Common Diseases in Humans - 2

Some Diseases caused by Bacteria

Bacterial diseases are illnesses caused by pathogenic bacteria. While many bacteria are harmless or beneficial, a number of bacterial species cause diseases in humans. For each disease below we describe the causative organism, mode of transmission, typical symptoms, diagnosis, treatment and prevention. Where relevant, key facts from the reference text are retained.

1. Typhoid

Definition and causative organism: Typhoid fever is a systemic infectious disease caused by the bacterium Salmonella enterica serotype Typhi (often referred to as Salmonella typhi). Humans are the only known reservoir for this organism.

Important facts: The reference notes the first reported case of typhoid fever in the United States in the early 1900s. Globally, typhoid continues to be an important public-health problem; historically cited estimates indicate around 21 million infections and about 200,000 deaths annually. Studies sometimes refer to different strains or types (for example, designations such as ST1 and ST2 appear in laboratory or epidemiological reports).

Transmission

• The usual route is faecal-oral: ingestion of food or water contaminated with faeces or urine from an infected person (symptomatic or asymptomatic carrier).
• Poor sanitation, inadequate personal hygiene and contaminated drinking water are common risk factors.

Pathogenesis (brief)

• The bacteria invade intestinal mucosa, enter the bloodstream and spread to reticuloendothelial organs (liver, spleen, bone marrow).
• Multiplication in these sites and subsequent release into blood cause the systemic symptoms of typhoid.

Symptoms

• Prolonged high fever that may rise gradually
• Loss of appetite
• Abdominal pain and diarrhoea (sometimes constipation)
• Headache, malaise and weakness
• Sometimes rose-coloured spots on the trunk

Diagnosis

• Blood culture is the gold standard early in disease.
• Stool and urine cultures may detect the organism in later stages or in carriers.
• Serological tests such as the Widal test are used in many settings but have limitations and must be interpreted with clinical and epidemiological context.

Treatment

• Appropriate antibiotics prescribed by a physician (choice depends on local resistance patterns). Historically used drugs include chloramphenicol, ampicillin and co-trimoxazole; cephalosporins and other agents are used depending on resistance.
• Supportive care: hydration, nutrition and monitoring for complications.

Prevention

• Safe drinking water, proper sanitation and hand hygiene are the most effective preventive measures.
• Vaccination (oral live attenuated Ty21a or injectable Vi polysaccharide and newer Vi-conjugate vaccines) is available for travellers or in endemic settings as per public-health recommendations.
• Food safety: avoid food and drinks of uncertain sanitary quality in endemic areas.

2. Pneumonia

What is pneumonia? Pneumonia is an infection of the lungs in which air sacs (alveoli) become inflamed and often fill with fluid or pus. It ranges from mild to life-threatening and can be caused by bacteria, viruses, fungi or atypical organisms.

Types (by causative agent)

• Bacterial pneumonia: Common bacterial cause is Streptococcus pneumoniae. Other bacteria include Haemophilus influenzae, Staphylococcus aureus and Gram-negative bacilli.
• Viral pneumonia: Caused by influenza viruses, respiratory syncytial virus (RSV), coronaviruses and others. Viral causes account for a substantial proportion of pneumonia cases.
• Mycoplasma (atypical) pneumonia: Caused by Mycoplasma pneumoniae; often milder and called atypical pneumonia.
• Fungal pneumonia and others: Less common; occur especially in immunocompromised patients.

How pneumonia develops

• Pathogens reach the lungs by inhalation, aspiration from the upper airway, or spread from the bloodstream.
• If the immune system cannot clear the invading organisms, inflammation and fluid accumulation in alveoli impair oxygen exchange and produce symptoms.

Symptoms

• Cough with sputum that may be greenish, yellowish or blood-streaked
• Shortness of breath and rapid breathing
• Fever with chills
• Sweating, chest pain (worse on coughing or deep inspiration)
• Loss of appetite, nausea and fatigue

Diagnosis

• Clinical examination (inspection, auscultation) and history.
• Chest X-ray to identify consolidation (radiological confirmation).
• Laboratory tests: complete blood count, sputum microscopy and culture, blood cultures in severe cases; antigen and PCR tests for specific pathogens where available.

Treatment

• Bacterial pneumonia: appropriate antibiotics selected according to likely agents and local resistance.
• Viral pneumonia: specific antiviral agents for some viruses (e.g., influenza); many viral pneumonias are managed supportively (fluids, oxygen, nutrition).
• Supportive measures: sufficient fluids, nutrition, antipyretics, oxygen therapy if hypoxic, and hospitalization for severe cases.

Prevention

• Vaccination: Vaccines are available to prevent some causes of pneumonia, e.g., pneumococcal vaccines and influenza vaccine. Schedule and choice depend on age and risk factors.
• Good hygiene: Handwashing and respiratory hygiene reduce transmission of respiratory pathogens.
• Avoid tobacco and limit alcohol: Smoking and excessive alcohol weaken lung defences and increase risk.
• Early treatment of underlying illnesses and good nutrition support immune function.

Key points about pneumonia

• Pneumonia is an infection of the lungs caused by bacteria, viruses or fungi.
• Diagnosis uses clinical examination, radiology and microbiology tests.
• Severity ranges from mild to potentially fatal; treatment depends on the cause.
• Prevention includes vaccines, hygiene and reducing risk factors such as smoking.

3. Common Cold (viral)

What is the common cold? The common cold is an acute, self-limiting viral infection of the upper respiratory tract (nose, nasopharynx and sometimes sinuses). It commonly causes runny nose, sneezing, sore throat and cough.

Causes

A large variety of viruses can cause the common cold. Important ones include:

• Rhinoviruses: A leading cause, often active in early fall, spring and summer; they cause a substantial proportion of colds.
• Coronaviruses: Several types cause common colds, especially in winter and early spring.
• Respiratory syncytial virus (RSV) and parainfluenza viruses: These can cause more severe lower-respiratory infections, particularly in infants.

How it spreads

• Direct contact with infected secretions (touching contaminated surfaces then touching the face).
• Droplet spread from coughing or sneezing; close contact increases risk.
• Virus attaches to the mucous membrane of the nose or throat and begins replicating; the immune response produces the familiar symptoms.

Signs and symptoms

Primary symptoms of the common cold include:

• Sore or scratchy throat
• Sneezing
• Nasal congestion and runny nose
• Cough and watery eyes
• Mucus draining into the throat (post-nasal drip)

Secondary symptoms that may suggest influenza or another more serious infection rather than a simple cold include:

• High fever
• Muscle aches
• Marked fatigue or weakness
• Severe headache and loss of appetite

Prevention

• Hand hygiene: Frequent handwashing with soap or use of an alcohol-based hand rub reduces transmission.
• Avoid touching the face: Reducing contact with nose, mouth and eyes lowers risk.
• Keep surfaces clean: Regularly disinfect commonly touched objects (doorknobs, switches, phones).
• Reduce stress and maintain health: Adequate rest, nutrition and stress management support immunity.
• Avoid smoking: Smoking and passive smoking increase susceptibility to respiratory infections.
• Drink sufficient fluids and use symptomatic remedies (warm fluids, decongestants) as advised.

Myths

• Cold weather, getting wet or chilled, or particular foods do not directly cause a viral cold; infection requires exposure to a virus and susceptibility of the host.
• Large tonsils/adenoids or ordinary dietary choices are not direct causes of the common cold.

Some Diseases caused by Fungi

Ringworm (dermatophytosis)

Definition: Ringworm is a superficial fungal infection of the skin caused by dermatophyte fungi. The term "ringworm" is traditional; it is not caused by a worm. The technical term is dermatophytosis.

Sites and terminology

• Tinea capitis: Scalp ringworm (capitis = of the head).
• Tinea corporis: Ringworm of the body (corporis = of the body).
• Tinea cruris: Groin (jock itch) (cruris = of the leg).
• Tinea pedis: Athlete's foot (pedis = of the foot).
• Tinea unguium refers to nail infections by dermatophytes.

Causes and transmission

• Direct skin-to-skin contact with an infected person.
• Contact with contaminated objects such as towels, combs, clothing, or bedding.
• Transmission from infected animals (pets such as cats and dogs) or contact with contaminated soil.
• Warm, moist conditions, tight clothing and skin folds favour fungal growth.

Symptoms

• Itchy, scaly, red, ring-shaped patches on the skin.
• Scalp infection may cause inflamed, scaly bald patches.
• Infection of nails leads to thickening, discoloration and brittleness.
• Interdigital itching and scaling between toes in tinea pedis.

Diagnosis

• Clinical appearance often suggests the diagnosis.
• Wood's lamp (UV-A) can make some fungal infections fluoresce.
• KOH (potassium hydroxide) preparation of skin scrapings: KOH dissolves skin cells leaving fungal elements visible under the microscope.
• Fungal culture or skin biopsy for difficult or atypical cases to identify the organism and guide treatment.

Treatment

• Topical antifungals (for example miconazole or terbinafine creams) applied as directed are effective for most superficial infections.
• Oral antifungals (such as griseofulvin, terbinafine or itraconazole) may be required for scalp or nail infections or extensive disease.
• For serious systemic fungal infections (different from superficial ringworm) intravenous antifungals such as amphotericin B are used under specialist care; amphotericin B is not a treatment for routine superficial dermatophytosis.
• Adjunct measures: keep affected areas dry, use talcum powder to reduce moisture, and avoid sharing personal items.

Prevention

• Maintain personal and household hygiene; wash hands after handling pets.
• Keep skin dry, wear breathable clothing and change damp garments promptly.
• Do not share personal items (combs, towels, footwear).
• Clean and dry communal bathing areas and avoid walking barefoot in public locker rooms.

Ringworm is usually not life-threatening but indicates the need for improved hygiene and, where necessary, medical treatment to prevent spread.

Dengue

Overview and historical notes: Dengue is a mosquito-borne viral illness common in tropical and subtropical regions. The reference records an early occurrence in India in 1780 (Chennai) and a notable epidemic in Kolkata in 1963-1964. All age groups are susceptible, and severe disease is more likely in infants, elderly and those with weak immune systems.

Causative agent and vector

• Dengue is caused by dengue viruses (four closely related serotypes: DENV-1 to DENV-4).
• The primary vector is the female mosquito Aedes aegypti, which bites mainly during the day and breeds in small collections of stagnant water.

Incubation and symptoms

• Symptoms most commonly appear 4-10 days after the bite of an infected mosquito (often noted 6-10 days in many descriptions).
• Fever of sudden onset, severe headache, retro-orbital pain (pain behind the eyes), severe joint and muscle pain, nausea, vomiting, rash and marked fatigue.
• Some patients develop mild bleeding (nosebleed, gum bleeding) or bruising.
• Severe dengue (dengue haemorrhagic fever/dengue shock syndrome) includes plasma leakage, severe bleeding and organ dysfunction and requires urgent medical care.

Transmission dynamics

• A mosquito becomes infected by biting a person who has dengue virus in their blood; after an incubation period in the mosquito the virus can be transmitted to another person when the mosquito feeds again.
• Dengue is not spread directly from person to person except rarely via blood transfusion or vertical transmission; the main route is through an infected mosquito vector.
• The reference explains vectors broadly: arthropods such as mosquitoes and ticks are common biological carriers of human pathogens.

Prevention and control

• Vector control: remove stagnant water that serves as breeding sites (discard containers, clean water storage), use larvicides where needed, and community-level environmental management.
• Personal protection: mosquito repellents, wearing long sleeves, using window screens and mosquito nets where appropriate; Aedes aegypti bites mainly during the day so protection during daylight matters.
• Early diagnosis and supportive medical care reduce the risk of complications.
• Some dengue vaccines exist with specific use recommendations; public-health authorities advise vaccine use based on local epidemiology and individual risk factors.

Chikungunya

What is Chikungunya? Chikungunya is a viral disease transmitted by infected mosquitoes, notably Aedes species. It occurs in Africa, Asia, India and other regions, and outbreaks have been reported worldwide.

Transmission

• Transmitted primarily through the bite of an infected mosquito.
• Outbreaks can spread to new areas through infected travellers who are bitten by local mosquitoes that then transmit the virus to other people.

Incubation and symptoms

• Symptoms typically appear 3-7 days after the infected mosquito bite.
• The most common symptoms are sudden high fever and severe joint pain (arthralgia), which may be debilitating.
• Other symptoms include muscle pain, headache, joint swelling and skin rash.
• Most patients recover within a week, but joint pain can persist for months in some cases.
• Severe disease is uncommon but infants infected around birth, older adults and people with underlying medical conditions may be at higher risk of complications.
• Infection usually confers long-lasting immunity to that chikungunya virus strain.

Management and prevention

• Treatment is supportive: rest, fluids, analgesics and anti-inflammatory drugs to relieve joint pain; severe cases need specialist care.
• Prevention focuses on mosquito control and personal protection (similar measures to dengue control).

Final note: Many common human diseases are preventable by basic public-health measures: safe water, improved sanitation, good personal hygiene, vaccination where available, early diagnosis and appropriate treatment. Understanding the causative agent, route of transmission and risk factors helps in effective prevention and control.