Infectious diseases are majorly caused by bacteria, viruses, fungi or parasites. Many organisms live in and on our bodies. They're harmless or even helpful, but under certain conditions, few may cause disease. Some of the infectious diseases can be transmitted from person to person. Few are transmitted by insects or other animals and by consuming contaminated food or water or being exposed to organisms in the environment. Signs and symptoms vary depending on the organism and causing the infection, also include fever and fatigue. Mild infections respond to home remedies, while some life-threatening infections may need hospitalization. Infectious diseases such as measles and chickenpox can be prevented by vaccines.

COVID-19 infection leads to intestinal infection. Studies have cultured the COVID-19 virus from a single stool specimen. No reports of faecal−oral transmission of the COVID-19 virus have been found. Drug researchers realise the harmful effect a virus can have on people’s health and the entire world economy. Neglected tropical diseases are bacterial, viral, parasitic, fungal and non-communicable origin. NTDs share a common geographical and social context: their burden is predominantly located in tropical areas across the globe, and they majorly affect resource-poor communities and their correlation with the poverty is so close. The epidemiology of NTDs is complex and relates to environmental conditions.

Urinary schistosomiasis caused by trematodes of the genus Schistosoma known as Schistosoma haematobium. Schistosoma haematobium, also known to be “urinary blood fluke” that inhabits and multiplies eggs in the small venules of the perivesical and portal systems. Urinary schistosomiasis is endemic in 53 countries in Africa and the Middle East. A cholinesterase inhibitor Metrifonate is another selective treatment for SH; it has good efficacy and safety properties. Although it is economic, causes low recurrence rates. Metrifonate is that a prophylactic dose which is needed within two years to guard against recurrence. Niridazole is also highly effective for treating schistosomiasis, and a single dose of niridazole daily has a high cure rate.

Immunization is the method in which a person's system becomes fortified against the associative antigen. Once this technique is exposed to molecules that is foreign to the body, referred to as non-self, it'll orchestrate associate immune reaction, and it'll additionally develop the flexibility to quickly reply to a resultant encounter owing to immunologic memory. Therefore, by exposing associate to antigen in an exceedingly controlled manner, its body will learn to shield itself: this can be referred to as active immunization. The most necessary components of the system that can be improved by immunization square measure the T cells, B cells, and therefore, the antibodies B cells turn out. Memory B cells and memory T cells square measure chargeable for a swift response to a second encounter with a remote molecule. Passive immunization is the direct introduction of those components into the body, rather than the production of those components by the body itself.

Rickettsiae belong to the alpha-1 proteobacteria which are small gram-negative intracellular bacteria majorly transmitted by arthropods such as lice, fleas, ticks with two genera: Orientia with a unique specie and Rickettsia with several species. The clinical pictures which cause are known to be rickettsioses. All along the history, rickettsioses have been a threat and nowadays they are specifically cause of morbi-mortality in some areas of the world. Currently, ticks cause most travel-associated rickettsioses. Ticks are considered as one of the important vectors of infectious diseases in the world, preceded only by mosquitoes. Therefore, tick-borne rickettsioses are endemic all over the globe.

Ehrlichiosis caused by gram negative, obligately intracellular bacteria belonging to the genus Ehrlichia of the family Anaplasmataceae, Order Rickettsiales and the alpha sub-division Proteobacteria. Though they have a characteristic Gram negative cell wall structure, they lack the important enzymes to synthesize cell membrane components likewise lipopolysaccharide and peptidoglycan. As intracellular pathogens, Ehrlichia reside in cytoplasmic membrane-bound vacuoles inside host cells by forming microcolonies called morulae, which is derived from the Latin word “morus” for mulberry. Morulae range 1.0 to 6.0 µm in diameter which may contain uniform or mixed cell types.

Leptospirosis affects wildlife, domestic and man. Now a days, it is the highest incidence of zoonosis in the globe. It is considered as an occupational disease, and re-emerging infectious disease. Occurring of leptospirosis may be endemic and epidemic in developing countries with tropical and subtropical. Leptospirosis is caused by a spirochete Leptospiraceae family, consisting of two genera, Leptospira and Leptonema. The disease vary from common symptomatic infection in endemic regions, undifferentiated febrile illness, or syndrome to the presence of aseptic meningitis with low morbidity or similar to toxic shock syndrome with jaundice, myocarditis, renal failure and cardiac hemorrhage, meningitis and death have been described as epidemic in regions of severe leptospirosis in urban areas.

Bacteria of Bartonella are majorly hemotropic. They are gram-negative bacteria associated with erythrocytes and endothelial cells of mammals. Members within the genus bartonella have expanded during last three decades. Human pathogens B. bacilliformis, B. quintana and B. henselae, B. alsatica, B. elizabethae, B. grahamii, B. koehlerae, B. clarridgeiae, B. washoensis, B. vinsonii subsp. berkhoffii, B. vinsonii subsp. arupensis, B. tamiae, and B. rochalimae, have been described as human pathogens. A Bartonella infection causes fever that resolves quickly on its own to potentially fatal diseases with cardiovascular system. These shown the emerging medical importance of bartonellae.

Tuberculosis caused by Mycobacteria. Mycobacterium tuberculosis, also known as the Koch’s bacilli, which affects any organ or tissue in the body. This known to be a pulmonary disease, with their particular hallmarks such as occurrence of cough lasting more than 15 days, is the main corporal area affected. In such cases, individuals in such state are so-called respiratory symptomatic. Besides those signs, disease can be manifested with hemoptisis, fever, night sweating, general malaise, thoracic pain, anorexia and weight lost. This disease is still a significant public heal problem because of its high transmissibility and also it is highly potentially preventable and treatable condition.

The term dengue was derived from Spanish literature which was used to describe joint pain from an illness that attacked the British during the epidemic that affected the Spanish West Indies from 1927- 1928. Dengue was brought to the American continent during the colonization in the 18^th  century. Dengue virus symptoms are similar to those of several other infections, especially yellow fever. The etiology of dengue credited to an ultramicroscopic agent. Similarly, transmission has been considered through respiration and finally, by mosquitoes. Genetic variation was first demonstrated by serological techniques.