infectious diseases of human beings

1. Infectious diseases, also known as transmissible diseases or
communicable diseases comprise clinically evident illness
(i.e., characteristic medical signs and/or symptoms of disease)
resulting from the infection, presence and growth of
pathogenic biological agents in an individual host organism
Infectious diseases of
human beings
The term infectivity describes the ability of an organism to enter,
survive and multiply in the host, while the infectiousness of a disease
indicates the comparative ease with which the disease is transmitted
to other hosts

2. Transmission:-
Transmission of pathogen can occur in various ways including physical contact,
contaminated food, body fluids, objects, airborne inhalation, or through vector
organisms.
Classification:-
Among the almost infinite varieties of microorganisms, relatively few cause
disease in otherwise healthy individuals
The appearance and severity of disease resulting from any pathogen
depends upon the ability of that pathogen to damage the host as well as
the ability of the host to resist the pathogen.
Primary pathogens cause disease as a result of their presence or activity
within the normal, healthy host, and their intrinsic virulence (the severity of
the disease they cause) is, in part, a necessary consequence of their need to
reproduce and spread.
Primary pathogens

3. Opportunistic pathogens:-
Opportunistic disease may be caused by microbes that are ordinarily in
contact with the host, such as pathogenic bacteria or fungi in the
gastrointestinal or the upper respiratory tract, and they may also result from
microbes acquired from other hosts, or from the environment as a result of
traumatic introduction
Transmission:-
Transmission may occur through several different mechanisms. Respiratory
diseases and meningitis are commonly acquired by contact with aerosolized
droplets, spread by sneezing, coughing, talking, kissing or even singing.
Gastrointestinal diseases are often acquired by ingesting contaminated food
and water. Sexually transmitted diseases are acquired through contact with
bodily fluids, generally as a result of sexual activity. Some infectious agents may
be spread as a result of contact with a contaminated, inanimate object (known
as a fomite), such as a coin passed from one person to another, while other
diseases penetrate the skin directly

4. Causes of Infectious Diseases
• Also known as communicable diseases, infectious diseases (in FEK shus) are
caused by organisms or viruses that enter and multiply within the
human body.
• Microorganisms (my kroh AWR guh niz ums) are organisms that can be seen
only through a microscope.
• Microorganisms and viruses that cause disease are called pathogens (PATH
uh junz).
• Pathogens can cause an infectious disease when they enter your body
and multiply.
Bacteria
• Bacteria (bak TEER ee uh) are simple, single-celled microorganisms.
Bacteria live in air, soil, food, and in and on the bodies of plants and
animals, including you.
• Some bacteria injure cells by giving off poisons called toxins (TAHK sinz).

5. Viruses
• The smallest pathogens are viruses.
• A virus can multiply only after entering a living cell.
• The virus then takes over the cell’s reproductive
mechanisms, resulting in cell damage or death.
Protozoans
• Single-celled organisms that are much larger and
more complex than bacteria are known as
protozoans (proh tuh ZOH unz).
Protozoans have the ability to move
through fluids in search of food.
Other Pathogens
Some infectious diseases are caused by animals
such as mites, lice, and certain worms.

6. Prevention:-
Washing one's hands, a form of hygiene, is the most effective way to prevent the
spread of infectious disease
Precautions used in healthcare settings to prevent and control infection

7. Diagnosis of infectious disease sometimes involves identifying an
infectious agent either directly or indirectly. In practice most minor
infectious diseases such as warts, cutaneous abscesses, respiratory
system infections and diarrheal diseases are diagnosed by their
clinical presentation.
There are some infectious diseases of human that are caused by
virus , bacteria and fungi these are as follow.
viral diseases
Diseases that are spread by virus are called viral diseases.
Diagnosis:-
the common viral diseases spread by airborne transmission

8. Smallpox (Variola)
• Caused by variola virus
– large, brick
-shaped complex virus
– linear dsDNA
• Transmitted by aerosol or contact
– humans are the only natural host
Clinical Forms of Smallpox
• Once highly prevalent
– no longer in human populations
– potential bioterrorism agent
• Variola major
– most common, severe form
– extensive rash and higher fever
– 33% fatality rate
There are some common viral diseases

9. • Variola minor
– less common form and less severe
– fatality rates of 1% or less
• Both forms usually transmitted by direct and fairly prolonged face-to-face
contact
• 1977 – last case from a natural infection occurred in
Somalia
• Why eradication was possible –
– disease has obvious clinical features
– humans are only hosts and reservoirs
– there are no asymptomatic carriers
– short infectivity period (3–4 weeks)
Eradication of Smallpox :-

10. Protection from Smallpox:-
• Obtained from vaccination
– use vaccinia virus in a live virus vaccine
• Routine immunization no longer done in the U.S.
• Use of vaccine is controversial because of its unknown efficacy in
the prevention of bioterrorism and potential side effects
• Food and Drug Administration has not approved any treatment for
smallpox
Measles (Rubeola):-
• Measles – rash caused by measles virus (RNA virus)
– enters body through respiratory tract
Subacute sclerosing panencephalitis
– rare progressive degeneration of central
nervous system caused by measles virus
Treatment, prevention, and control –
symptomatic/supportive therapy – attenuated
MMR vaccine (measles, mumps, rubella)

11. Mumps:-
Caused by mumps virus, RNA virus
• Clinical manifestations
– develop 16–18 days after infection
– fever, and swelling and tenderness of salivary glands
– complications include meningitis and orchitis (inflammation of testis)
Treatment, prevention, and control
– symptomatic/supportive therapy
– live, attenuated vaccine (MMR)
Respiratory Syndromes and Viral Pneumonia :-
• Caused by viruses called acute respiratory viruses
• Clinical manifestations – rhinitis, tonsillitis, laryngitis, bronchitis, and
pneumonia
– vary in degree of severity
• Treatment, prevention, and control – in most cases,
symptomatic/supportive therapy

12. Respiratory Syncytial Virus (RSV) :-
• In children, the most dangerous respiratory infection
• RSV is negative strand RNA virus
– causes formation of syncytia (fused cells)
• Spread by hand contact and respiratory secretions
• Clinical manifestations
– acute onset of fever, cough, rhinitis, nasal congestion – may progress quickly
to bronchitis/viral pneumonia
• Treatment, prevention, and control
– rapid immunologic tests
– inhaled ribavirin and RSV-immune globulin – isolation, protective clothing,
and hand washing

13. Rubella (German Measles):-
• Enveloped RNA virus
• Mild brief rash acquired from respiratory droplets
• Congenital rubella syndrome
– disastrous disease in the first trimester of pregnancy
– can lead to fetal death, premature delivery, or
congenital defects • Attenuated vaccine reduced cases
to 1000 and 10 congenital rubella cases per year
• Arboviruses
– viruses transmitted by bloodsucking arthropods from one vertebrate host to
another
– multiply in tissues of vector without producing disease
• vector acquires a lifelong infection
Clinical Syndromes • Arboviral disease syndromes can be placed into three subsets
– Undifferentiated fevers, with or without rash
– Encephalitis
– Hemorrhagic fevers
• Supportive treatment, no vaccines available

14. Equine Encephalitis
• RNA virus causing disease transmitted to humans by mosquitoes – a spectrum
of symptoms which can ultimately result in death
• Genetically distinct strains found in different geographic locations – e.g.,
Western equine encephalitis (WEE) and Eastern equine encephalitis (EEE) strains
• No vaccine available
West Nile Fever (Encephalitis):-
• Caused by a flavi virus, RNA virus • Appeared in New York in 1999 causing
human and animal deaths
• Transmitted to humans by Culex spp., mosquitoes that feed on sparrows and
crows
• Human to human spread has occurred through blood and organ donation
• Only one antigen type exists and immunity is presumed to be permanent
Clinical manifestations
– fever, lymphadenopathy, rash
• Treatment, prevention, and control
– serology tests – supportive treatment – mosquito control measures

15. Acquired Immune Deficiency Syndrome (AIDS) :-
• Caused by human immunodeficiency virus (HIV) – RNA virus family Retroviridae
HIV Transmission:-
• When infected blood, semen, or vaginal secretions come in contact with
uninfected person’s broken skin or mucous membranes
HIV Life Cycle:-
• Integrates into host cell’s DNA as a provirus
• Can remain latent – asymptomatic
• Can direct synthesis of viral RNA synthesis of new viral particles – new virion
are assembled and released through budding and eventual lysis
Course of Disease
• Some patients rapidly develop clinical AIDS; die within 2–3 years
• Some patients remain relatively healthy for at least 10 years post infection
• In majority of patients HIV infection progresses to AIDS in 8–10 years

16. • Acute – 2–8 weeks after infection
– most experience brief illness called acute retroviral syndrome
• Asymptomatic (latent) – may last from 6 months to 10 or more years –
levels of detectable HIV in blood decrease, although viral replication continues
CDC Classification System for Stages of HIV-Related
Conditions
• Chronic symptomatic – formerly called AIDS-related complex
– can last for months to years
– viral replication continues
– numbers of CD4+ cells in blood significantly decrease
• results in patients developing a variety of illnesses often caused by
opportunistic pathogens and AIDS related cancers
• AIDS
– fourth and last stage – immune system no longer able to defend against virus •
Definition of AIDS
– all HIV-infected individuals who have fewer than 200 CD4+ T cells/microliter of blood
or a CD4+ cell percentage of lymphocytes of less than 14
39

17. Central Nervous System Disease Caused by HIV:-
• Headaches, fever, subtle cognitive changes, abnormal reflexes, and ataxia
• Dementia and severe sensory and motor changes observed in advanced cases
• Autoimmune neuropathies, cerebrovascular disease, and brain tumors are
common
Diagnosis
• Viral isolation and culture
• Assays for reverse transcriptase activity or viral antigens
• Most commonly done by detection of specific anti-HIV antibodies in the blood
Treatment
• No cure for AIDS
• Treatment directed at reducing viral load, disease symptoms, and treating disease
and malignancies
Prevention and Control
• Achieved primarily though education
• Barrier protection from blood and body fluids
• Not sharing intravenous needs or syringes
• Continued screening of blood and blood products

18. Vaccine • Not available but ongoing research
• Ideal vaccine
– would stimulate the production of neutralizing antibodies which would bind
to virus preventing it from entering host cells
– promote formation of cytotoxic T cells capable of destroying cells infected
with virus
Cold Sores:-
• Fever blisters (herpes labialis)
• Usually caused by herpes simplex virus type 1
(HSV-1); rarely herpes simplex virus type 2
(HSV-2) – enveloped dsDNA virus with
icosahedral capsid
• HSV infect epithelium at oral sites
– virus enters cells, migrates to nucleus
– active infection
• explosive multiplication of virus – latent
infections
• virus moves to trigeminal ganglion and is
nondetectable unless reactivated

19. • Treatment, prevention, and control
– diagnosis by ELISA, direct fluorescent antibody screening of tissue or PCR
– acyclovir and other antivirals
– no vaccine, education important
• Clinical manifestations
– characteristic blister at site of inoculation
– gingivostomatitis – lips, mouth, and gums
– herpetic keratitis – cornea
– lifetime latency develops, with periodic reactivation in times of stress
Common Cold
• Caused by many different rhinoviruses (ssRNA viruses); also by corona-
viruses and parainfluenza viruse
• Seasonal peaks and transmitted by: –
excretion of virus in nasal secretion
– airborne transmission by droplets
– contaminated hands or fomites
• Symptomatic/supportive therapy

20. Cytomegalovirus Inclusion Disease
• Worldwide distribution – caused by human cytomegalovirus (HCMV)
– dsDNA virus, Herpesviridae
– enveloped icosahedral capsid
– HCMV can infect any cell of the body
– causes formation of intra- nuclear inclusion bodies and cytoplasmic
inclusions
• Treatment, prevention, and control – antiviral agents used for high-
risk patients – avoiding close personal contact with infected individual – blood
transfusions and organ transplants from seronegative donors
Genital Herpes
• Usually caused by herpes simplex type 2
– linear dsDNA
– enveloped virus
• Very common sexually transmitted disease and to infant during vaginal delivery
(congenital or neonatal herpes)
• Active and latent disease with reactivations

21. Human Herpesvirus 6 Infections
• HHV-6
– enveloped with icosahedral capsid
– dsDNA
– tropism is wide, including CD8+, CD4+, natural killer, and epithelial cells
– proviral DNA in human chromosomes
• Probably transmitted in saliva
• Clinical manifestations
– exanthem subitum
• short-lived disease of infants
• high fever for 3 to 4 days, followed by macular rash
• No treatment or prevention measures

22. Human Parvovirus B19 Infections
• Icosahedral, naked virus with ssDNA genome
– genome so small that virus uses overlapping reading frames –
tricks host into copying viral DNA
• Significant human pathogen
• Infection thought to be by respiratory route
• Mild symptoms (fever, headaches, chills, malaise) in most normal
adults
• Treatment, prevention, and control
– passive immunization with anti-B19 antibodies
– infection usually followed by lifelong immunity
– hand washing is best prevention for disease

23. Mononucleosis (Infectious)
• Caused by Epstein-Barr virus (EBV)
– herpes virus
– dsDNA, icosahedral with envelope
– infects B cells
– also associated with Burkitt’s lymphoma and nasopharyngeal carcinoma
• Spread by mouth-to-mouth contact
• Clinical manifestations
– enlarged lymph nodes and spleen, sore throat, headache, nausea, general
weakness and tiredness, and mild fever
– self-limited disease, lasting 1 to 6 weeks
• Treatment, prevention, and control
– rapid diagnostic tests
– symptomatic/supportive therapy

24. • Hepatitis
– inflammation of liver
– caused by 11 different viruses
• 2 herpesviruses—Epstein-Barr virus (EBV) and cytomegalovirus (CMV)
– cause mild, self-resolving disease
– no permanent hepatic damage
– signs and symptoms include fatigue, nausea, and malaise
Viral Hepatides
Hepatitis B (Serum Hepatitis)
• Hepatitis B virus (HBV)
– dsDNA virus
– Dane particle is infectious virion
– transmitted through body fluids and intravenous equipment
– can pass the placenta and breast milk

25. • Clinical signs
– most cases asymptomatic
– generalized symptoms occurs after 1–3 month incubation period – virus
infects liver hepatic cells causing liver damage • yellow appearance
(jaundice) results from bilirubin accumulation
• Prevention and control:-
– passive immunotherapy within 7 days of exposure
– excluding contact with contaminated materials
– vaccination of high-risk groups
• 0–18 year olds
• contacts of carriers
• health-care professionals
Hepatitis C Virus (HCV)
• RNA virus in Flaviridae family
– multiple genotypes
• Transmission virus contaminated blood, fecal oral route, also spread from
mother to fetus, and through organ transplants

26. • Chronic infection common
• Leading cause of liver transplant in U.S.
• Treatment, prevention, and control
– ELISA test for antibodies and PCR for nucleic acid
– combination therapy of Ribovirin and recombinant interferon-alpha
Hepatitis Delta Virus (HDV)
• Delta agent, RNA virus discovered in 1977
• Dependent on HBV to provide the envelope protein (HbsAG) for HDV
RNA genome
– similarities to viroids and virusoids
• Transmission by body fluids
• Causes severe acute and chronic hepatitis in HBV infected
• Treatment, prevention, and control
– serological tests for anti-HDV antibodies
– no satisfactory treatment

27. Warts
• Verrucae - horny projections on skin associated with human papillomaviruses
• Four major types
– plantar warts
– verrucae vulgaris
– flat or plane warts
– anogenital condylomata (genital warts)
• Direct contact and autoinoculation
• Treatment – physical destruction, topical application of drug
podophyllum, or injection of IFN-α
Gastroenteritis (Viral)
• Acute viral gastroenteritis
– inflammation of stomach or intestines
– important disease of infants and children
– leading cause of childhood death in developing countries
– probably spread by fecal-oral route

28. • Caused by four major groups of viruses
• Rotavirus, adenovirus, and astrovirus
– ~5–10 million deaths/year worldwide
– viral diarrhea transmitted by fecal oral route
– rotavirus live oral vaccines
• Norovirus
– ~23 million cases of acute gastroenteritis per year
– usually self-limited disease
– symptomatic/supportive therapy
Hepatitis A Virus
• Infectious hepatitis
• Spread by fecal-oral contamination of food, drink, or shellfish
• Clinical manifestations – usually mild intestinal infection
• anorexia, general malaise, nausea, diarrhea, fever, and chills – occasionally
viremia occurs leading to liver infection
• jaundice
• Treatment, prevention, and control – immunodiagnostic tests for HAV
antibodies – simple hygienic measures, sanitary disposal of excreta, and killed
HAV vaccine

29. Hepatitis E Virus
• implicated in many epidemics in developing countries
• transmission by fecal contaminated water
•similar to HAV course of disease
• ~15%–25% fatality rates in pregnant women
Poliomyelitis
• Polio (infantile paralysis)
• Caused by poliovirus
• Clinical manifestations – usually asymptomatic or brief, mild illness
• fever, headache, sore throat, vomiting, loss of appetite – viremia sometimes
occurs
• usually transient; no clinical disease
• sometimes persists and virus enters central nervous system causing paralytic
polio
• Prevented by immunization with live vaccine and killed vaccine
• Likely to be the next human disease to be completely eradicated

30. Zoonotic Diseases
• Human viral infections in animal reservoirs before transmission to and between
humans
• RNA viruses, many are on Select Agents list as potential bioweapons
– Ebola and Marburg viruses
– hantaviruses
– Lassa fever virus
– Nipah virus
Ebola and Marburg Hemorrhagic Fevers
• Viral hemorrhagic fever (VHF)
– severe multisystem syndrome caused by many distinct viruses
– overall host vascular system is damaged leading to vascular leaking
(hemorrhage) and dysfunction (coagulopathy)
• Transmission from direct contact with Ebola victim, body fluids or clinical
samples
• Internal hemorrhaging
• Supportive therapy; no treatment available
• Experimental vaccines being evaluated

31. Marburg Hemorrhagic Fever
• Genetically unique RNA virus in Filoviridae
• Rare, severe disease that affects human and nonhuman primates
• Indigenous to Africa
• Definitive animal host not identified
• Symptoms come on abruptly and become increasingly severe multi-organ
dysfunction
• Supportive therapy but no specific treatment available
Hantavirus Pulmonary Syndrome (HPS)
• Single-stranded, negative sense RNA virus in Bunyaviridae family
• Transmitted to humans by inhalation of virus particles shed in urine, feces, or
saliva of infected rodents
• Potentially deadly for humans but do not cause disease in their reservoir
(rodent) hosts
• Supportive therapy but no specific treatment available

32. Rabies
• Caused by different strains of rabies virus
– negative strand, bullet shaped, RNA virus
– highly neurotropic
• Transmitted by: – bites of infected animals
– aerosols in caves where bats roost
– contamination of scratches, abrasions, open wounds, or mucous
membranes with saliva of infected animals
Clinical manifestations – begins 2 to 16 weeks after exposure
– pain or paresthesia at wound site, anxiety, irritability, depression, fatigue, loss of
appetite, fever, and sensitivity to light and sound
– quickly progresses to paralysis
– death results from destruction of regions of the brain that regulate breathing
• Treatment, prevention, and control
– numerous diagnostic tests, including rapid immunodiagnostic tests
– postexposure vaccination
– preexposure vaccination of individuals with high risk of exposure, dogs, and
cats

33. Prion Diseases
Transmissible spongiform encephalopathies
– fatal neurogenerative disorders caused by prions
– remains clinically silent for months or years
– ends in profound disability or death
• Transmission – medical procedures, genetic, food-borne
• Prions (protein infectious particles) consist of abnormally folded proteins
(PrPsc) which can induce normal forms of protein PrPc to abnormally fold
• BSE agent survives gastrointestinal tract passage, and is neurotropic, both
serve as source of agent
• Transmitted from cattle with bovine spongiform encephalopathy (BSE) or mad
cow disease
• Cattle experimentally infected with BSE test positive for prion agent

34. Chickenpox (Varicella) and Shingles (Herpes Zoster)
• DNA virus, member of Herpesviridae
• Humans serve as reservoir and source
• Acquired by droplet inhalation into respiratory
system
• Chickenpox – results from initial infection
– vaccine prevents or shortens illness
• Treatment – supportive; acyclovir and others
Influenza (Flu)
• Respiratory system disease caused by influenza virus
• Clinical manifestations
– chills, fever, headache, malaise, and general muscular
aches and pains
– recovery usually within 3 to 7 days
– often leads to secondary infections by bacteria
• Treatment, prevention, and control
– rapid immunologic tests
– symptomatic/supportive therapy – inactivated virus
vaccine

35. Bacterial diseases
Diseases that are caused by bacteria are called bacterial diseases. Some
common bacterial diseases are as follow .
Diarrhoea
Diarrhoea is a clinical syndrome in which there is frequent passage of unusually
loose or watery bowel movements, usually three or more in a 24 hour period,
sometimes accompanied by vomiting and fever, abdominal pain or cramps, faecal
urgency, tenesmus, or the passage of bloody or mucoid stools.
Mode of transmission Infectious diarrhoea is spread by the faecal-oral
route. The most common sources are contaminated food and water, person-
to-person contact and direct contact with infected faeces.
Diagnosis The diagnosis of infective diarrhoea is dependent upon the identification
of the causative pathogen from the faeces by culture, antigen detection or by light
microscopy (in the case of parasites).

36. Treatment The main principles of treatment are as follows:
• Watery diarrhoea requires fluid and electrolyte replacement, irrespective of
its aetiology
• Feeding should be continued during all types of diarrhoea to the greatest
extent possible, and should be increased during convalescence so as to avoid
any adverse effect on nutritional status.
• Antimicrobials and antiparasitic agents should not be used routinely; most
episodes, including severe diarrhoea and diarrhoea with fever do not benefit
from treatment with antimicrobials or antiparasitic agents.
Typhoid
Typhoid fever (also known as enteric fever) is a severe systemic infection
caused by the Gram negative bacterium Salmonella typhi.
The organisms are absorbed from the gut and transported via the blood
stream to the liver and spleen. They are released into the blood after 10 to
14 days. This is when the symptoms begin. The organisms localise in the
lymphoid tissue of the small intestine, which can bleed and perforate. This
is the main cause of death from typhoid fever.

37. Mode of transmission Typhoid fever is spread via the faecal-oral route,
usually through contaminated food and water. Organisms only infect humans, so
spread comes from infected excreta of a human with typhoid, or from a carrier.
Polluted water is the most common source of typhoid, but shellfish gathered
from sewage-contaminated beds and raw vegetables fertilized with night soil are
high-risk foods
Manifestations
• In the early stages fever, severe headache, constipation and a dry cough may
be present.
• The fever rises in a “step ladder” pattern for 4 or 5 days.
• Abdominal tenderness and an enlarged liver or spleen may occur.
• The pulse can often be slower than would normally be anticipated considering
the patient’s temperature.
• After 7 to 10 days, the fever reaches its peak and a rash may appear on the
upper abdomen and back as sparse, slightly raised, rose-red spots, which fade
on pressure and are usually only visible on white skin.
• Diarrhoea may develop later, together with bronchitis; the patient may also
show signs of confusion.

38. Diagnosis Blood culture is the most important method for diagnosis.
Isolation of the organism from the stool is more common in the second and
third weeks of the illness. In some cases, isolation of the bacteria in the urine
can be used as a diagnostic method.
Methods of treatment
Four different antibiotics are often used for treatment: Ciprofloxacin,
Cotrimoxazole, Amoxycillin and Chloramphenicol. Unfortunately, as with many
Salmonella, S. typhi is becoming resistant to many antibiotics and some isolates
are only sensitive to Ciprofloxacin. Treatment must continue for two weeks (10
days in the case of Ciprofloxacin) and it is common for the patient to remain
pyrexial for five days following commencement of treatment. Effective
treatment does not always prevent complications, the disease recurring or the
patient becoming a carrier. A chronic carrier may be treated for four weeks
with aminoquinalones and in some cases it may be necessary to perform a
cholecystectomy, as the gallbladder can act as a reservoir for the S. typhi
organisms.

39. Anthrax
Anthrax is an acute infectious disease caused by the spore forming bacterium
Bacillus anthracis. It is primarily a disease of herbivorous animals, but it can infect
all mammals including humans. The B. anthracis spores can be found in animal
products such as wool, hair, hides, skins, bones, bonemeal and the carcasses of
infected animals. The spores can survive in the soil for many years.
Modes of transmission There are three main modes of transmission:
• direct contact with skin – infection is passed on by the handling of
contaminated animal products, resulting in a cutaneous infection. This is the
most common route.
• airborne – spores are inhaled causing respiratory infection; and
• faecal/oral – when undercooked meat from an infected animal is eaten
causing gastrointestinal (GI) infection.
Methods of treatment
To be effective, treatment should be initiated as soon as possible. Mild cases of
cutaneous anthrax may be effectively treated with oral Penicillin or a tetracycline.
Antibiotic therapy does not affect the healing process or evolution of the skin
lesion, but it can prevent systemic symptoms from developing.

40. Topical therapy is not effective. If the infection is spreading or if systemic
symptoms are present, high dose parenteral antibiotic therapy should be given.
Treatment of inhalation or gastrointestinal anthrax requires high dose
intravenous Penicillin.
Legionnaire’s disease
Legionnaire’s disease is caused by the gram-negative bacillus legionella pneumophila,
found widely in soil and water.
Mode of transmission Legionella is transmitted via droplet or aerosol
inhalation of infected water. Hot water tanks, cooling towers, and shower
heads all act as foci of infection.
Manifestations • May be asymptomatic
• A mild self-limiting febrile illness may occur.
• A severe, potentially fatal progressive illness with malaise, myalgia, and a rapidly
rising fever with rigors and an unproductive cough may develop.
• Progressively worsening symptoms can occur within a few days, including pleuritic
chest pain, vomiting, abdominal pain, confusion, neuropathy and clouding of
consciousness.

41. Diagnosis Clinical suspicion of this disease can be confirmed with sputum cultures and
serum antibody levels. Early diagnosis can be made by the detection of antigen in urine.
Treatment Intravenous Erythromycin and/or oral Rifampicin is the treatment of
choice,
Lyme disease
Lyme disease is an infection caused by the bacteria Borrelia burgdorferi.
Mode of transmission Borrelia burgdorferi is transmitted in tick (Ixodes
ricinus) saliva when the tick bites the host.
The ticks feed on blood by inserting their mouthparts into the skin of the host
animal, but because they are slow feeders, a complete blood meal can take
several days. As they feed their bodies slowly enlarge.
Diagnosis The diagnosis is established from the clinical picture, a possible
exposure to tick bites and the detection of antibodies, which are normally
detectable around 4–6 weeks after exposure.

42. Methods of treatment At the early-localized stage, it can be successfully treated
with antibiotics (Amoxycillin or tetracyclines). Treatment at the later stage is with long-term
(4 weeks or more) antibiotics such as cefotaxime (I.V.) or doxycycline. Patients will require
support and reassurance throughout this debilitating illness.
Tetanus
Tetanus is caused by infection of wounds by the bacterium Clostridium tetani,
which produces a toxin that damages the nervous system and muscles.
Mode of transmission The bacterium Clostridium tetani is found in the
intestinal tracts of man and animals, where it remains harmless and causes no
disease. However, spores are produced which are passed in the faeces, and
contaminate the environment. These spores can persist for years in soil and dust
and are resistant to heat, drying, chemicals and sunlight.
Tetanus spores enter open wounds at the time of an injury (traumatic wounds,
animal bites or burns). The wound need not be serious. In countries where
hygiene standards are poor, there is a high incidence of neonatal tetanus, where
spores enter and infect the babies through the umbilical cord. Tetanus cannot be
spread directly by personto-person contact.

43. Treatment Deep penetrating wounds provide ideal conditions for bacteria to
develop so these should be surgically opened and debrided. Antibiotic therapy
(Metronidazole or Penicillin) should be given.
Patients with mild muscular spasms may be treated with infusions of diazepam.
For more severe cases, where autonomic instability presents, intensive medical
care with assisted ventilation and muscle relaxants may be required.
Diphtheria
Definition Diphtheria is a serious bacterial infection, usually of the throat, caused
by Corynebacerium diphtheriae. The throat infection may obstruct breathing and
cause death. The important feature of an isolate of C. diphtheriae is whether it is
able to produce toxins. There are many harmless nontoxigenic strains of C.
diphtheriae which may be carried in the throat. If the strain is toxin producing, the
exotoxin becomes fixed on tissues unless neutralised by circulating antitoxin. The
exotoxin can cause damage to other organs such as the heart, kidneys and nerves
and can result in death.
Mode of transmission Diphtheria is spread from person to person by
droplets from the respiratory tract of a carrier or patient, or via the discharge
from cutaneous lesions

44. Antibiotics are used to destroy toxin producing organisms and to shorten the period of
infectivity. Penicillin is given, or if allergic to Penicillin, Erythromycin is used.
Methods of treatment
Prevention of spread The primary means of preventing spread is by
diphtheria immunization
Pertussis
Pertussis (whooping cough) is a highly infectious acute bacterial disease involving
the respiratory tract. The causative bacteria is Bordetella pertussis in more than
90% of cases or more rarely Bordatella parapertussis.
Mode of transmission Pertussis is transmitted by airborne contact with
respiratory secretions of infected persons.
Methods of treatment Erythromycin (see Appendix 4) may eradicate the
bacteria thus shortening the period of infectivity but organisms can reappear
when treatment is stopped. This may reduce the possibility of secondary
infection (if started early enough). Antibiotics do not influence the course of
the clinical disease unless given within the first 5 days of illness when the
diagnosis is often unclear

45. Pneumococcal pneumonia
Streptococcus pneumonia is an important bacterial cause of pneumonia in
adults and children. Pneumococcal pneumonia is the biggest childhood killer.
Other associated diseases caused by Streptococcus pneumonia include otitis
media, sinusitis, mastoiditis, meningitis, and brain abscesses.
Mode of transmission Airborne droplet spread of respiratory secretions.
• Incubation period: 24–72 hours
• Communicability: during the course of active infection or until 24–48 hours of
appropriate antibiotic therapy
Diagnosis Streptococcus pneumonia may be isolated from blood culture,
throat swab and naso-pharyngeal aspirate.
Methods of treatment Amoxycillin or Benzylpenicillin. Penicillin resistant
pneumococcal infection may respond to high dose Benzylpenicillin.
Erythromycin, Cefuroxime or Tetracycline can be given if the patient is allergic
to Penicillin. Avoid Cephalosporins if immediate type Penicillin allergy
suspected. In some countries, up to half of the most common forms of
pneumonia are resistant to penicillin, the first line drug

46. Tuberculosis (TB)
Tuberculosis is a disease caused by organisms classified as Mycobacterium.
There are three main types:
Mycobacterium tuberculosis: the main cause of tuberculosis globally;
Mycobacterium bovis: causes disease in cattle and other animals, as well as in
humans; and,
Mycobacterium africanum: occurs in Africa.
Modes of transmission Mycobacterium bovis can be transmitted to
humans from animals through the air, or indirectly by drinking contaminated
milk.
Manifestations of TB The majority of people infected with Mycobacterium
tuberculosis remain well. Around 10% of those infected will go on to develop
the disease; half will do so within a year following infection, and the other half
over the next 60 years or so. This can vary according to the intensity and
duration of exposure. Immuno compromised patients and other vulnerable
groups are more likely to develop the disease (See risk factors).

47. Treatment for patients with liver disease Patients with the following conditions
can receive the usual short-term course chemotherapy regimens, provided that
there is no clinical evidence of chronic liver disease: hepatitis virus carriage, a
past history of acute hepatitis, excessive alcohol consumption
Treatment
Protozoans
Some infectious diseases are also caused by protozoans.
Some of these are as follow
Leishmaniasis
Leishmaniasis is caused by the protozoan Leishmania
Mode of transmission Leishmaniasis is transmitted to humans by the
female sand fly. The sandfly bites on an animal or human in order to obtain a
blood meal to develop its eggs. If this blood contains the Leishmania parasites,
these will continue to develop inside the sandfly over a period of 4–25 days.
When the sandfly feeds again on a fresh source, transmission of the disease
continues.

48. There are two types of leishmaniasis infection, cutaneous leishmaniasis (CL) and
visceral leishmaniasis (VL). CL, the less serious form of infection, can be
transmitted to humans from humans, via the bite of a sandfly. VL, the more
serious form of infection, can only be transmitted to humans from animal hosts,
via the bite of a sandfly. The dog is the main reservoir of infection
Treatment Most “dry” lesions found in CL are self-limiting and require no
treatment other than protection from secondary infection with the use of
simple dressings.
Patients with VL should be hospitalised until stable. Their nutritional status and
potential deficiencies must be addressed, and any associated bacterial
infections promptly diagnosed and treated. Most cases of VL respond to
parenteral “pentavalent organo-antimony” drugs. These are given over a
period of 30 days, but haematological and parasitological follow up should
extend to one year to prevent any relapse. Unfortunately, HIV infected
individuals have a very poor response to therapy
Prevention of spread This is dependant upon:
• control of the sandfly population through reducing breeding sites such as
dark, moist habitats (cracks in masonry, piles of rubble and the bark of dead
trees.)

49. Definition Malaria is caused by a protozoan parasite. There are four
Plasmodium species that affect humans. Plasmodium falciparum causes the
most dangerous type of malaria and can quickly cause life threatening
cerebral malaria and multi-organ failure if left untreated or not treated
properly. Plasmodium vivax, Plasmodium ovale, and Plasmodium malaria
cause the other three types of malaria which can cause significant
morbidity, but which rarely causes death.
Malaria:-
Modes of transmission:-
The modes of transmission are:
• via the bite of the female anopheline mosquito, mainly during the night.
This is by far the most common mode of transmission; and
• by direct transmission via blood transfusion, sharing of drug injecting
equipment, or by needle stick injury.

50. Diagnosis:-
A presumptive clinical diagnosis can be made in the absence of laboratory
facilities or when rapid results are not available for any person with a fever or
flu-like symptoms, who lives within or has been in a malarious area,
excluding other obvious causes of fever.
Thick and thin blood films can confirm malaria; the thick, stained film can
reveal white cells and parasites which can be too scanty to see on normal
thin films, whereas species identification is performed on the thin blood film.
Plasmodium falciparum may be seen on a blood film 9 days after infection,
but it may take weeks or months before the other species can be seen.
Repeat examinations may be required.
In certain circumstances, rapid immunological tests (dipstick) can be used.

51. Methods of treatment:-
Methods of treatment Treatment involves:
• elimination of the asexual parasites from the blood with schizontocidal
drugs;
• recognition and management of any complications; and
• provision of supportive measures.
Louse-borne typhus
Louse-borne typhus is a rickettsial disease caused by Rickettsia prowazekii.
Mode of transmission Rickettsia prowazekii is transmitted by the human
body louse Pediculus humanus. The lice become infected while feeding on
the blood of a patient with acute typhus fever. Infected lice then excrete
rickettsia in faeces when feeding on a second human host. The rickettsia
enter humans through rubbing or scratching either infected faecal matter or
crushed lice into the bite wound or any other entry site on the skin.
Manifestations • Incubation period is 1–3 weeks.
• Abrupt fever, severe headache and myalgia present.
• The fever remains high and unremitting.
• A fine pink macular rash spreads from the upper trunk to the whole body.

52. Treatment If treatment begins before serious complications occur, the risk of
fatal illness is virtually eliminated. Treatment is a single dose of 200 mg
doxycycline, regardless of the patient’s age.
Prevention of spread Prevention is through:
• Cleanliness to prevent body louse infestations
• Delousing measures with insecticides and efforts to improve living conditions
Tickborne encephalitis
Modes of transmission The virus responsible for this disease is
transmitted to man in two ways:
• via the bite of an infected tick (Ixodes ricinus); and,
• by ingestion of unpasteurised milk from infected animals, usually goats.
(Very rarely is it transmitted in this manner.)
The reservoir of infection found is in rodents, birds, goats and cattle. It cannot
be spread directly from human to human.

53. Manifestations • The incubation period is 1–2 weeks.
• A flu like illness lasting for a few days presents.
• The illness may produce no further symptoms.
• In approximately 25% of cases, a second phase will develop after 10 days,
characterised by severe headache and fever
Treatment Post-exposure prophylaxis with specific human immunoglobulin
can be initiated following a potentially infectious tick bite, but there is no
specific treatment for this disease once established.
Prevention of spread This is dependent upon:
• Avoidance of tick bites. Those at risk should wear protective clothing (long
trousers and socks), and use an insect repellent. Skin should be inspected for
ticks every few hours and any ticks found should be removed immediately.
• Those living in endemic areas should be aware of the disease and how it is
transmitted.

54. Toxoplasmosis
Toxoplasmosis is an infection caused by the single celled parasite Toxoplasma
gondii.
Mode of transmission
• Faecal-oral spread through eating poorly cooked meats, especially pork and
mutton. Cysts are harboured in the animal’s tissues but are not excreted in the
faeces.
• Faecal-oral spread through contact with cat’s faeces. Members of the cat
family are known definitive hosts for T. gondi and thus are the main reservoirs
for infection; the parasites are excreted in the cats’ faeces and can remain in the
soil or environment for many months.
Diagnosis is by serological testing. The diagnosis of endophthalmitis is by
culture of vitreous humour
Treatment
Treatment is usually with oral pyremethamine and sulphonamide. Hospital referral is
essential for infants with endophthalmitis.