Bacterial zoonosis- anthrax in animals and humans

this presentation deals with example of bacterial zoonotic disease like anthrax.

1. BACTERIAL ZOONOSES

2. ANTHRAX Synonyms : Woolsorter's disease (pneumonic anthrax or pulmonary anthrax), Rag-picker's disease, Knacker's disease, Hide-porter’s disease (cutaneous anthrax), Malignant edema, Malignant carbuncle, Malignant pustule, Charbon , Milz brand disease, Splenic fever Type of zoonosis : Direct anthropozoonosis ; Occupational zoonosis Definition: Anthrax ( ' Anthrakis '  is the Greek word, means 'coal', and referring to the blackened eschar skin lesion) is an acute infectious disease of all animals and human beings, caused by  Bacillus anthacis . Human infection is clinically characterized by necrotic cutaneous ulcer ( Eschar ), pulmonay manifestations and gastrointestinal manifestations, or some times meningeal form. 

3. In animals, anthrax is characterized by septicemia and sudden death, accompanied by the  exudation of tarry coloured unclotted blood from the natural orifices  (mouth, nose, ear, anus) and the important findings of  failure of the blood to clot, absence of rigor mortis  and bloaty appearance. Brief history: In 1876-1877, the absolute proof of the etiology of anthrax was established by  Robert Koch  and named it,  'Bacillus anthracis ' , and the famous  "Koch's postulates"  was formulated using anthrax as the model infection. In 1881, Louis Pasteur produced vaccine against anthrax. In 1939, Stern evolved a vaccine called  "Stern's vaccine / Spore vaccine"  and still used this technique for vaccine production for animals.

4. Etiology : It’s a Gram-positive , endospore -forming, rod-shaped (square-ended), non-motile and facultatively aerobic bacteria . There are two forms: (a). Vegetative form (capsular form) within the host and (b). Spore form in the environment, formed through sporulation , when exposed to oxygen in the air.   Spores are resistant against cold, heat, chemicals and drying. They are viable for many years (>60 years) in the soil (min.15 cm below) with neutral or alkaline pH and in alluvial soil ( cursed soil ). Acidic soil reduces the survivability of spores. Spores can be destroyed by heating at 100°C for 10 minutes , 5% NaOH , 10% formalin at 40°C for 15 minutes and 3% peracetic acid . Vegetative form can be killed at 60°C for 30 minutes. Spores used as one of a number of potential bioterrorism agents.

5. Reservoir and incidence It is distributed worldwide, except Antarctica. It is common in agricultural regions where it occurs in animas. Globally estimated annual cases are as many as 20000 to 100000 in humans. Many regions in India are still enzootic for animal anthrax and sporadic cases of human anthrax have been reported, especially from Tamil Nadu: Vellore, Vaniyambadi , Ambur , Sempattu ( Trichy ) and Chennai. Andhra Pradesh: Chittoor , Cuddapah , Gundur and  Prakasam . Telangana: Warangal, Khammam , Mahaboob nagar Karnataka: Mysore, Midnapore and Kolar .  Soil is the reservoir for the infectious agents. For man, the source of infection is always infected animals, contaminated animal products (leather, belts, wool, fur, hairs, skin and bone meal) or environmental contamination by anthrax spores.

6. Anthrax belt / Anthrax zone / Anthrax district:   It is determined by the soil type and climate, which is also termed as  "incubator area"  of anthrax. It is more common in tropical and subtropical countries than temperate countries. Outbreaks in animals often recorded when there is high rain fall after prolonged draught. The area will be enzootic for anthrax under these circumstances When the temperature is over 15°C with relative humidity of 60% and higher results in sporulation and soil-borne infection. This relationship to climate has made it possible to predict  "anthrax year" .  

7. Transmission: Herbivorous animals infected by ingestion of spores which are viable in soil for years and contaminated feed or water. Man is infected by Cutaneous route:  contact with contaminated carcasses, wool, hide or hair. Ingestion (Oral route):  ingestion of under-cooked infected meat. Inhalation (Respiratory route):   during wool sorting. It needs higher dose (LD 50 ) of 8000 to 10000 viable spores. Inhalation of spores along with ingestion of under-cooked infected meat is highly fatal than cutaneous route of infection. Mortality may be 20%, 25-60% and 100% respectively in cutaneous, oral and pulmonary route of infection.

8. Pathogenecity of anthrax bacilli depends on three factors, are Factor I:  Edema factor - Inflammatory property Fator II:  Protective antigen (PA) -  The capsular polypeptide, poly-D- glutamic acid , which is antiphagocytic in nature. It contains two plasmids px01 and px02 , which are responsible for the production of virulence factors. It produces three types of extracellular toxins and it is also an immunogenic factor. Factor III:  Lethal factor - Inflammatory property Disease in animals It primarily affects all warm-blooded animals, especially cattle, sheep, goats, horses and pigs.  Algerian sheep and dwarf pigs are naturally resistant to anthrax. It is also recorded in dogs , elephants, camels, tigers, cats, etc. The morbidity and mortality are 70 to 80 and 1 to 5% in highly susceptible and less susceptible animals, respectively.

9. Incubation period is 1-5 days. It occurs as peracute , acute, subacute and rarely chronic form. In swine, it is fatal, may be in pharyngeal form, intestinal form and septicemic form. Anthrax is characterized by septicemia and sudden death, accompanied by the exudation of tarry coloured unclotted blood from the natural orifices (mouth, nose, ear, anus) and the important findings of failure of the blood to clot, absence of rigor mortis and bloaty appearance . Carcass suspected for anthrax MUST NOT BE OPENED. In accidentally opened carcasses, splenomegaly (six time enlarged than the normal spleen) was observed, with  "black-berry jam consistency"  of spleen. 

10. Disease in man Cutaneous form (Malignant pustule, Hide porter's disease) Most common (95%) form of anthrax in humans. Incubation period ranges from 1 to 7 days . Then an erythematous papule appears on an exposed area of skin and becomes vesicular, with a purple to black centre . The center of the lesion finally forms a necrotic eschar and sloughs. Regional adenopathy , fever, malaise, headache, and nausea and vomiting may be present. After the eschar sloughs, haematogenous spread and sepsis may occur, resulting in shock, cyanosis, sweating and collapse . Haemorrhagic meningitis may also occur. Case fatality may be 20% if not treated.

11. Pulmonary form ( Woolsorter's disease) It occurs following the inhalation of spores from hides, bristles or wool. Incubation period ranges fro 1 to 5 days. It is characterized by fever, cough, dyspnea , respiratory failure and death in 24 hours. Case fatality may reach 100%. Intestinal form Less common form of anthrax. Incubation period ranges from 12 hours to 5 days. It is characterized by anorexia, vomiting and  diarrhoea . Case fatality may be 50% if untreated. Anthrax sepsis and anthrax meningitis can be developed in severe cases

12. Diagnosis: History of the patient and clinical symptoms. McFadyean's reaction:  Staining and identification of anthrax bacilli from the vesicular fluid or skin lesions, exudates of respiratory tract, blood by polychrome methylene blue staining or Giemsa's staining or Wright's staining.  Polychrome methylene blue staining with blood smear from ear vein (in suspected cases of anthrax in animals). Culture and identification: On nutrient agar with aerobic condition, it produces virulent or rough bacilli with  "medusa-head appearance" / "curled-hair appearance" / "bamboo-rod like appearance" / "spiked appearance" / "judge-wig appearance" On gelatin stab culture, it grows like  "inverted-fir tree"  ( becasue , it is facultatively anaerobic) Animal inoculation (in guinea pigs or mice). Ascoli's thermoprecipitation test  to detect antigen in the suspected materials.  PCR technique