The lymph nodes are small, round or ovoid bodies placed along the
course of lymphatic vessels. They are surrounded by a fibrous capsule from
which trabeculae penetrate into the nodes. The node can be differentiated
into an outer cortex and an inner medulla. In the cortex are accumulations
of lymphocytes (primary follicles) within which germinal centers (secondary
follicles) develop during antigenic stimulation.
The follicles contain, besides proliferating lymphocytes, dendritic macrophages which capture and process the antigen. In the medulla, the lymphocytes are arranged as elongated branching bands (medullary cords). The cortical follicles and medullary cords contain B lymphocytes and constitute the bursa or bone marrow dependent areas.
Between the cortical follicles and medullary cords, there is a broad, intermediate zone called paracortical area which contains T lymphocytes and constitutes the thymus dependent area.
Lymph nodes act as a filter for the lymph. Each group of nodes drain
a specific part of the body. They phagocytose foreign materials including
microorganisms. They help the proliferation and circulation of T and B cells.
They enlarge following local antigenic stimulation. In the human body, totally
about 600 lymph nodes are distributed.
B. Spleen :
It is the largest lymphoid organ. It contains red and white pulp regions
that serve as filters. The macrophages within the spleen help to remove
and destroy pathogens.
Functions of Spleen :
1. The spleen serves as the graveyard for effete(aged) red blood cells, 2. It
acts as a reserve tank and setting bed for blood and 3. It acts as a systemic
filter for trapping circulating blood borne foreign particles. (The
immunological function of the spleen is primarily directed against blood borne
antigens).
The lymphoid system consists of the lymphoid cells (lymphocytes
and plasma cells) and lymphoid organs. Based on different roles they
perform, lymphoid organs can be classified into central (primary) and
peripheral (secondary) lymphoid organs. The central lymphoid organs are
lymphoepithelial structures in which the precursor lymphocytes proliferate,
develop and acquire immunological capability. In mammals, the bone
marrow, the thymus and the bursa of fabricius in birds represent primary
lymphoid organs. (Structure and Functions of the Immune System)
After acquiring immunocompetence, the lymphocytes migrate along blood and lymph streams, accumulate in the peripheral lymphoid organs and, following antigenic stimulus, effect the appropriate immune response. The spleen, lymph nodes and mucosa – associated lymphoid tissue (MALT) constitute the major peripheral or secondary lymphoid organs. Lymphoidal tissues in the gut ( peyer’s patches), appendix, tonsils, salivary glands, tear glands and also the secretion
(colostrums) of the lactating breast of the mother also are included in the
immune sysytem. (Structure and Functions of the Immune System)
Primary Lymphoid Organ
Thymus :
The thymus develops at about the sixth week of gestation. By eighth
week, it grows into a compact epithelial structure. Mesenchymal stem cells
(precursors of lymphocytes) from the yolk sac, foetal liver and bone marrow
reach the thymus and differentiate into the thymic lymphoid cells (thymocytes).
The thymus acquires its characteristic lymphoid appearance by the
third month of gestation. It is thus the first organ in all animal species to become predominantly lymphoid. In human beings, the thymus reaches its
maximal size just prior to birth. Thymus continues to grow till about the 12th
year. After puberty, it undergoes spontaneous progressive involution,
indicating that it functions best only in early life. (Structure and Functions of the Immune System)
The thymus is located just behind the upper part of the heart. It has
two lobes surrounded by a fibrous capsule. Septa arising from the capsule
divide the gland into lobules which are differentiated into an outer cortex
and an inner medulla. The cortex is crowded with actively proliferating
small lymphocytes. The medulla consists mainly of epithelial cells and mature
lymphocytes amidst which are the hassall’s corpuscles, which are whorl-like
aggregations of epithelial cells. (Structure and Functions of the Immune System)
The thymus was considered as an organ without any recognized
function. But its role in the development of cell mediated immunity has been
found recently. The primary function of the thymus is the production of
thymic lymphocytes(T cells). It is the major site for T lymphocyte
proliferation in the body. (Structure and Functions of the Immune System)
However, of the lymphocytes produced, only about one per cent leave the thymus. The rest are destroyed locally by programmed cell death or apoptosis. In the thymus, the lymphocytes acquire new surface antigens (Thy antigens). Lymphocytes produced in the thymus are called ‘thymus (T) dependent lymphocytes’ or ‘T cells’. Unlike, lymphocytes proliferation in the peripheral organs, the function of thymus is independent of antigenic stimulation. (Structure and Functions of the Immune System)
The thymus confers immunological competence on the lymphocytes
during their stay in the organ. Prethymic lymphocytes are not
immunocompetent. In the thymus they are ‘educated’ so that they become
capable of mounting cell mediated immune response against appropriate
antigens. This is effected by hormone-like factors produced by the thymus
such as thymulin, thymosin and thymopoietin. (Structure and Functions of the Immune System)
The importance of thymus in lymphocyte proliferation and development of CMI is evident from the effects of lymphopenia, and in neonatally thymectomised mice.
T lymphocytes are selectively seeded into certain sites in the peripheral lymphatic tissues. These are found in the white pulp of the spleen, around the periarteriole region, and in the paracortical areas of lymph nodes. (Structure and Functions of the Immune System)
Acquired immunity, also known as adaptive or specific immunity, is
capable of recognizing and selectively eliminating specific microorganisms.
Acquired immunity is found only in verterbrates. It supplements the
protection provided by innate/natural immunity. It is generated in response
to an exposure or encounter to the microorganisms in question. Specific
defence mechanisms require several days to be activated, following the
failure of non-specific defence mechanisms.
Unique features of the Adaptive immunity
(i) Specificity : It is the ability to distinguish differences among various
foreign molecules.
(ii) Diversity : It can recognize a vast variety of foreign molecules.
(iii) Discrimination between Self and Non-self : It is able to recognize and
respond to molecules that are foreign (non-self) to the body. At the same
time, it can avoid response to those molecules that are present within the
body (self antigens) of the given animal. (Acquired immunity)
(iv) Memory : When the immune system encounters a specific foreign agent,
e.g., microbe, for the first time, it generates an immune response and
eliminates the invader. The immune system retains the memory of this
encounter for a prolonged interval. As a result, a second encounter with the
same microbe evokes a heightened immune response.
Specific immunity employs two major groups of cells
(a) lymphocytes, and (b) antigen presenting cells. A healthy individual
possesses about a trillion of lymphocytes. The lymphocytes are of two types
viz., T- lymphocytes or T-cells and B – lymphocytes or B – cells. Both
the types of lymphocytes, as well as the other cells of the immune response,
are produced in bone marrow.
The process of their production is called haematopoiesis. Some immature lymphocytes, destined to become thymocytes, migrate via blood to the thymus, where they mature and differentiate as T – cells. The B- cells, on the other hand, mature in the bone marrow itself.
The B and T cells, together, generate two types of specific immunity, viz., (a) cell-mediated and (b) antibody-mediated or humoral immunity respectively. (Acquired immunity)
(a) Cell-mediated Immunity (CMI)
Cell-mediated immunity is the responsibility of a subgroup of T cells,
called cytotoxic T lymphocytes (CTLs). An activated cytotoxic lymphocyte
is specific to a target cell, which has been infected, and kill the target cell by
a variety of mechanisms. This prevents the completion of life cycle of the
pathogen and its growth, since it depends on an intact host cell to do that.
Cell-mediated immunity is also involved in killing of cancer cells. (Acquired immunity)
(b) Antibody-mediated Immunity / Humoral Immunity
Antibody mediated or humoural immunity involves the synthesis of
specific antibody molecules called immunoglobulins by the B-lymphtocytes.
Each antigen has many different antigenic determinants, each of which
matches a specific antibody and binds to it. The B cells, direct the antibodymediated immunity. The antibody molecules (Igs) may be bound to a cell
membrane in the form of receptors or they may remain free.
The free antibodies have three main functions viz.,
1. agglutination of particulate matter, including bacteria and viruses,
2. opsonisation or coating over bacteria to facilitate recognition and phagocytosis by the phagocytes and
3. neutralization of toxins released by bacteria. (Acquired immunity)
Adaptive immunity may be active or passive. Active immunity is
due to the immune response generated in the individual in question by a
pathogen or vaccine, whereas passive immunity is conferred by transfer
of immune products, like antibodies, etc., from an individual into a nonimmune
individual. (Acquired immunity)
Activation of Adaptive Immunity
Every antigen is processed by antigen presenting cells(APC), like
macrophages, B lymphocytes and dentric cells. The processed antigen is
presented on the surface of these cells.
A subgroup of T cells called T helper cells, specifically interacts with the presented antigen and becomes activated.
The activated T helper cells then activate B cells, and a subgroup
of T cells called cytotoxic lymphocytes (CTLs), in a specific manner. The
activated B and cytotoxic lymphocytes proliferate to produce clones. All the
cells of a clone can recognize the same antigen and eliminate it. (Acquired immunity)
Animals and human beings are continually exposed to various
infectious agents like bacteria, viruses, fungi and parasites. It has long been
noticed that survivors of certain diseases, e.g., measles, are not attacked by
the same disease again. Clearly, these people have become immune to the
concerned disease.
The system of animal body, which protects it from various infectious agents and cancer, is called Immune system. A study of the immune system is known as Immunology. This chapter introduces the fundamental concepts of immune system and their use for the improvement of human health and welfare.
The Latin term “Immunis”, meaning “exempt” or “freedom”, gave
rise to the English word immunity. It refers to all the mechanisms used by the
body for protection from environmental agents that are foreign to the body.
These agents may be microorganisms or their products, certain food items,
chemicals, drugs and pollen grains. Immunity is of two types : (a) innate, and
(b) acquired immunity.
A. Innate Immunity (Non-specific):
Innate immunity comprises all those natural defense mechanisms with which an organism is protected from infection. As a strategy, innate immunity consists of various types of barriers that prevent entry of foreign agents into the body. The pathogens that enter into the body, are quickly killed by some components of the immune system. This is the first line of defence in most animals. Innate immunity consists of the following four types of barriers. (IMMUNOLOGY)
1. Anatomical Barriers :
These barriers block the entry of organisms into
the body. The skin and the mucous membrane lining the respiratory and
intestinal as well as the reproductive passages constitute the barriers.
Mucous material entraps foreign microorganisms. The ciliary movements
produced by the epithelial lining cells expel out micro-organisms from the body.
2. Physiological Barriers :
Factors like body temperature, pH and various
body secretions, prevent the growth of pathogenic micro-organisms. For
example, fever response inhibits growth of many pathogens. Acidity of the
stomach contents due to HCl secretion kills ingested micro-organisms.
Lysozyme present in secretions, such as tears and saliva, digest bacterial
cell walls. Certain cells, like WBC, when infected with a virus, respond by
releasing anti viral proteins, called interferons. Interferons, in turn, make
the cells in the vicinity resistant to viral infections. As a result, the concerned
persons exhibit increased resistance to viral infections. (IMMUNOLOGY)
3. Phagocytic Barriers :
Phagocytosis is an important mechanism of innate
immunity. It is performed by leucocytes. In response to pathogenic
infections, the total count of leucocytes will increase sharply. Humans
contain wandering phagocytes that circulate throughout the body. The most
important phagocytes are the macrophages and the neutrophils.
Macrophages are large irregular-shaped cells that engulf microbes, viruses
and cellular debris. In response to an infection, monocytes are liberated at the site of infection. These monocytes get converted into macrophages. These
cells are provided with bacteriolytic enzymes and free radicals, which
destroy the pathogens. (IMMUNOLOGY)
4. Inflammatory Barriers :
Usually an infection or tissue injury results in
redness and swelling, along with pain and production of heat that may result
in fever. The above phenomenon is known as inflammatory response. This
response occurs due to release of chemical alarm signals, notably
histamine, serotonin and prostaglandins, by the damaged mast cells.
At the site of inflammation there may be leakage of vascular fluid, which
contains serum proteins with antibacterial activity. Further, there is an influx
of phagocytic cells into the affected area. These responses inhibit and
destroy the invading microorganisms. (IMMUNOLOGY)
Besides the phagocytes, natural killer cells (NK cells) (T Lymphocytes) kill virus-infected cells and some tumour cells of the body by creating perforin-lined pores in the plasma membrane of the target cells. These pores allow entry of water into the target cell, which then swells and bursts.
The disease Acquired Immuno Deficiency Syndrome (AIDS) was
identified in the year 1981 (December). Early epidemiological studies have
established that it is a communicable disease transmitted through sexual
contact or through blood and blood products.
In 1983 Luc Montagnier at Pasteur Institute, Paris and Gallo at National Institute of Health (NIH) USA isolated the virus that caused AIDS. In 1986, the committee on taxonomy of virus coined the term HIV or Human Immunodeficiency Virus
to avoid confusion due to different names being given by different reasearchers.
HIV is new member of the Lentivirinae subfamily of human
retroviruses. Retroviruses are RNA viruses, which have the capacity to
convert their RNA into DNA with the help of an enzyme called reverse
transcriptase.
Structure of HIV
HIV is spherical in shape. Its size is about 100-140 nm. Like any
other virus, it is made up of a central icosahedral capsid core containing the
genetic material surrounded by a protein envelope. The protein envelope is
attached several spicules of glycoprotein, Like other retroviruses the
glycoprotein sticks out on both sides (inside and outside) of its protein coat.
The outer position of glycoprotein called gp120 is attached to the gp 41
situated on the inner side of the viral coat. gp 41 is an unusually long protein
with over 100 amino acids. gp 120 appears like a knob. Electron
microscopic studies have revealed that the distribution of proteins of the viral
surface is very much like a soccer ball made of 12 pentagons and 20
hexagons, stitched together to make a sphere. The envelope of HIV also
contains other proteins including some HLA antigens (Human Leucocyte
Antigen).
The genome of HIV contains two helix of RNA molecules in folded
form. The enzyme reverse transcriptase is attached to RNA.
Pathogenesis
HIV causes profound immunodepression in humans. It is due to the
depletion of one type of WBC, which is involved in the formation of
antibodies called CD4 plus T-helper cells (lymphocytes). In addition other cells such as B-lymphocytes and macrophages are destroyed by HIV
infection. The infected macrophages serve as the reservoir of viruses and
dissiminate to all tissues in the body. HIV is found besides blood, in all body
fluids such as semen, vaginal secretion, cervical secretion, breast milk, CSF,
synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid and amniotic
fluid. HIV can even destroy the brain cells.
Symptoms
The following symptoms have been defined by WHO.
1. Weight loss at least 10% body weight
2. Chronic diarrhoea for more than a month
3. Prolonged fever for more than one month
4. Night sweats and persistent coughs
5. Opportunistic infections such as tuberculosis, oropharyngeal
candidiasis (fungal infection in mouth and throat)
6. recurrent herpes zoster (viral) infection
7. Meningitis and nerve damage
8. Loss of memory and intelligence
9. An unusual cancer, kaposis sarcoma which produces scattered
purplish lesions over the chest and abdomen.
Diagnosis
ELISA test (Enzyme Linked Immuno Sorbent Assay) is a sensitive
preliminary blood test used to detect HIV antibodies.
Western Blot is the confirmatory test, which is highly specific and
based on specific antibodies to viral core proteins.
Control and Management
1. Screening of blood and blood products.
2. Education to people about do’s and don’ts in AIDS contraction and
bringing more awareness among the public.
3. Education about protected sexual behaviour and practices
4. Participation of voluntary agencies, teachers, NGOs, paramedical
workers, several other voluntary health organizations, in AIDS awareness
programmes
5. Making the antiretroviral drugs such as AZTs (Azidothymidine/Zidovudin)
and saquinovir etc., available to patients.
The management of HIV infection involves the above general
measures, treatment of opportunistic infections and cancer, antiretroviral
drugs, immunomodulators and supportive treatment and counselling.
Antibiotics are special and unique type of chemotherapeutics agents
obtained from living organisms such as bacteria or fungi. The word antibiotic
refers to a metabolic product of one microorganism that in very small amounts
is detrimental or inhibitory to other microorganisms.
Antibiotics are special and unique type of chemotherapeutics agents
obtained from living organisms such as bacteria or fungi. The word antibiotic
refers to a metabolic product of one microorganism that in very small amounts
is detrimental or inhibitory to other microorganisms.
The first antibiotic that was discovered was Penicillin from the fungus, Pencillium sp. by Alexander Flemming in 1929. Since then hundreds of antibiotic substances have been isolated.
Antibiotics are of two types. 1. Broad spectrum antibiotics can
destroy or inhibit many different species of pathogens. 2. Narrow spectrum
antibiotics can destroy specifically some or few species of pathogens.
The mode of action of antibiotics may be either bactericidal or
bacteriostatic. The former destroys the microbial cells while the latter
inhibits the growth of them. Moreover, the antibiotics may inhibit cell wall
synthesis or disrupt the cell wall or damage the cytoplasmic membrane or
inhibit the protein synthesis and nucleic acid synthesis (purine and
pyrimidines); inhibit the specific enzyme systems and also inhibit the
metabolic pathway of pathogens through competitive inhibition of key
enzymes.
Some notable antibiotics are Ampicillin, Streptomycin, Tetracyclin
and Erythromycin etc. Some antifungal antibiotics are Griseofulvin and
Imidazole etc. Some antiviral antibiotics are Amantidine and Cycloguanosine.
The more promising chemotherapeutic agent for treating viral diseases is the
Interferon. Interferons are glycoprotein molecules secreted by the leucocytes
and fibroblasts. Some of the antitumour antibiotics are of the anthromycin
group.
Pathogenic microbes are provided with their own mechanisms to
establish infection in the host animals and humans. Similarly the hosts body
has a number of defense mechanisms to mount resistance against the
invasion and to prevent infection of pathogens. The antimicrobial response
of hosts may be natural, non-specific and specific.
Natural resistance includes species resistance, racial resistance and
individual resistance. (Antimicrobial Resistance)
Chemotherapy
The control and treatment of infectious diseases with a chemical
compound or drug is called chemotherapy. The chemical compounds and
drugs are called chemotherapeutic agents.
A good chemotherapeutic agent posses the following characteristics:
1. It destroys or prevents the activity of a disease causing pathogen, without
injuring the host tissues
2. It is able to penetrate the cells and tissues of the host and can encounter
the pathogens in effective but safe concentrations or dosage.
3. It leaves the hosts natural defense or immune mechanisms such as
phagocytosis or antibody production, unaffected.
4. It exhibits selective toxicity, that is it kills or inhibits the pathogenic
microbes without having harmful effect or having least harm to the host. (Antimicrobial Resistance)
Pathogenecity refers to the ability of microorganism to cause the
disease in animals and humans. Infectious diseases more often result due to
the interactions between the disease producing pathogenic microorganisms
and host organisms.
The Pathogenic adaptations
The Pathogenecity of the microbes is due to several phenomena or
adaptations.
1. Pathogens are able to selectively attach to the external surfaces such as
the skin and conjunctiva or the internal surfaces such as the mucus
membranes of the respiratory, gastrointestinal or urinogenital tracts.
2. They also penetrate the above body surfaces and gain access to the
internal tissues.
3. In some infections, the pathogen may remain localized, growing near its
point of entry into the body.
4. Some pathogens become widely distributed in different tissues or organs.
This is called generalized infections.
5. Some other pathogens can grow within the cells of host, causing severe
disturbances to normal physiological processes.
6. Yet another group, may grow extracellularly and bring damage to the body
tissues by elaborating substances called toxins. (Pathogenecity)
The pathogenecity differs in different strains of pathogenic species.
Some strains are highly virulent. In the case of virulent strains, only a few
bacterial cells may suffice to cause disease in a host. On the contrary, other
strains may be less virulent, and large numbers of cells may be needed to
cause the disease. Some strains may be avirulent, and are incapable of
causing the disease even when large numbers of cells are inoculated into the
host. Such avirulent strains are called attenuated strains. These are widely
used as vaccines to elicit the immunity.
Protozoans are eukaryotic, single celled organisms, which are
predominantly microscopic in size. The majority are between 5 to 250
microns in diameter. Protozoan microbiology is mostly concerned with the
disease aspects in humans. Some well known protozoan diseases in human
beings are the intestinal amoebiasis, African sleeping sickness, and malaria.
Several flagellate protozoans are responsible for diseases in both children
and adults. Giardia intestinalis is associated with diarrhoea in children.
Trichomonads are found in the mouth and cause gingivitis.
A. Plasmodium and Malaria (Protozoan microbiology)
Malaria is a mosquito borne disease caused by the protozoan,
Plasmodium. The life cycle of malarial parasite comprises two phases namely
the asexual phase in man and the sexual phase in the female Anopheles
mosquito (Definitive host).
Four different types of Malaria are recognized on the basis of period
of recurrence of fever. They are 1. Tertian, Benign Tertian or Vivax malaria,
caused by Plasmodium vivax. 2. Quartan Malaria caused by Plasmodium
malariae 3. Mild Tertian or Ovale Malaria caused by Plasmodium ovale
4. Malignant Tertian or Pernicious Malaria caused by Plasmodium
falciparum Of the four, the malignant type is fatal.
In malarial fever, the patient suffers from shaking chills, and
sweating. As the chills subside, the body temperature may rise to 106 o F.
The high fever is induced by the toxic haemozoin granules, which are liberated in plasma when the parasite schizonts burst out from the RBCS.
The patient also suffers from severe anaemia due to destruction of
erythrocytes. Other symptoms are enlargement of spleen, due to massive
increase in the number of phagocytic cells of the lymphoid macrophage
system.
In the case of falciparum infection thrombosis of visceral capillaries
occurs. Death takes place when the capillaries of brain are plugged with
both the parasites and the malarial pigment. Another very serious outcome
of the falciparum infection is black water fever. It is characterized by the
wholesome destruction of patient’s erythrocytes and the excretion of
liberated haemoglobin in the urine.
B. Amoebiasis (Protozoan microbiology)
Amoebiasis in man is due to the infection by the protozoan endoparasite
(Sarcodina) Entamoeba histolytica. It is worldwide in distribution but,
its prevalence is greater in tropics and sub tropics than in temperate zones.
The vegetative trophozoite form is pathogenic. The trophozoites make their
way deep into the sub mucosa of the large intestinal wall by eating through
the intestinal mucosa. The blood and the ulcer contents pour into the lumen
of the intestine and pass out as bloody stool. This characterizes the amoebic
dysentry or amoebiasis.
C. Other pathogenic protozoans (Protozoan microbiology)
Larval microbiology deals with human diseases caused by parasitic
larvae. Parasitic infections which man acquires from animals are known as
zoonotic infections or zoonoses. In the zoonoses, human infections are only
accidental events and the parasite is not benefited since the chain of
transmission is usually broken with human infection. The term anthroponoses
means infections with parasites species that are maintained in man alone.
Malaria and filaria are examples. The term Zooanthroponoses refers to
infections in which man is not merely an incidental host but an essential link in
the life cycle of the parasite (eg., Beef and pork tapeworm).
A. Salmonella and Human Diseases: (bacterial diseases)
Salmonella are pathogenic bacilli which cause three kinds of
infection to humans viz., enteric fever (Typhoid or Paratyphoid),
Gastroenteritis and Septicemia.
Typhoid fever is caused by S.typhi. It is transmitted via Pathogen
contained food and water. The disease is characterized by a continued fever, inflammation of the intestine, formation of intestinal ulcers and
enlargement of the spleen.
Gastroenteritis is caused by Salmonella, but most commonly by
S.choleraesuis. The bacteria reach the blood stream from the intestinal tract,
where it multiplies. It causes recurring high fever, chills, loss of appetite and
weight loss. When the bacteria infect the organs from blood they can cause
meningitis, pneumonia, abscesses, nephritis, osteomyelitis, or endocarditis,
etc.
B. Cholera : (bacterial diseases)
Cholera is caused by Vibrio cholere. It is a disease of antiquity and
has been the cause of untold sufferings and death. Cholera is transmitted in
water and food contaminated with this bacteria. In the small intestine, the
bacteria adhere to epithelium, multiply and produce the enterotoxin. The
symptoms of cholera are vomiting, profuse diarrhoeal stool (rice water stool)
Which results in severe dehydration, loss of minerals, increased blood
acidity and haemoconcentration.
C. Plague : (bacterial diseases)
Plague is caused by the bacterial species Yersinia pestis, a non motile
gram negative bacilli. There are two types of plagues. They are bubonic
plague and pneumonic plague. Bubonic plague is characterized by enlarged
and inflamed lymph glands (Bubos). The symptoms are shivering, fever,
nausea, vomiting and general weakness. In untreated cases the bubonic plague
can cause 58% mortality. Pneumonic plague is a pneumonia characterized
by a thin watery sputum with bright red streaks of blood. The mortality is
100% in untreated cases.
D. Syphilis : (bacterial diseases)
The disease syphilis is a well known and dreadful sexually
transmitted disease (STD). It is caused by Treponema pallidium. Syphilis
occurs only in humans and is transmitted by direct sexual contact (Venereal
syphilis) or through placenta from an infected mother to the foetus
(Congenital syphilis). Venereal syphilis progresses in three stages viz.,
primary, secondary and tertiary stage. The symptoms are very prominent in the tertiary stage. It will lead to blindness, loss of hearing, brain damage,
insomnia, headache and delusions and spinal cord damage.
E. Gonorrhoea : (bacterial diseases)
Gonorrhoea is another sexually transmitted disease caused by
Neisseria gonorrhoea. In the males the primary site of infection is the
urethra. In the female it is the cervix. It causes pain during urination and a
yellowish discharge from the urethra of males. In females also it causes
painful urination and vaginal discharge. Other symptoms are fever,
abdominal pain, arthritis, meningitis etc.
