease in milk yield, blood stained or deep yellow color milk, diarrhoea, local edema of the tongue, throat, sternum, perineum and flank occur.

Pigs

Acutely and sub-acutely infected animals show high temperature, appears dull, anorectic with distinct inflammatory edema in throat and face.

Painless swelling causes obstruction which leads to swallowing and respiration difficulty.

Blood stained froth present at the mouth.

Petechial hemorrahges of skin, dysentery without any edema of throat occurs.

Pulmonary form

In baby pigs, it develops lobar pneumonia and exudative pleuirisy through inhalation of dust which leads to death in a day or two.

Occassionally, affected individuals may be alive for several days after infection.

Horse

Always horses are affected with acute infection by ingestion and leads to septicaemia, enteritis and colic.

Painful, edematous and subcutaneous swellings appear in throat over the lower neck, floor of the thorax, abdomen, prepuce and mammary gland.

There is a high fever, severe depression, dyspnoea due to swelling of the throat or colic due to intestinal irritation.

The course of the disease is about 48-96hours.

Zoonosis

It is a fatal disease of human beings.

B.anthracis is an agent of bio-terrorism and listed as category A disease by OIE.

Occupational hazard by inhalation of spores occurs mostly while sorting out wool and processing of hides.

NECROPSY FINDINGS

Absence of rigor mortis with gaseous decomposition, quick assumption of the characteristic saw horse posture.

Un-clotted tarry colored blood oozes out through natural orifices.

There is a soft and enlarged spleen with a black berry jam consistency and is important feature of anthrax.

The carcass suspecious of anthrax should not be opened before confirmation made by peripheral blood smear examination.

In horses and pigs enlargement of local lymphnodes, lesions in the soft tissues of the neck and pharynx are important and it is called as pharyngeal form of anthrax.

Diagnosis

Based on clinical signs and necropsy findings.

Isolation and identification of organism.

Haematological and blood chemistry examinations should not be conducted because of the risk for human exposure.

The square ended blue bacilli (chain) with metachromatic pink capsule detected by microscopic examination after staining with ripened polychrome methylene blue stain is called as 'McFadyean's reaction'.

In early stages bacilli may not be present in blood, so, culture can be done or the materials like infected fluid can be injected into guinea pigs would give proper diagnostic result.

Fluorescent antibody technique using monoclonal antibody can be done to detect the disease.

In decomposed carcass vegetative bacilli may not be present, in such a condition diagnosis is difficult so that the protective antigen is detected by immuno-chromatography test. It has a high specificity but does not give positive results in recently vaccinated cattle.

Isolation of bacilli from infected soil is difficult but real time quantitative PCR and Nested PCR have been found highly sensitive.

In human cutaneous anthrax is diagnosed by Immunohistochemical detection of the bacilli in the skin biopsies.

Gelatin stab culture: The growth resembles an 'inverted fir tree appearance' with slow liquefaction commencing from the top.

Nutrient agar media: The 5% blood agar show 'medusa head colonies'

Ascolis test:To demonstrate the antigen in severely decayed carcass and the skin in which tube containing positive serum is overlayed with suspected sample develops a white precipitation ring at the junction of the two liquids.

Sample collection

Unopened carcass, blood, edema fluid in sealed leak proof containers and direct smear from tip of the ears.

In live animals, organism may be detected in a stained peripheral blood smear, edema fluid, lymphnode needle puncture smear, amputated tail or ears and jugular vein aspiration etc.

If anthrax is suspected then shipping of diagnostic samples via air or courier is not permitted.

Differential diagnosis

Lightening strike.

Peracute blackleg.

Malignant edema.

Bacillary hemoglobinuria.

Hypomagnesemia.

Treatment

Recovery occurs when the infection is identified in early stages and treated with penicillin 20,000 IU /kg bw twice daily for 3 days.

Streptomycin 8-10g/day in two divided doses IM for cattle is effective.

Oxytetracycline 5-10mg /kg/day IV or IM can be given.

Antiserum is given daily for 5 days however, it is expensive.

Prevention

Annual spore vaccine is recommended at endemic area. An uncapsulated, avirulent, glycerol added live spore containing strains of B.anthracis vaccine can be administered to all animals. However, glycerol suspended vaccine are not safe for small ruminants especially, in goats. Because, it may cause irritation, gangrenous edema, septicemia, and sloughing of tail at the site of injection (caudal fold). Montanide is an adjuvant added in vaccine is highly suitable for all ruminants including sheep and goats. It produces higher immunity.

Anthrax spore vaccine: It contains a 34F2 strains of B.anthracis, non-capsulated, avirulent (i.e. pX01+/pX02-), glycerol suspended spore vaccine. It can be used to protect all species of animals viz/- cattle, sheep, goats, horse, ass, elephant, pigs and camel. The vaccine is used both in disease free and in outbreak areas. Cattle, sheep and goats 1ml, in caudal fold, elephant and horses 1 ml, s/c followed by a booster 3ml, s/c one month following primary vaccination should be given.

The vaccine is used to protect all species of animals such as cattle, sheep, goats, horses, ass, elephants, pigs and camels respectively. The vaccine is used both in disease free and outbreak areas. Cattle, sheep and goats, elephant and horses 1ml each subcutaneously given. In elephant and horses it is advisable to give a second dose of 3ml after 1 month is advisable. The immunity following vaccination is established in about 10 days.

Following outbreak the animals can be consecutively vaccinated for three years for the prevention of further outbreak in the region.

Control

Anthrax suspected carcass should not be opened.

Plugging of natural orifices with cotton to prevent exposure and spore formation.

Carcass must be disposed by burning or deep burial.

Burial should be done in 2 meter deep with adequate application of quick lime, liberal application of 5% formaldehyde to control the spread of the spores.

h2 disinfection with 5% Lysol for 2 days, 5-10% solution of formalin or 2% sodium hydroxide is highly effective.

Peracetic acid 3% solution of 8L/m2 is considered as very good sporicide and effective sterilant.

Maintain suspected animals for 2 weeks under quarantine.

Vaccination of survivors, administration of hyperimmune serum to contact animals should be carried out.

Livestock and animal byproducts like meat, milk should not be taken out of the farm during quarantine period.


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