Lecture 13 - Helminths, Arthropods and Animal Borne Infectious Diseases

Lecture 13: Helminths, Arthropods, and Animal-Borne Infectious Diseases

Introduction

  • Focus on the diverse microbial eukaryotic infectious agents, specifically:

    • Helminths

    • Arthropods

    • Animal-borne pathogens

  • Course: BIO-242-01 World Disease

  • Instructor: Qasim Beg, PhD

Diversity of Microbial Eukaryotic Infectious Agents

Helminths

  • Nematodes (Roundworms)

    • Description: Cylindrical shape, hence the term "roundworm".

    • Digestive system: Digestive tube with an anus.

  • Trematodes (Flukes)

    • Description: Oval-shaped flatworms with an internal digestive tube ending in a cecum (no anus).

    • Characteristics: Hermaphroditic (both male and female reproductive structures).

  • Cestodes (Tapeworms)

    • Description: Parasitic flatworms that absorb nutrients through their skin.

    • Structure: Composed of a head (scolex) and a series of segments (proglottids) containing reproductive organs.

Diseases Caused by Helminths

How Helminths Cause Diseases

  • Mechanisms of Disease:

    • Feeding on host tissues leading to:

    • Blood loss (anemia)

    • Nutritional malabsorption

    • Tissue damage (affecting skin, lungs, liver, and intestines resulting in diarrhea and further blood loss)

    • Migrating through the body, resulting in:

    • Immune response triggered by migration

    • Symptoms include:

      • Edema (swelling)

      • Arthritis

      • Hypersensitivity reactions such as anaphylaxis

      • Inflammation and asthma when migrating through the lungs.

Nematodes

  • Pinworms (Enterobius vermicularis)

    • Small white nematodes.

  • Hookworms (Ancylostoma duodenale and Necator americanus)

    • Transmission: Larvae penetrate the skin and travel through the bloodstream to the lungs.

    • Lifecycle: Migrate to alveoli, causing coughing, then swallowed to the small intestine where they attach to the intestinal lining and suck blood. Offspring eliminated in host feces.

  • Roundworms (Ascaris lumbricoides)

    • Transmission: Eggs ingested from contaminated soil.

    • Pathology: Worms grow significantly in size within the digestive tract and can invade lungs or other organs causing serious damage.

Trematodes (Flukes)

  • Structure:

    • Possess internalized mouth, pharynx, and a digestive tube ending in pouches called caeca (no anus, requiring waste expulsion back through the mouth).

    • Typically have two suckers for attachment: one near the mouth and one on the ventral side.

Cestodes (Tapeworms)

  • Transmission: As larvae in uncooked meat (pork - Taenia solium, beef - Taenia saginata, and fish - Diphyllobothrium).

  • Growth: Can reach lengths of 2–15 meters depending on species.

Animal-Transmitted Pathogens

Zoonosis

  • Definition: An animal disease that can be transmitted to humans, typically via direct contact, aerosols, or bites.

  • Types of diseases in animals:

    • Enzootic: Present endemically in certain populations.

    • Epizootic: Incidental incidence reaching epidemic levels.

  • Examples include:

    • Rabies virus

    • Hanta virus

Rabies Virus (Rhabdovirus)

  • Nature: Infects the central nervous system of warm-blooded animals, can be fatal if untreated.

  • Transmission: Enters through bites from infected hosts.

  • Reservoirs in the U.S. include raccoons, skunks, coyotes, foxes, and bats.

  • Statistics: More than 50,000 fatalities annually worldwide, primarily in developing countries; over 1 million receive post-exposure prophylactic care.

  • Pathogenesis:

    • Symptoms: Fever, excitation, pupil dilation, excessive salivation, anxiety, fear of swallowing.

  • Diagnosis:

    • Techniques: Tissue samples through fluorescent monoclonal antibodies or RT-PCR.

    • Detection of Negri bodies through staining.

  • Treatment:

    • Vaccination post-bite.

Hantavirus

  • Nature: Part of the Bunyaviridae family, enveloped, segmented negative-strand RNA viruses.

  • Hosts: Infects rodents such as mice, rats, voles, and lemmings.

  • Transmission: Inhalation of virus-contaminated rodent excreta.

Hantavirus Pathogenesis

  • Disease forms:

    • Hantavirus pulmonary syndrome (HPS)

    • Hemorrhagic fever with renal syndrome (HFRS)

  • Characteristics:

    • HPS characterized by sudden onset of fever, myalgia, thrombocytopenia, leukocytosis, pulmonary capillary leakage, with approximately 35% mortality within days.

  • Diagnosis and Treatment:

    • Tests: Neutralization assays, RT-PCR.

    • Treatment: No specific antivirals, oxygen therapy recommended.

Arthropods and Transmitted Diseases

  • Description: Invertebrate animals with exoskeletons and jointed appendages. Some are free-living, while others are ectoparasites.

  • Vectors: May transmit infectious diseases through feeding.

Important Diseases by Arthropods

  • Mites:

    • Scabies: Caused by Sarcoptes scabiei; leads to burrowing into skin and egg laying.

  • Ticks:

    • Lyme disease (caused by Borrelia burgdorferi)

    • Rocky Mountain spotted fever (caused by Rickettsia rickettsii)

Apicomplexans

  • Description: Major group of parasites affecting humans and animals.

  • Apical Complex: Specialized structure facilitating parasite entry into host cells.

  • Major diseases include malaria (caused by Plasmodium spp.) and babesiosis (caused by Babesia, transmitted by ticks).

Rickettsial Pathogens

  • Characteristics: Small bacteria existing strictly within vertebrates (intracellular parasites).

  • Groups:

    • Typhus group: e.g., Rickettsia prowazekii

    • Spotted fever group: e.g., Rickettsia rickettsii

    • Ehrlichiosis group: e.g., Ehrlichia chaffeensis

Treatment and Prevention for Rickettsial Diseases

  • Diagnostic Techniques: Fluorescent antibody assays, PCR, ELISAs.

  • Preventative Measures: Control of vectors, insect repellents.

Lyme Disease

  • Most prevalent tick-borne disease in the U.S., caused by Borrelia burgdorferi.

  • Reservoirs: Deer and white-footed field mouse.

  • Symptoms: Headaches, fatigue, fever, chills, and in 75% of cases, a rash at the tick bite location.

Leishmaniasis

  • Caused by Leishmania donovani, transmitted by the bite of infected sandflies.

  • Forms: Cutaneous leishmaniasis and visceral leishmaniasis (more serious).

Flaviviruses

  • Examples: Yellow fever virus, Zika virus, Dengue virus, transmitted via mosquito or tick bites.

  • Notable diseases include:

    • Yellow fever: endemic to tropical regions; preventable via vaccination.

    • Dengue fever: symptomatically mild but widespread in endemic regions; vaccines recently approved.

Case Studies

Case Study: Leishmaniasis

  • Patient: Mario, a 29-year-old pizza delivery worker, develops sores after returning from tour in Iraq. Diagnosed with cutaneous leishmaniasis based on symptoms and confirmed via microscopy.

  • Treatment: Prescribed sodium stibogluconate, a mineral-based treatment effective against Leishmania.

Case Study: Pinworm Scenario

  • Patient: Dotty, a 2-year-old with symptoms consistent with pinworm infection. Diagnosed through a tape test confirming presence of pinworms and eggs.

  • Treatment: Mebendazole prescribed to the family to eradicate infection over time.

Summary

  • Understanding helminths, arthropods, and animal-borne infectious diseases is vital for preventing disease transmission and ensuring better public health outcomes. Awareness of symptoms, transmission methods, and available treatments can help mitigate these infections in both human and animal populations.