epidemiology concepts and ecology of disease

epidemiology

1. SUBMITTED TO: Dr.B .SRINU . MVSC,Ph.D. ASSISTANT PROFESSOR DEPARTMENT OF VETERINARY PUBLIC HEALTH AND EPIDEMIOLOGY Ecological Concepts Of Epidemiology And Natural history of diseases, Types of ecosystem,Landscape Epidemiology SUBMITTED BY : D.SNEHA wv/2022 - 10

2. What is ecology ?? The study of animals and plants in relation to their habits and habitation. In Greek oikos - house Logos - discussing It has two objectives : 1. An increase in understanding of the pathogenesis maintenance and Transmission of infectious agents of disease.

3. Natural history of diseases The natural history of a disease in a population sometimes called the disease’s ecology, refers to the course of the disease from its beginning to its final clinical end points. It encompasses several stages : Prepathogenesis Period : Before infection, when the disease agent simply exists in the environment. Incidence and Distribution : Factors affecting the. Diseases’s occurrence and distribution. Persistence or Disappearance : The disease may persist [endemic] or disappear in the environment.

4. Distribution Of the Population. Vegetational Zones Botanists were the first to note the division of earth into different vegetational zones. For example: Border between forest and tundra in northern regions, and zoning of forest as on ascends mountains. These apparent neat formations were first explained by de Candole who argued that climate particularly temperature dedicated vegetation. He draw the first vegetational map based isotherm. At the beginning of the 20 century Koppen used de Candolle’s classification on the basis of modern system provides a correlation between climatic vegetational zones

5. Regulation of population Size The Balance of Nature : Stability of animal and plant populations grow reach a certain size and stop growing. The population becomes stable and balanced with the rate of reproduction and equalling the death rate.

6. Control of Population Size by competition: Populations are brought into balance by competition for the resources of the habit. The most of which is food. Competition therefore is density-dependent. For example: Reproduction of Ascaris species is density -dependent. What is Dispersal ???? Process or result of spreading of Organisms from one place to another. DISPERSAL: In some parts of world there is a dramatic seasonal variations in climate.

7. In some parts of world , there may be dramatic seasonal variations in climate. An Australian species of grasshopper overwinters in its egg. The warmth of spring causes the eggs to hatch . The adults that develop then lay eggs as long as weather is wet . A drought kills all the adults . This is not density dependent; it occurs long before competition occurs. Such insects survive only by dispersal over large areas to different dimensions so that at least some are in the area that is wet. PREDATION: Predators has an obvious plausible role in controlling the size of populations , but most of the evidence suggest that this is not true for large animals because predators take only sick animals.

8. Predation could have some effect on population size. Predators have been used to control insect pests For example: Ladybirds to control cotton cushiony- scale insects . INFECTIOUS DISEASE: Infectious diseases are determining and regulating the size of population. For example : Rabbit hemorrhagic disease virus appears to be an effective method Of controlling. Rabbit population. Infectious agents can be divided into two groups according to their generation dynamics.

9. Microparasites Micro parasites multiply directly When inside the host, increasing the level of parasitism. Example:Virus, bacteria, protozoa Macroparasites Do not increase the level of parasitism: they grow inside the host, but multiply by producing Infective changes which are released from the host to infect. New hosts. Example:Helminthis and Arthopods

10. HOME RANGE: Certain animals have a natural restriction to the area over which they roam; this Home range. This may control the population, and has implications for the transmission of infectious diseases; infected animals may transmit infection over their home range but no further. For Example: Rats the maintenance hosts of the rickettsial disease scrub typhus.

11. TERRITORIALITY: The part of an animal’s home range that is defends aggressively from Invaders is the animal’s territory. This behavioural response is territoriality. Territoriality may also control the population because there is a minimum size to a territory and a finite amount of space, and therefore a finite number animals that can exist in territory. SOCIAL DOMINANCE: In the 1920s a social hierarchy called the ‘peck order’ was discovered among the birds. Some gregarious species, especially rodents, inhabit favourable places. When crowding occurs the socially weaker animals are forced out. This may be a population control mechanism.

12. THE NICHE Logistic equation for each species to find the relative size of each population produces pairs of equations that were derived independently in US by Loktla 1925 and in Italy by Volterra 1931. These equations are therefore called Lotka-Volterra equations. They can be derived for varied for degrees of competition. The conclusion drawn from these equations is of fundamental importance in ecology. It is that the coexistence of fundamental species is impossible. Coexistence is Possible if the competition is weak . This lead to the principle of competitive exclusion. That the competition will exclude all but one species from a particular position defined by an animal’s feeding habits, physiology, mechanical, habits and behaviour.

13. This position is ‘animal niche . The principle of competitive exclusion can be summarised As “ One species, One niche’’

14. Louse Infestation Lice tend to host specific. Pig lice do not live on man or dog or vice versa. By being Host specific, species of lice avoid competition, i.e, they have their own niche. Two types of lice on man; the head louse and the body louse each parasitising the two different parts of the body . Intracellular parasites occupy a niche in the cells They include all viruses, bacteria, and some protozoa. There are several advantages to this type of existence such As safety from humoral antibodies and extracellular agents. Some Examples Of Niche Relating to Disease

15. A Particularly biome contains different types of animals and plants.Some are Common, others are scarce. Some are large, others are small. Animal tend to move about en masse, and so it is difficult to study them all Simultaneously. FOOD CHAIN Charles Elton noted what foxes ate in the summer and winter. In summer the Foxes ate birds. The birds ate berries, tundra, leaves and insects. The insects also ate leaves. Thus Elton noted that there was a food chain : tundra-insects-birds-foxes. The Relationship between different types of animals and plants

16. In the winters there was a different food chain : marine animal-seal-polarbear dung-fox. In animal communities therefore, a complex system has evolved, with food chains Linking animals.

17. The Size Of Animals and Food Webs Elton Observed that animals fed at different levels in the foodchain. These levels He termed tropic levels. He also noted that animals occupying different tropic levels generally of different sizes. The foxes were the largest, and the birds were smaller.Similarly those further down the pyramids[ e.g the insects] were even smaller.

18. The Significance Of food web to disease transmission The food web of an animal can determine to which orally transmitted infectious agents an animal acts as host and from which food poisoning toxins it is at risk. Helminth diseases, for which there are definitive and intermediate hosts, are frequently transmitted via foodwebs. For example:The Tape worm Echinocoocus granulises includes sheep as an intermediate hosts, and the dogs as the definitive host. The cysts in liver and the lungs of intermediate hosts are transmitted to dogs when the latter eat sheep of fal; raw sheep offal should not be fed to dogs.

19. Salmon Poisoning: Rickettsia parasitises a fluke that in turn parasitizes a snail that in turn releases infected miracidia, which parasitises the salmon. Feeding Salmon to dogs transmits the rickettsia.

20. ECOSYSTEMS The relationship between animals linked by food chains defines the variety of animals in a particular area. Similarly, climate and vegetation govern the distribution of plants and therefore of the animals that live off them. These areas are characterised by the animals and plants that occupy them, and by their physical and climatic features. The unique interacting complex is called an ecosystem. Components of ecosystem Biotope It is the smallest spatial unit providing uniform conditions for life. Biocensis Biocensis is the collection of livingorgansims in a Biotope.

21. TYPES OF ECOSYSTEM Three Types of ecosystem according to their origin. 1. Autochthonous 2. Anthropurgic 3. Synanthropic Autochthonous : Autochthonous derives from the Greek Autos = “ oneself or itself” Chthonic = “the earth or the land’’

22. Autochthonous ecosystem is one coming from land itself. Example : Tropical rainforest deserts

23. Anthropurgic ecosystems Anthropurgic is derived from Greek Anthropos: man Rooterg : to work at to create to produce Anthropurgic ecosystem is one created by man Examples: Cultivated pastures and towns.

24. Synanthropic Ecosystems Synanthropic originates from the Greek Syn : along with,together with’ Anthropos : ‘man’ Synanthropic ecosystem is one that is in contact with man. Synanthropic ecosystems facilitate the transimision of Zoonotic infections from their lower animal hosts to man For Example : Rats inhabited in rubbish dumps infected with leptospira may be Source of infection to humans.

25. An Ecological Climax When plants, animals, microbes, soil, and microclimate have evolved to a stable, balanced relationship, an ecological climax traditionally is said to have occurred. When infectious are present, they too are stable and therefore are usually endemic. Also, the balance between host and parasite usually results in inapparent Infectious. Such stable situations can be disrupted frequently by man resulting in epidemics. Example: BlueTongue a viral disease of sheep, was present in indigenous sheep It is part of an ecological climax.

26. Ecological Interface An ecological interface is a junction of two ecosystems. Infectious diseases can be transmitted across the interfaces. Example Transmission of yellow fever, an arbovirus disease of man. The Virus is maintained in apes in Africa in autochthonous ecosystem in the forest. The mosquito, Aedes africans transmits the virus between apes. The mosquito Aedes Simpson, bridges the interface between the autochthonous forest ecosystem and the anthropurgic cultivated areas. The mosquito therefore maintaining a plantation cycle in which man and apes may be infected. Finally the urban mosquito Ades aegypti an urban cycle in man.

27. ECOLOGICAL MOSAICS An ecological mosaic is a modified patch of vegetation created by man, within a biome that has reached a climax. Infection may spread from wild animals to man in such circumstances. Example: Clearing of the forest encourages a close cover of weeds on the ground creating the conditions that are favourable for the incursion of field rats with the mites infected with scrub typhus which form mite islands and that local areas becomes endemic for scrub typhus.

28. LANDSCAPE EPIDEMIOLOGY The study of diseases in relation to the ecosystem in which they are found, is Landscape epidemiology. Terms such as medical ecology, horizontal epidemiology, and medical geography also convey the same meaning Landscape epidemiology was developed by Russian Pavlovsky and later expanded By Andy and Galuzo. NIDALITY: The Russian steppe biome was the home of the great plagues such as rinderpest.

29. Many Arthopods transmitted infectious present in the steppes were also limited to distinct geographical areas. These foci were natural homes of these disease and were called nidi. The presence of a nidus depends on its limitation to particular ecosystems. An area that has ecological, social and environmental conditions that can support a disease is a nosogenic territory. Greek : nose = sickness, disease; Gen = to produce, to create. A nosoarea is a nosogenic terrotority in which a particularly disease is present.

30. Objectives Of landscape epidemiology Landscape epidemiology is founded on the concept that if the nadality of diseases is based on ecological factors then a study of ecosystems enables predictions to be made about of occurrence disease and facilitates the development of appropriate control strategies. Example: Kyasanur forest disease. It is caused by an arbovirus. It is caused by an arbovirus . It is restricted to an area 600 miles square in Mysore. The virus endemically And inapparently infects some small mammals, including rats in the local rain Forest.