Microbes and Diseases

Chapter 01

THE “FLU”Influenza

Influenza

• Reasons to study “the flu”:– Annual flu seasons have the potential for turning

deadly for many people very quickly– Many diseases are erroneously termed “the flu”– Behavior of influenza viruses illustrates how

viruses can and do cause more serious diseases than they did previously

Etiology

• Influenza Virus• Segmented RNA virus– Allows for the virus to potentially change the

nature of its spike proteins…antigenic shift

Influenza Spike Proteins• Hemagglutinin:

– Has agglutinating action on red blood cells

– Binds to host cell receptors of respiratory mucosa

• Neuraminidase:– Breaks down protective mucus

coating of the respiratory tract– Assists viral budding and release– Keeps viruses from sticking

together– Participates in host cell fusion

Types of Flu Viruses

• H3N2 – most common human flu viruses• H1N1 – avian flu that can be spread to swine

and humans• H1N2 – a type of swine flu known to spread to

humans• H5N1 and H7N9 – virulent forms of avian flu

that pose a potential for human pandemic

Symptoms & Severity

• Headache, chills, dry cough, body aches, fever, stuffy nose, sore throat

• Extreme fatigue can last for a few days or weeks• H1N1 “Swine flu”: not all patients had a fever, many

patients had gastrointestinal distress, or developed multiorgan system failure

• Most patients recover within a few days to a couple of weeks

Epidemiology

• Transmitted by droplet contact– Sneezing, coughing, talking– Possibly by contact with surfaces handled by others

currently experiencing the flu

• People are infectious between 1 day before symptoms appear to 7+ days after becoming sick– Symptoms usually take 1 to 4 days to appear after virus

enters host

• Peak activity from December to March– “Flu” season

Prevention

• Stay home if sick or avoid sick people• Standard vaccine is 70 – 90% effective– Consists of three different inactivated influenza strains that

is updated annually– FluMist: contains three live, attenuated strains– Side effects can mimic flu-like symptoms

• Scientists are continually researching emerging strains to attempt to prevent a pandemic

Treatment

• Tamiflu® (oseltamivir) – pill or liquid– Prescribed for 5 days

• Relenza® (zanamivir) – inhaled powder– NOT recommended for people with COPD– Also prescribed for 5 days

• Rapivab® (peramivir) – intravenous only– Administered for 15-30 minutes

• Side effects exist for ALL treatments

PNEUMOCOCCAL PNEUMONIAStreptococcus pneumoniae

Pneumonia as a Disease

• Can be caused by a wide variety of microorganisms– Must be able to avoid phagocytosis– Or avoid killing once inside macrophages

• Other bacteria that cause pneumonia include Mycoplasma pneumoniae

• Viral pneumonia is usually (but not always) milder than bacterial pneumonia

• Fungi can also cause pneumonia– Most often in immunocompromised people

Etiology

• Streptococcus pneumoniae• Accounts for 40% of community-acquired cases• Small, gram-positive flattened coccus that appears in

pairs• Polysaccharide capsule prevents effective

phagocytosis– Blocks action of complement proteins– Causes inflammatory fluids to build up in the lung

Other Diseases Caused by S. pneumoniae

• Ear infections• Sinus infections• Meningitis• Bacteremia

• Streptococcus species cause more microbial diseases in humans than any other microbe

Risk Factors

• Children:– Under 2 years of age– In child care settings– Are immunocompromised by another infection– With cochlear implants

• Adults 19 – 64:– With underlying chronic illnesses– Are immunocompromised by another infection– In long-term living facilities (nursing homes)– With cochlear implants– Who smoke

• Adults over 65

Epidemiology

• Part of the normal biota of the respiratory tract• Infection occurs when bacterium inhaled into the

deep areas of the lung– Factors that enhance disease: old age, season, underlying

viral respiratory disease, diabetes, chronic abuse of alcohol or narcotics

• Transmission is through droplet contact with respiratory secretions

Symptoms & Complications• Begin with runny nose and

congestion, headache, and fever• Chest pain, fever, cough,

production of discolored sputum as it enters lungs

• Patient appears pale and sickly due to pain and difficulty breathing

• Severity and speed of onset of symptoms depend on the etiologic agent

Diagnosis & Treatment

• Inflammatory condition of the lung in which fluid fills the alveoli

• If invasive, blood samples or a spinal tap to collect cerebrospinal fluid (CSF) may be required– Often requires laboratory culturing of the bacteria

• If non-invasive, standard physical examination by clinician• Treated using “broad-spectrum” antibiotics

– Many strains of S. pneumoniae are resistant to penicillin and its derivatives, macrolides, tetracyclines, and fluoroquinolones

Prevention

• Pneumococcal conjugated vaccine (PCV13 or Prevnar 13®)– Recommended for adults over 19 with pre-existing medical

conditions– Vaccine is also encouraged for adults over 65

• Pneumococcal polysaccharide vaccine (PPSV23 or Pneumovax 23®)– Recommended for adults over 19 who smoke or have

asthma– Vaccine is also encouraged for adults over 65

PRIMARY AMOEBIC MENINGOENCEPHALITIS (PAM)

Naegleria fowleri

Meningoencephalitis

• Inflammation of the brain and spinal cord– Because of the close association of the brain and

spinal cord, infection of one structure may involve the other

Etiology

• Naegleria fowleri• Small, flask-shaped amoeba that moves by means of

a single pseudopod– Rounded, thick-walled uninucleate cyst that is resistant to

temperature extremes and mild chlorination

• Often found in warm freshwater and soil– Particularly problematic during hot, dry Florida summers in

our local, slow-moving waterways

Illness & Symptoms

• Cases are rare, but the disease advances so rapidly that treatment is futile– 3 in 132 cases in the US have survived

• Stage 1 – severe frontal headache, fever, nausea, and vomiting

• Stage 2 – stiff neck, seizures, altered mental state, hallucinations, and coma

Sources of Infection & Risk Factors• Infections reported in people who

have been swimming in warm, natural bodies of fresh water

• Amoebas forced into nasal passages utilize the olfactory nerve to enter the brain– Enters the subarachnoid space

causing primary amoebic meningoencephalitis (PAM)

– Causes rapid, massive destruction of brain and spinal tissue

Diagnosis & Detection

• Spinal tap of CSF often shows presence of the motile amoeba

• Polymerase Chain Reaction (PCR) can detect the presence of the DNA associated with the amoeba

• Amoeba can be cultured in the lab or detected in the water supply to increase effectiveness of the two methods

Treatment

• Traditionally, only supportive care has been given due to the rapid progression of the disease

• Miltefosine, an anti-cancer drug, has shown to have anti-amoebic effects when used with other drugs– This, along with therapeutic hyperthermia, is

thought to have saved a 12-year old girl in 2013

Prevention & Control

• Infection can only occur if the amoeba enters your nose– Drinking contaminated water has not been shown to lead

to infection

• Hold nose or use nose-clips when swimming in freshwater environments, avoid submerging your head in warm freshwater environments, avoid freshwater during very hot, dry seasons, avoid stirring up sediment in freshwater environments

ORAL CANDIDIASISCandida albicans

Etiology

• Candida albicans– Most common source of

human infections

• Dimorphic fungus

Sources of Infection

• Normal biota of 50 – 100% of humans– Mouth, GI tract, vagina

• Usually opportunistic infection due to disruption of the normal biota• Causes oral candidiasis within the mouth or vuvlovaginal

candidiasis in the vagina

Symptoms

• Redness or soreness at the site of infection• Difficulty swallowing• Cracks at the corners of the mouth (angular

cheilitis)

Risk Factors & Prevention

• Uncommon infection in healthy adults• Often affects immunocompromised individuals– HIV/AIDS, cancer,

• Also affects individuals with organ transplants, diabetes, dentures, or people using corticosteroids or broad-spectrum antibiotics

• Most easily prevented through good oral hygene• Using chlorhexidine mouthwash for people currently

suffering from oral thrush is effective

Diagnosis & Testing

• Easily detectable on a wet prep or gram stain• Grows in thick, curdlike colonies on the walls of the

vagina or throat

Treatment & Outcomes

• Clotrimazole troches or nystatin suspensions are often used to treat mild to moderate cases

• Fluconazole or itraconazole may be required for esophageal cases or cases that persist

• Amphoteracin B is required for severe or resistant cases

ENTEROBIASIS (PINWORM INFECTION)

Enterobius vermicularis

Etiology

• Enterobius verminularis• Helmenthic parasite

Epidemiology & Risk Factors

• Humans are only known reservoir for this parasite• Most common worm disease of children in

temperate zones• Transmission is through ingestion of the worm’s eggs

or indirectly through contact– Even possible to ingest while breathing– Hands, toys, bedding, clothing, toilet seats

Biology (Life Cycle)

• Female worms exit the anus and lay eggs at night

• Eggs are then ingested by new host starting a new cycle of infection

Symptoms or Signs

• Pronounced anal itching, abdominal discomfort, difficulty sleeping– Secondary infections may result from abrasions of the

perianal region from excessive scratching

• Infection is not fatal and most cases are asymptomatic– However, females may also experience infection of the

vaginal canal

Diagnosis & Detection

• Look for worms in perianal region 2 – 3 hours after the infected person is asleep

• Use transparent tape to collect eggs and examine using a microscope– Done on 3 consecutive mornings after person wakes

• Examine samples from fingernails under a microscope

Treatment

• Mebendazole, pyrantel pamoate,a nd albendazole– Given as one dose and then again as a single dose

2 weeks later– Does not reliable kill eggs, so second dose helps

prevent reinfection• Infections occurring in households should be treated

simultaneously among all members

Prevention

• Proper hand washing anytime after contact with the perianal region is the most effective way to prevent the infection

• Showering every morning, especially if recovering from an infection, is also effective

• Frequent changing of bedclothes among infected individuals is also recommended