General Introduction: hunter/gatherers versus agriculturalists, The rise of agriculture contributed to the spread of disease. Tuberculosis and diarrheal disease arose with the advent of farming, measles and bubonic plague appeared with the advent of large cities, which were made possible by agricultural practices. Population densities of hunter-gatherers are rarely over one person per ten square miles, while farmers average 100 times that. This crowding facilitates the spreading of pathogenic diseases. The domestication of animals also facilitates easier spreading of diseases from animals to humans. Farmers also produce a few starch rich crops that are lacking in essential vitamins, minerals and amino acids, populations that rely on a lack of diverse foods have lower quality health. Skeletons from farmer societies also showed signs of anemia, tuberculosis, leprosy, enamel defects and other diseases tied to malnutrition. The average height of some societies also drastically decreased between the end of ice ages to the classical era.In the context of disease hunter gatherer societies are advantageous to agricultural societies as they practice a lifestyle of diverse diet that permits better nutrition, a low population density and domestic animal population that reduces the spread of parasites and infectious disease. predation and parasitism, Predation: Predation refers to the act of killing another animal for food.example, Lions eating zebras or zebras eating grass. Predators are well adapted to finding, overpowering and quickly killing prey. Example, a tigers strength, speed, camouflage and stalking behavior. Prey are well adapted at hiding, hindering and running from predators. For example, a caterpillar’s camouflage, torns and toxicity. A predator should also have immunity against poisons of a prey. Parasitism: refers to the act in which one organism lives in or on another organism as a parasite.Parasites grow, feed and shelter inside or upon a host organism, the relationship is harmful to the host organism. Though most parasites do not kill the host organism, some parasites may eventually kill the host. These parasites are pathogenic, causing diseases in the host. Ectoparasites such as lice, mosquitoes and fleas, protozoans such as amoeba and Plasmodium, and worms such as roundworm, tapeworm, and pinworm are parasitic in humans. Aphids and some insects are plant parasites drinking the sap. The parasites in the intestine of animals feed on partly digested food. Generally, parasites are smaller in size than the host organism. But, they exhibit higher reproduction rates once they invade the host. Some of the developmental stages of the parasitic life cycle occur inside the host. Predation and parasitism are two interspecific relationships that occur between two different species of an ecosystem. In predation, the predator immediately kills the prey while in parasitism, the parasite does not kill the host organism. Generally, a predator is large in size than the prey. On the other hand, a parasite is smaller than the host organism. The main difference between predation and parasitism is the type of relationship between the individuals of the two species. size of pathogens Flatworm animal length (maximum) 25 m Loa loa Loa loa length (female) 20-70 mm Tongue-eating louse length (female) 8-29 mm Pinworm 8-13 mm Head louse length 2.5-3 mm Tapeworm length (minimum) 1 mm Scabies length (female) Giardia length10-20 μm 0.3–0.45 mm Yeast infection diameter Lyme disease length10 μm Malaria 7-14 μm Plague lengtha few μm Tuberculosis 10-12 μm Yersinia length2-4 μm PlasmodiumMalaria diameter (asexual form) 1-2 μm Mycoplasma genitalium (one cause of urethritis) length600 nm HIV diameter 120 nm Orthomyxoviridae Influenza diameter Virus Rhinovirus Common cold Porcine circovirus diameter 50-120 nm 30 nm 17 nm Constructs of disease prior to ‘germ theory’ The miasma theory the predominant theory of disease transmission before the germ theory. It held that diseases such as cholera and the Black Death were caused by a miasma a noxious form of "bad air" emanating from rotting organic matter.Miasma was considered to be a poisonous vapor filled with particles from decomposed matter that was identifiable by a foul smell. The theory was that diseases were the product of environmental factors such as contaminated water, bad smelling air and poor hygiene. Infections were not passed between individuals but would affect those within a locale that gave rise to such vapors. Evil Eye and Witchcraft People often believed the existence of supernatural forces or spirits to explain events that do not have a clear biological or psychological explanation, a tendency that is especially acute for harmful events. In ancient times, people needed a theory for predicting, and from which they could attempt to control, the spread of disease. A belief in contagious and contaminating evil forces would have provided a functionally equivalent framework for prediction and management, identifying both the infection and transmission profile of pathogens. Some people also believed disease was caused by magic and witchcraft throughout history, a case in point is the escalation of witch-hunts in response to the Black Death. These incorrect assumptions affected overall health negatively in some cases as the case of witch trials or people congregating to pray, but positive in some cases as people practiced proper hygiene and worked towards removing rotting organic matter and sources of foul smells which may be indicative of harmful bacteria. Discussion of disease causing organisms, vectors and transmissions. Vector-borne diseases are human illnesses caused by parasites, viruses and bacteria that are transmitted by vectors. Such diseases include malaria, dengue, schistosomiasis, human African trypanosomiasis, leishmaniasis, Chagas disease, yellow fever, Japanese encephalitis and onchocerciasis. Vectors are living organisms that can transmit infectious pathogens between humans, or from animals to humans. Many of these vectors are bloodsucking insects, which ingest disease-producing microorganisms during a blood meal from an infected host (human or animal) and later transmit it into a new host, after the pathogen has replicated. Type 1, 2 and 3 epidemics Type 1 epidemic is a common source outbreak. These occur when the rise in cases of an infection occurs after a group of people all come into contact with the same unsafe source of infection (the common source), such as contaminated food or water. Example a village drinking from a well with water contaminated by a dead animal causes everyone in the village to fall ill. The infected water is the common source. Type 2 epidemic is a propagated or progressive epidemic. These occur when the infection spreads from person to person. The infectious agents causing the disease pass from one host to another, either directly from person to person, or indirectly via vectors, or another medium such as water. The distribution of malaria cases is a good example of a propagated epidemic, because increased numbers of malaria cases occur again and again at different times. A type 3 epidemic is a mixed epidemic. These show characteristics of both common source and propagated epidemics. So a mixed epidemic can start with a common source and be followed by a propagated spread. An example is an outbreak of typhoid fever from a common contaminated source such as a well polluted by feaces. The fever can then spread from person to person thus exhibiting characteristics of common source and propagated outbreak. Six plagues of the ancient world 1. Pharaoh's Plague A researcher in Egypt unearthed cat and human fleas ,known to be bubonic plague carriers in some cases, in and around the homes of an ancient Egyptian excavation site . Another clue that the Pharaoh's plague was the bubonic plague is that previous excavations along the Nile Delta had turned up Nile rats, an endemic species, dating to the 16th and 17th century B.C. The plague's main carrier flea is thought to be native to the Nile Valley and is known to be a Nile rat parasite.The Nile provided an ideal spot for rats to carry the plague into urban communities. Around 3500 B.C., people began to build cities next to the Nile. During floods, the habitat of the Nile rat was disturbed, sending the rodent and its fleas with the plague bacteria into the human settlements. 2. Plague of Athens The Plague of Athens was an epidemic that devastated the city-state of Athens in ancient Greece in 430 BC. The plague killed an estimated 75,000 to 100,000 people, around one quarter of the population, and is believed to have entered Athens through Piraeus, the city's port and sole source of food and supplies. It is believed that the epidemic was an outbreak of Typhus due to the consistency in the mortality rate and DNA evidence found in an ancient Greek burial pit. 3. Cyprian Plague The Plague of Cyprian was a pandemic that afflicted the Roman Empire about from AD 249 to 262. The agent of the plague is highly speculative because of sparse sourcing, but suspects have included smallpox, pandemic influenza, and viral hemorrhagic fever (filoviruses) like the Ebola virus. The plague is thought to have caused widespread manpower shortages for food production and the Roman army, severely weakening the empire 4. Roman Plague The Antonine Plague of 165 to 180 AD, also known as the Plague of Galen, was the first known pandemic impacting the Roman Empire, possibly contracted and spread by soldiers who were returning from campaigns in the Near East. Scholars generally believe the plague was smallpox 5. Plague of Justinian The Plague of Justinian or Justinianic Plague was the first major outbreak of the first plague pandemic. The disease afflicted the entire Mediterranean Basin, Europe, and the Near East, severely affecting the Sasanian Empire and the Byzantine Empire and especially its capital, Constantinople. In Constantinople it was killing 10,000 people a day at its height. Researchers confirmed earlier speculation that the cause of the Plague of Justinian was Yersinia pestis, the same bacterium responsible for the Black Death. The plague's long-term effects on European and Christian history were significant. As the disease spread to port cities, the struggling Goths were able to carry out successful campaigns against the Byzantines. The plague weakened the Byzantine Empire to a critical point, when Byzantine armies had nearly retaken all of Italy and reunited the core of the Western Roman Empire with the Eastern Roman Empire, the Lombards invaded Northern Italy, defeated the small Byzantine army that had been left behind and established the Kingdom of the Lombards which went on to become the kingdom of Italy. The Roman empire would remain split for the rest of history until their total defeat by Germanic tribes in the west and Turks in the east. Bubonic Plague Bubonic plague is an infection spread mostly to humans by infected fleas that travel on rodents. Called the Black Death, it killed millions of Europeans during the Middle Ages. Prevention includes reducing your exposure to mice, rats, squirrels and other animals that may be infected. There is no vaccine. The Justinian plague mentioned above was the first instance of the bubonic plague. Later on in the middle ages the infamous black death would emerge and become the deadliest disease outbreak in history.It killed one third of the European human population.Historians believe that society subsequently became more violent as the mass mortality rate cheapened life and thus increased warfare, crime, revolt, and persecution. Europe lost a majority of its doctors and many villages were left entirely abandoned.