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Public health is a branch of medical sciences that primarily deals with the surveillance, control, detection and prevention of the emergence and spread of infectious diseases in a defined human population. It involves the protection and improvement of the health of the general public. In clinical medicine, doctors and nurses practice their profession by looking at the health issues of individuals who turn out to be their patients, but in the practice of public health, the entire community and not individuals are regarded as patients. Public health professionals go beyond treating individuals when they fall sick or become injured (which is usually the main task of clinicians) to preventing infectious diseases and other health-related emergency from either occurring or re-occurring within a specific human population. It is the scientific discipline that promotes the health of the general public by preventing, detecting and controlling infectious diseases as they emerge. Public health is a field of the medical sciences that ensures improved quality of life for the general public by making sure that people imbibe good environmental sanitation and personal hygiene aside other relevant precautionary measures as sustainable means of restrain the emergence and spread of infectious diseases.

Infectious diseases are a leading cause of morbidity and mortality across the globe, and they have more ravaging effects in developing or low income countries where environmental sanitation, water supply, standard of living, medical care among other developmental factors are still poor. Infectious diseases including malaria, HIV/AIDS, cholera, Ebola virus, Lassa fever, multidrug resistant bacteria, hepatitis, gonorrhea, influenza, tuberculosis and food borne diseases impose colossal economic burden on the entire society. They can cripple the workforce of any nation if taken lightly, and thus timely detection and containment is paramount among all other factors. A well trained, prepared and proactive public health labor force is critical in any nation as a panacea to dealing with the threats of emerging and re-emerging infectious diseases.

Some key functions of public health personnel’s include the following:

  1. To protect the health of the entire community (including a village, local community/district or an entire nation).
  2. To improve the health status of an entire community through health education and promotion of personal and communal hygiene.
  3. To focus on the general populations rather than individuals in the research and development of preventive measures against contracting infectious diseases.
  4. To be proactive, and develop therapeutic and defensive measures against the emergence and spread of infectious diseases in the community.

The development and use of vaccines, antibiotics, and other antimicrobial agents in the fight against infectious agents (including bacteria, viruses and fungi) have significantly saved countless number of people from the fatality caused by infectious diseases. However efficacious and powerful these antimicrobial agents are, and however proactive the activities of public health specialists are in containing the menace of infectious diseases; infectious diseases cannot be completely eradicated from planet earth. This is due in part to the ingenuity of microorganisms (including viruses, protozoa, bacteria and fungi) in evolving new ways of overcoming the protective capacity of the body’s immune system. Secondly, microorganisms are constantly evolving and re-evolving, and many have even developed resistant to some available therapeutic measures.

Pathogenic microorganisms have become more sophisticated and can now survive even in the face of antimicrobial onslaught. Some have even developed mechanisms that allow them to remain undetected in vivo or use the body’s immune system to their own advantage. The entire population still remains at high risk of the menaces of infectious diseases, with the women, children, and the immunocompromised remaining the most vulnerable. New infectious diseases are emerging and even old ones which were taught to have been eradicated are now re-emerging and have remained obstinate in the human population. Irrespective of the sophistication of pathogenic microorganisms and their inventiveness in evading the body’s immune system and the action of antimicrobial onslaught, it still remains the duty of public health professionals to intervene in the cycle of infectious disease development and spread in the entire community. This can be made possible through improving available public health systems, encouraging environmental sanitation and safety, and also to develop sustainable measures of containing infectious diseases whenever and wherever they may occur. Since public health professional’s regards and look at the general population as its patient, it is vital that relevant health information’s are constantly made available to local communities, vulnerable groups, and the entire population on how to keep infectious organisms at bay, and on how to act when there is any disease outbreak in their locality.

The distribution of parasitic diseases which are of public concern are influenced by many factors including climatic changes, increased globalization and free movement/transport of people across the globe which allows pathogens to be moved from one geographical location to another. Public health microbiologists help to control the spread of communicable diseases including tropical and subtropical parasitic diseases through timely detection and reporting. They also monitor food establishments and water supplies in an attempt to keep them safe and free from infectious agents including microorganisms. In this book, parasitic diseases as it affects the many parts of the African continent and other parts of the tropic and subtropical regions including Asia and South America shall be expanded as a key public health issue in this book. The occurrence and widespread distribution of parasitic diseases across the tropical and subtropical countries of the world is a public health challenge of great importance confronting these regions, and which calls for concerted global efforts to assuage the malady.

Though some of these diseases (termed infectious diseases of poverty, IDP) are no longer a headache in most developed economies such as China, the USA, UK and the rest, the technological and medical advances in these nations coupled with their successes in other areas (the environment, water supply, and sanitation) which have long freed their regions from some of these diseases are also vital to the eradication of IDPs in the developing world, most especially in the African continent. However, it still rest on the shoulders of the African people themselves and other developing economies who are currently undergoing the menaces of IDPs (such as malaria, tuberculosis, schistosomiasis, leishmaniasis, filariasis and onchocerciasis) to come up with innovative ways of totally eradicating or bringing under control the IDPs in their regions since  a good chunk of these diseases (though still of global health importance) are no longer of great concern to the developed countries of the world who have in their own approach to things eradicated some of these diseases from their nations. The World Health Organization (WHO) in view of the fact that IDPs (though a problem of a specific region of the world) still portend a grave danger to the public health of everybody (developed or developing nations), has through the World Bank and its sister agencies started the Special Programme for Research and Training in Tropical Diseases (TDR) which has helped the developing countries (Africa in particular) with the technical know-how, resources, trainings and expertise directed at eradication or containing IDPs in the region. Most importantly, apart from providing research grants and other resources to tackle the diseases of poverty in the sub region, the TDR programme of WHO has also helped to develop and equip indigenous and skilled manpower (including scientists, researchers, academics, health professionals and the rest) who will harness local resources and technology to the effective containment of IDPs in their countries.

Parasitology is the study of parasites and their interaction with other organisms (i.e. their hosts). It is the study of parasites, their ecology, transmission and life cycle. The study of parasites is as ancient as mankind as man became conscious of his immediate environment. The field of Parasitology was fully established and widely appreciated in the early 1860’s. During this period, scientists as at the time postulated that protozoa and helminthes (which are both parasites) were actually responsible for some diseases of man and animals. Diseases and infections caused by parasites are by far amongst the top-most ever-present malady that man and his domestic animals encounter on almost daily basis aside bacterial, viral or fungal infections. The disease burden of parasitic infections cannot be over-emphasized, and this menace is experienced most in tropical developing countries where both natural and man-made activities has made it possible for the parasites to continue their devastating effects almost unperturbed. Though some bacteria, fungi and viruses are pathogenic, and cause disease and infections in humans; these microorganisms are not covered in the study of Parasitology even though they can coexist parasitically with man. Not all parasites are microorganisms (such flea and tick) but all microorganisms are parasitic in nature, and they cause harm or disease in their host. There are about 10,000 species of protozoal parasites with different life cycles, and that cause a variety of diseases in human beings and animals. Parasitic infections (example malaria) accounts for billions of resource waste in most parts of the world where they are a great source of concern and burden to health practitioners because they account to a colossal amount of mortality and morbidity in these regions (in the African and Asian continent where these organisms are most prevalent). Understanding the life cycles of these parasites and the mechanisms of their pathogenesis is critical to the containment of the diseases that they cause. There spread and transmission in any population can also be better controlled; and a reduction in economic wastages due to them will be achieved as well.

Parasites are living organisms that establish a physiological association with the tissues on the surface or inside the body of another organism called the host (example man, animal and host). The association between a parasite and a host is usually one that inflicts some level of injury and discomfort to the host, and this occasionally results to a disease or infection in the affected organism or host. This kind of association or relationship between a parasite and a host is called parasitism. In such relationships, only the parasites benefit while the host is often left diseased in the cause of the relationship. The host does not benefit but rather suffers the sole dependability of the parasite on it for food, water, shelter and protection. The host of a parasite can be definitive host, intermediate host or reservoir host.

Reservoir hosts store or harbour the parasite, and they serve as medium via which other susceptible human or animal hosts become infected by the protozoa. Definitive hosts are hosts that maintain the mature infective form of the parasite; and in some cases some clinically important parasites have humans as their only definitive hosts (example Trichinella spiralis). Sexual development of parasites takes place in the definitive host. Intermediate hosts are the second hostsof a parasite apart from the definitive host; and they are known to substitute with the definitive host and are usually known to harbour some reproductive stages of the parasite like the definitive host. Asexual development of parasites takes place in the intermediate host. In establishing a disease condition,parasites usually replicate intracellularly (i.e. inside the cells of its human host) as is seen in the Plasmodium species which solely multiply in the blood or extracellularly (outside the cells of its host) as is seen in Giardia species that develop in the lumen of the intestinal tract. There are a wide variety of parasites or protozoa that parasitize humans and cause diseases or parasitic infections; and some of these infections are subclinical in nature while the others are symptomatic and are presented with some clinical episodes that make the individual seek for medical help. The parasites that infect man and other animals are usually found all over the world and close to their immediate environments; and such organisms constitute one of the world’s greatest danger to the socioeconomic and wellbeing of humans.


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