Epidemiology, prevention, and control of plague

Plague presentation

1. Department of preventive and social medicine Epidemiology, prevention, and control of plague

2. P lague A zoonoses Caused by Yersinia pestis , involving rodents and fleas Transmitted by infected flea bites to humans living or intruding into the same ecological environment Occurs in many forms- Enzootically Epizootically Sporadically In epidemics

3. Problem statement The data shows that from 2004 to 2009, 12503 cases of human plague, including 843 deaths were reported by 16 countries in Africa, A sia and America In 2004, I ndia reported a localised outbreak of bubonic plague in the D angud village district of Uttarkashi Fifteen people have been infected with bubonic  plague in 2015 in the United States, as told by the Centres for Disease Control and Prevention. Four of those cases were fatal.

4. Epidemiological determinants Agent factors A. agent Causative agent: Yersinia pestis , is a gram negative, non motile, coccobacillus, that exhibits bipolar staining. B acilli occur in great abundance in bubos , spleen, blood, liver, and other viscera of infected person and in sputum of pneumonic plague Plague bacilli can survive and multiply in soil of rodent burrows B . reservoir of infection Wild rodents are the natural reservoirs of plague In India, the wild rodent, Tatera indica has been incriminated as the main reservoir. C. Source of infection Infected rodents Fleas Cases of pneumonic plagues

5. Host factors A. age and sex All ages and both sexes are susceptible B. human activities Hunting, grazing, cultivation, harvesting and construction activities offer opportunities for flea-man contact C. Movement of people D. immunity Man has no natural immunity Immunity after recovery is relative

6. Environmental factors A. Season In northern India, the “plague season” starts from September to May. With the onset of hot weather, the disease tends to die out . In south India, there was no definite plague season Disease was found active all year round B. Temperature and humidity Temperature of 20-25 deg C and relative humidity of 60% and above are favourable C. Rainfall Heavy rainfall tends to flood the rat burrows. Responsible for keeping certain states free from plague. Eg , Bengal. D. Urban and rural areas E. Human dwellings

7. Vectors of plague Most common vector is the rat flea, X. cheopsis . Both sexes bite and transmit the disease Blocked flea A flea may ingest upto 0.5 cu mm of blood which may contain as many as 5000 plague bacilli. The bacilli multiply in the gut of rat flea and may block the proventriculus so that no food can pass through. Such a flea is called blocked flea

8. Flea indices useful in evaluating the effectiveness of a spray programme Total flea inex Cheopis index: more significant than total flea index. If >1, indicative of potential explosiveness of situation Specific %age of fleas Burrow index

9. Human plague Most frequently contracted from A. bite of infected flea B. direct contact with tissues of infected animal C. droplet infection from cases of pneumonic plague 3 types of human plague A. bubonic plague B. pneumonic plague C. Septicemic plague

10. Bubonic Plague Most common type Infected rat flea usually bite on lower extremities Bacilli proliferate in the regional lymph glands Typical features- Sudden fever, chills, headache, prostration Painful lymphadenitis Bubonic plague cannot spread from person to person because bacilli are locked up in buboes

11. Pneumonic Plague Primary pneumonic plague is rare Generally follows as a complication of bubonic septicaemic plague Septicaemic Plague Primary septicemic plague is rare, except for accidental lab infections

12. Prevention and Control Control of cases a. Early diagnosis: during epidemic situations, diagnosis can be made on clinical grounds In other situation, “rat falls” provide a useful warning of possible outbreaks Plague suspected humans and rodents must be examined bacteriologically to confirm the presence of plague. b. Notification: Case notification is required by international health regulations. c. Isolation d . T reatment: Drug of choice is Streptomycin – 30mg/kg body weight daily i.m . in 2 divided doses for 7 to 10 days Tetracycline, orally, 30-40mg of body weight daily in an alternative drug and sometimes given in combination with streptomycin Gentamycin, 2mg/kg of body weight loading dose, then 1.7mg/kg body weight every 8 hours i.v Sulphonamides, used if other drugs are not available e. Disinfection

13. 2. Control of fleas Most effective method to break the chain of transmission is destruction of rat fleas by insecticides DDT(10%) and BHC(3%), used as dust In areas of resistance to one or both of these, dust of carbaryl (2%) or malathion(5%) is used.

14. 3. Control of rodents Continuous mass destruction of rodents is an important plague preventive measure 4. Vaccination To be effective, vaccination should be carried out at least a week before an anticipated outbreak and the vaccine should be given in 2 doses

15. Chemoprophylaxis Highly recommended Should be offered to all plague contacts, medical, nursing, and public health personnel exposed to the risk of infection Drug of choice is tetracycline For adult dose is 500mg, 6 hourly for 5 days Cheaper alternative is sulphonamide, 2-3g daily for 5-7 days

16. Surveillance In areas where natural plague foci exist, or where there is history of past infection, surveillance is essential. Health education Emphasis must be placed on the need for the prompt reporting of dead rats and suspected human cases Medical practitioners should keep plague in mind for differential diagnosis of any cases of fever with lymphadenopathy, or when multiple cases of pneumonia occur

17. References: Park’s textbook of preventive and social medicine

18. Thank you