Protozoans

(AMOEBAS VOICE)

Amoebas belong to the group Sarcodina and are divided based on their motility and life cycles. Here, we focus specifically on those that infect humans, particularly in the United States, while recognizing there are many protozoan parasites that exist primarily in equatorial regions.

1. Entamoeba histolytica

• Primary Host: Humans

• Transmission: Ingestion through contaminated food, water, or surfaces that have come into contact with the amoeba.

• Prevalence: About 10% of the world population is infected, with 90% remaining asymptomatic.

• Symptoms: Individuals who grew up in endemic areas may experience initial symptoms but often become asymptomatic as adults.

  • Dysentery

  • Abdominal pain

  • Fever

  • Diarrhea

  • Weight loss

• Complications: Diarrhea can lead to dehydration, potentially resulting in death. Other complications may include bowel hemorrhaging, perforation, appendicitis, and tumor-like growths.

• Treatment: Antibiotics are effective against this infection.

2. Amoebic Infections of the Brain

• Common Types: Naegleria fowleri and Acanthamoeba

2.1 Naegleria fowleri

• Transmission: Acquired through nasal contact with contaminated water or traumatic eye damage.

• Symptoms: Causes primary acute meningoencephalitis, which can be fatal once it infiltrates the brain.

• Outcomes: Frequently reported cases in media, especially during summer; infections often lead to death. Rare survivals have occurred with new treatments.

2.2 Acanthamoeba

• Transmission: Often associated with contact lens wearers who may inadvertently use contaminated tap water to clean lenses.

• Symptoms: Can cause severe eye infections (keratitis) impacting the cornea and potentially leading to the destruction of the optic nerve, which is directly connected to the brain.

Environmental Factors

Both Naegleria and Acanthamoeba are present in standing water and can proliferate in warm conditions, particularly during droughts which concentrate their populations. The increase in temperature and decreased water volume aids in their reproduction, thus elevating the risks to individuals, particularly children, who may come into contact with such water during outdoor activities.

(CILIATES AND APICOMLEXA)

Ciliates and Apicomplexa are two groups of protozoa, each with unique characteristics and health implications.

Ciliates

Ciliates are not major pathogens but one notable member is Balantidium coli, which poses health concerns.

• Primary Host: Domestic animals, particularly pigs.

• Transmission: Ingestion of food or water contaminated with cysts from feces, often through poor hygiene practices.

• Symptoms: Can lead to intestinal symptoms including:

  • Erosion of the intestines

  • Diarrhea

  • Abdominal pain

  • Symptoms are rare among healthy individuals and even less common in those who are not healthy due to low exposure rates.

• Complications: Rarely penetrates the intestine or enters the bloodstream.

• Treatment: Effective antibiotics are available.

Apicomplexa (Sporozoans)

Apicomplexa have complex life cycles. As obligate parasites, mature forms lack means of movement such as flagella or cilia. They alternate between sexual and asexual phases and can switch hosts.
Key members include Plasmodium and Toxoplasma.

Plasmodium (Malaria)

• Pathogen: Plasmodium species are the causative agents of malaria.

• Transmission:

  • Primarily through the bite of infected female Anopheles mosquitoes.

  • Also transmitted through blood transfusions and from mother to fetus.

• Prevalence: Annually, there are 300-500 million new cases and approximately 2 million deaths, predominantly affecting children.

• Major Species:

  • Plasmodium falciparum is the most severe and responsible for the highest mortality rates.

• Symptoms:

  • Cyclic episodes of chills, fever, sweating, anemia, and organ enlargement. Symptoms can vary depending on the species involved.

• Diagnosis: Detection of trophozoites in red blood cells via blood smear.

• Treatment:

  • Historically used quinine, now there are multiple derivatives but rising drug resistance is a concern, especially for Plasmodium falciparum.

  • Some effective treatments are derived from plants, but their cost can be prohibitive in low-income countries.

Toxoplasma gondii

• Transmission: Acquired through ingestion of raw meat or contaminated surfaces (often associated with cat feces).

• Symptoms:

  • Most infections are asymptomatic but can have severe effects on fetuses, including complications such as birth defects or fetal demise.

• Prevalence: Common in urban environments with pet cats, but exposure is generally low unless cleaning litter boxes.

• Treatment: Options are available but can have side effects due to targeting eukaryotic cells.

Other Coccidian Parasites

• Babesia is notable for being the first protozoan linked to a vector (ticks) and causes red water fever in cattle, resembling malaria presentations.

• Medical professionals should be aware that infections resembling malaria may often be due to other causes, emphasizing the importance of accurate diagnosis based on patient history and potential exposure

(FLAGELLATES VOICE)

Flagellates, categorized under the group Mastigophora, are protozoans characterized by their flagella, which facilitate their movement. Here is an overview of notable flagellates that infect humans:

1. Trichomonas vaginalis

   • Characteristics: Small, pear-shaped organism with four anterior flagella and an undulating membrane; exists only in a trophozoite form (the actively feeding stage).

   • Infection: It is a leading sexually transmitted infection (STI) known as trichomoniasis.

   • Reservoir: Human urogenital tract.

   • Asymptomatic Cases: About 50% of those infected show no symptoms, which contributes to its spread.

   • Prevalence: Approximately 3 million cases per year.

   • Symptoms: Vary between males and females but tend to be pronounced in affected individuals.

   • Treatment: Antibiotics are effective, but the asymptomatic nature poses a concern for transmission.

2. Giardia lamblia

   • Characteristics: A protozoan parasite found in contaminated water, easily recognizable due to its unique heart-shaped appearance and concave ventral surface.

   • Transmission: Exposure occurs through drinking contaminated water or washing food with such water. Commonly found in environment such as ponds.

   • Reservoirs: Beavers, cattle, coyotes, cats, and humans.

   • Cyst Survival: Cysts can survive for an extended period in the environment, thus posing a risk.

   • Symptoms: Symptoms may include diarrhea and abdominal discomfort.

   • Treatment: Antibiotics are effective in treating the infections.

3. Hemoflagellates

   • Overview: These are blood flagellates that inhabit the bloodstream and tissues of human hosts and can cause severe and debilitating diseases. They are spread by blood-sucking insects that act as intermediate hosts.

   • Notable Species:

     • Trypanosoma cruzi

     • Disease: Causes Chagas disease, endemic to Central and South America; recent concerns arise from reported cases in southern Texas.

     • Transmission: Spread by the kissing bug (a type of reduviid bug) that takes blood meals from humans, often around the mouth at night.

     • Symptoms: Local lesions, fever, swelling of spleen and liver, potential heart complications due to chronic inflammation.

     • Treatment: Early treatment can lead to a cure; however, if diagnosed late, it may only be manageable.

4. Miscellaneous Information:

   • Awareness of blood flagellates is crucial as they can be life-threatening and are often linked to tropical regions where blood-sucking insects are prevalent.

   • Recognition of protozoan life cycles and their varying phases is essential for diagnosis and treatment.

(DNA viruses VOICE)

Introduction:
A variety of viruses infect humans, and this overview focuses on DNA viruses, organized by the Baltimore classification system—differentiated based on genetic material and whether they are enveloped or non-enveloped.

General Characteristics of DNA Viruses:

• Strandedness: Most DNA viruses are double-stranded, with the notable exception being Parvovirus, which is single-stranded. Hepatitis B is a unique case as it contains both double and single-stranded DNA but is classified among double-stranded viruses.

• Specificity: Viruses show various levels of specificity to hosts or cell types, which can range from general to highly specific. For example, Hepatitis B specifically infects human liver cells.

• Replication: Most DNA viruses bud off from the nucleus, leveraging nuclear machinery for replication.

• Infection Severity: Viral infections can range from asymptomatic to severe, with the potential for fatal outcomes.

• Zoonotic Nature: Some viruses can be transmitted from animals to humans (zoonoses).

DNA Virus Families:

There are seven DNA families causing human disease categorized as:

1. Enveloped DNA Viruses

2. Non-Enveloped DNA Viruses

3. Single-Stranded DNA Viruses

Pox Viruses:

• Examples: Variola (smallpox), monkeypox, cowpox.

• Characteristics: Pox viruses target the skin, causing lesions or pustules.

• Transmission: Monkeypox can cause skin pox, fever, and swollen lymph nodes. Cowpox typically infects the skin on hands, primarily through interactions with cows during milking.

• Historical Note: Smallpox was declared eradicated in 1977, leading to the cessation of inoculations in the U.S. as of 1971, though specific high-risk individuals may still receive vaccinations.

Herpes Viruses:

• Family: Includes Herpes Simplex Viruses 1 (HSV-1) and 2 (HSV-2), varicella-zoster virus (chickenpox and shingles).

• Characteristics: Large envelope viruses that can remain latent in the host, leading to recurrent infections.

• Transmission: HSV-1 typically causes oral lesions and is primarily contracted in childhood, whereas HSV-2 is sexually transmitted, mostly affecting adolescents and adults.

• Reactivation Triggers: Induced by factors like stress, sunshine (UV exposure), and mechanical injury, leading to outbreaks at locations depending on the nerve involved.

• Chickenpox/Shingles: Varicella-zoster is a herpes virus that leads to chickenpox upon initial exposure and can reactivate as shingles in older or immunocompromised patients.

• Caution: Shingles often follows dermatome patterns, caused by the reactivation of the dormant virus in neurons.

Epstein-Barr Virus (EBV):

• Transmission: Spread via oral contact and saliva, commonly linked to infectious mononucleosis.

• Prevalence: Most individuals are infected by midlife, some asymptomatic.

• Complications: Immunocompromised individuals are at risk for reactivating EBV infections.

Hepatitis Viruses:

• Overview: Hepatitis refers to liver inflammation caused by several different viruses; here we focus on Hepatitis B (hepadnavirus).

• Characteristics: Hepatitis B is an enveloped DNA virus with both single-stranded and double-stranded components, specifically infecting liver cells. It can lead to jaundice and chronic infections.

• Transmission Routes: Includes blood and bodily fluids, sexually transmitted, and can increase liver cancer risk.

Non-Enveloped DNA Viruses:

1. Papillomavirus (HPV):

   • Often associated with warts and certain cancers, especially cervical cancer. Two HPV types are primarily linked to cancer risk, vaccine development focuses on these high-risk types.

   • Transmission can occur through non-sexual means, with known types categorized by the lesions they cause (seed warts, plantar warts, genital warts).

2. Parvovirus:

   • Identified as B19 virus, known for causing fifth disease or slapped cheek syndrome, mainly in children.

   • Severe complications can occur if transmitted from pregnant women to fetuses, leading to anemia.

Conclusion:

Understanding the wide range of DNA viruses, their transmission methods, clinical implications, and treatment approaches is vital in infectious disease management. Familiarity with their characteristics facilitates better diagnostic and therapeutic strategies.

(RNA viruses)

RNA viruses encompass a larger group of pathogenic viruses and display significant diversity. There are 12 families categorized based on envelope, capsid structure, and RNA type.

1. Orthomyxoviruses

Influenza Viruses

• Types: Influenza A, B, C.

• Subtypes of Influenza A: H1N1 (swine flu, 1918 pandemic), H2N2, H3N2.

• Key Characteristics:

  • Hemagglutinin (H): 15 types, crucial for the virus's ability to bind to host cells.

  • Neuraminidase (N): Assists in virus release and prevents mucus trapping.

Infection Cycle

• Infection Site: Targets cells in the respiratory tract.

• Genome Behavior: Influenza virus is unusual as RNA genome segments enter the nucleus.

• Budding Process: Budding off the host cell incorporates cell membrane into the virus envelope, embedded with spikes.

Antigenic Factors

• Antigenic Drift: Gradual genetic changes in influenza B and C.

• Antigenic Shift: Rapid changes in influenza A due to RNA recombination in animal hosts.

2. Impact of Influenza

• Mortality: Influenza is a top 10 cause of death in the U.S., often leading to pneumonia as a secondary infection.

• Symptoms: Fever, chills, myalgia (muscle pain), sore throat, shortness of breath, cough, and lethargy.

3. Diagnosis and Treatment

• The diagnosis may involve testing for the flu virus to assess vaccine effectiveness.

• Vaccine: Annual trivalent vaccine recommended.

4. Bunyaviruses

Example: Hantavirus

• Characteristics: Zoonotic, with high mortality rate (33%) associated with pulmonary failure and high fever.

• Incidence: Occurs in specific geographic areas, particularly in the southwestern U.S.

5. Paramyxoviruses

• Characteristics: Sensitive viruses that can fuse with adjacent host cells (syncytia formation).

• Examples:

  • Morbillivirus: Causes measles; extremely contagious, with a single virus infectious dose.

  • Mumps: Painful swelling of parotid glands; vaccination is effective.

  • Respiratory Syncytial Virus (RSV): Major cause of respiratory infections in young children.

6. Rhabdovirus

• Example: Rabies

• Transmission: Through bites or scratches from infected mammals.

• Symptoms: Initial fever, progressing to agitation, seizures, and hydrophobia, leading to coma and death.

7. Coronaviruses

• Types: Includes SARS and MERS, causing significant respiratory illness.

• Symptoms: Fever, body aches, respiratory distress.

• Recent Notable Virus: SARS-CoV-2 (COVID-19).

8. Rubella (German Measles)

• Transmission: Through respiratory secretions.

• Vaccination: Part of the MMR vaccine (measles, mumps, rubella).

9. Hepatitis C Virus

• Characteristics: RNA virus, acquired through blood contact.

• Chronic Infection: 75-85% will develop chronic infection; severe symptoms can lead to liver cancer.

10. Arboviruses

• Definition: Insect-borne viruses, including Colorado Tick Fever.

• Transmission: Primarily through ticks, with various symptoms depending on the virus.

Understanding the diversity and impact of RNA viruses is critical for effective diagnosis and treatment of viral infections, emphasizing the need for ongoing research and public health awareness.

There are several viral infections that have significant implications for public health, particularly in the context of arboviruses and their transmission through mosquitoes.

1. Encephalitis Viruses

   • Western Equine Encephalitis

   • Eastern Equine Encephalitis

   • California Encephalitis

   • St. Louis Encephalitis

   • West Nile Encephalitis: The resurgence of these diseases has been largely affected by past DDT spraying campaigns, which drastically reduced mosquito populations until its cessation. As mosquito populations recover, these diseases are becoming more prevalent.

2. Yellow Fever

   • Also known as "vomiting negra" due to the presence of black vomit containing blood.

   • Transmission: Urban (human to mosquito to human) and Sylvan (monkey to mosquito to human).

   • Symptoms: Acute fever, headache, muscle pain, oral hemorrhage, jaundice, liver and kidney damage, high mortality rate.

   • Historical Insight: Early theories of transmission were incorrect until physicians utilized self-experimentation to uncover the role of mosquitoes.

3. Dengue Fever

   • Caused by the flavivirus and typically transmitted by mosquitos.

   • Symptoms: Mild or severe (dengue hemorrhagic fever syndrome, breakbone fever). Recent cases have been documented in Florida.

4. HIV/AIDS

   • HIV (Human Immunodeficiency Virus) is distinct from AIDS (Acquired Immunodeficiency Syndrome), which it causes.

   • Characteristics: Retrovirus that integrates into host DNA, primarily infecting CD4+ T cells through specific cellular receptors.

   • Transmission: Occurs through sexual contact, blood transfusions, IV drug use, or from mother to infant.

   • Pathogenesis: After initial infection, HIV targets macrophages and T cells, leading to immune system degradation. Symptoms may present after years of latent infection, depending on CD4 counts.

   • Diagnosis: Based on the presence of virus and/or a reduced CD4 count or through opportunistic infections. Patients may exhibit initial flu-like symptoms before progressing to severe complications.

5. Non-Envelope Non-Segmented RNA Viruses

   • Poliovirus: Infects through the fecal-oral route, causing acute neuromuscular paralysis.

   • Hepatitis A: Infectious hepatitis primarily transmitted via food. Most cases are acute, with the likelihood of recovery.

   • Rhinovirus: Common cause of colds, highly transmissible in acidic environments, specifically infects the nose due to optimal temperatures for replication.

   • Norovirus: Known as the Norwalk agent, accounts for a significant proportion of viral gastroenteritis cases with rapid recovery supported through therapy.

Understanding the various viral infections, their transmission routes, and the symptoms they present is vital for effective diagnosis and treatment in public health scenarios.