Microbio590S Lecture 2: Terms and Parasitology Concepts – Example of re- emerging neglected disease
Michele Klingbeil Office: Morrill IVN Room 222 By appointment only [email protected]
Symbiosis
“living together” • Intimate association between two different species – Usually a larger organism is the host, the smaller is the symbiont
• Give some examples of symbioses
Specific types of association
Phoresis - Traveling Together
• No dependence from either participant
• One participant is usually machanically carried by the other
• Hitch-hiking
Crab + Barnacle Commensalism
• “Sharing at the table”
• One partner benefits, but the other is neither helped nor harmed.
Clownfish + Sea anemone
Mutualism
Endosymbiosis - mitochondria
• Interspecific interaction that benefits both members
• Frequently, the relationship Lichen on tree bark is essential for survival of at least one of the members – Obligate interaction
Moray + cleaner wrasse
Parasitism
• Parasite and parasitism
are terms that define a Phoresis and way of life rather than a Commensalism coherent evolutionary related group of
organisms. Parasitism Mutualism
• Numerous definitions – the intimate association of two species where one species (the parasite) benefits at the expense of the other (the host). – the parasite relies on the host for nutrients and as a place to live. Is this Parasitism?
• The benefit in these relationships are clearly skewed toward the lion and the spider.
• Predator vs. prey • Predators tend to be larger than their prey, and consume many prey in a lifetime.
What is a Parasite?
• Parasites are usually much smaller than their host, and do not kill the host before taking a meal.
Is This Parasitism?
• Micropredation - the mosquito is certainly gaining a nice blood meal.
• Blurry lines between these definitions.
• The host is the food source, and a specific niche for the parasite.
• Many parasites show strict specificity for a single host species. Parasite Diversity!
Parasitology as a scientific discipline historically covers a diverse collection of multi- and unicellular eukaryotic organisms Protozoa: unicellular eukaryotes (this is a historic term, protozoans are not really a monophyletic group) Platyhelminthes: flatworms these include flukes and tape worms Nematodes: elongated worms with rigid cuticule Arthropodes: insects, ticks and mites which either are parasitic or transmit parasites as vectors (we only have time to discuss the most important groups causing human and some animal disease, there are many additional parasites outside these groups)
Parasite Diversity!
• Not a phylogenetically related group of organisms
– Single celled eukaryotes - Protists (protozoa) – Mutlicellular worms - Helminths
• Many are Vector transmitted disases
• Zoonoses - transmission of the infectious agent to humans from an animal reservoir. No establishment of a permanent new life cycle solely in humans (still requires animals). Ecto- vs Endoparasites
• Ectoparasites live on, but not in their hosts. Protozoan Ichthyophthirius that causes fish “Ick”
Endoparasites live within the body and tissue of their hosts. The majority of parasites to be discussed. Protozoan Trypanosoma that causes African Sleeping sickness.
Facultative vs. Obligate
• Facultative - usually a free-living organism but can invade host under certain conditions. Can cause Naegleria fowleri severe disease. Obligate - most parasites Trypanosoma cruzi require a host for at least one stage of its life cycle. Some parasitic worms have free-living larval stages.
Intermittent vs. Permanent
• Intermittent/ temporary - micropredation - “parasite” feeds on the host and then leaves.
• Permanent - parasite that lives its entire adult life on or within the host. Most of the parasites we discuss are permanent. Life Cycles
Entamoeba histolytica • Direct Life Cycle - parasite passes from one host to the next through contaminated food/water, air, or sexual intercourse.
Indirect Life Cycle - parasite passes from one host to the next through a vector and/ Diphyllobothrium or intermediate host. Many latum parasites have complex indirect life cycles.
Vectors for Transmission Vectors - Actively transmit parasites
• Mechanical Vector - no multiplication or development of parasite takes place. Horse fly
• Biological Vector - Tsetse fly either multiplication or development takes place.
Transmission of 2 related parasites
Tsetse fly
Horse fly
• Feeds often moving • Proboscus used for front legs and mouth blood meal - longer parts vigorously. feeding period. – Trypanosoma brucei – Trypanosoma evansi bloodstream form is remains on the ingested - develop to mouth parts - no procyclic form - migrate biological and develop to infective development occurs. epimastigotes (new form). Host Definitions
• Definitive host - where sexual reproduction occurs. If there is no sexual reproduction documented, then it is the host that is most important to humans. – Typically a vertebrate. Exception - Plasmodium • Intermediate host - where asexual replication or parasite development occurs. • Paratenic host - transport host, but parasites do not develop in this host. • Reservoir host - any animal that carries an infection that can serve as a source of infection to human and other animals. • Accidental host - parasite enters or attaches to other than the normal host. Parasites usually do not survive in the wrong host, but can cause serious disease (Toxocara).
Life Cycle Example
Intermediate Paratenic Bridging the gap between human Host Host And small fish/copepod.
Copepod Monoecious Intermediate Hermaphroditic Host Definitive Diphyllobothrium Host latum
Free-swimming stage
Summary of Introduction
commensalism, mutualism, parasitism, ecto, endo, obligate, facultative, intermittent parasitism …) Hosts (final, intermediate, paratenic, accidental, reservoir …) Disease terminology (infection, infestation, acute, chronic, patency, incubation period, crisis, convalescence …) Parasites Among Us
“…no matter how we set ourselves off from nature we remain a part of it, and thus we invariably share parasites with the other species in which we live.”
Julius P. Kreier PARASITIC PROTOZOA
Emerging Infectious Disease
Infectious diseases whose incidence in humans has increased in the past 2 decades or threatens to increase in the near future have been defined as "emerging." These diseases respect no national boundaries include:
New infections resulting from changes or evolution of existing organisms (host and/or pathogen)
Known infections spreading to new geographic areas or populations
Previously unrecognized infections appearing in areas undergoing ecologic transformation
Old infections re-emerging as a result of antimicrobial resistance for known agents or breakdowns in public health measures.
Emerging(re) Infectious Disease
-HIV Species Jumping -Influenza -Hepatitis C and E
-E. coli 0157:H7 -Cryptosporidium -Ebola -Hantavirus Zoonoses -Lyme disease -nvCJD -Trypanosomiasis -West Nile Virus Zoonoses
Zoonoses - transmission of the infectious agent to humans from an animal reservoir. No establishment of a permanent new life cycle solely in humans (still requires animals).
Species jumping - the infectious agent derives from an ancient animal reservoir, but has established a new life cycle in humans that DOES NOT require an animal transmission phase any longer.
Contributing Factors for Zoonoses
Pathogen evolution (adaptation)
Host condition
Vaccination
Immunological disorders
Host population
Urban crowding (land use)
Host demographics & behavior
Global travel
Environmental
Climate
Destruction
Public Health breakdown
Dealing with Zoonoses
Why are the pathogens jumping? Can we predict this?
Who will be the world’s doctor? WHO, UN - need to get rid of political links?
Who will be the world’s expert on zoonoses?
Develop new strategies to deal specifically with emerging zoonoses.
Surveillance will be key, but also greater involvement of field and basic science research. Numbers of People with Parasitic Diseases
Disease with HIGH morbidity Disease with HIGH mortality: and QL losses:
– Malaria - 489 M – Schistosomiasis - 200 M – Sleeping Sickness 0.5 M – Onchocerciasis - 37 M – Filiariasis - 350 M – Chagas disease - 18 M – Ascariasis – 807 M – Visceral Leishmaniasis - 4 M – Hookworm diseases – 600 M – Trichuriasis – 605 M – Cutaneous leishmaniasis - 8 M – Food and waterborne Estimated World Pop by UN protozoan - 1.5 B 10/31/11 7 Billion
Human African Trypanosomiasis
• Classical example of a zoonotic emerging infection, 1890-1930.
• Leading public health problem in Africa at that time, colonialism brought the disease to new areas with a 2/3 death rate.
• Nearly eliminated by 1960 using population screening, case treatment, chemoprophylaxis, and vector control.
• Currently classified by WHO as a re-emerging and uncontrolled disease.
HATHAT Nearly Nearly Eliminated Eliminated in in 1960s 1960!
Human African Trypanosomiasis, central Africa, 1926-1999
HAT: re-emerging, Neglected Tropical Disease How Was Control Successful?
……..and now
Anion Exchange Card agglutination Test Molecular Tools Centrifugation Technique
Time consuming Sensitive Expensive Still under development Additional equipment
Large # of false +’s
Estimating Disease Burden
> 60 M people at risk, only about 3-6 M are screened for HAT.
Health facilities lacking in disease foci areas.
Little if any public health measures being implemented.
Huge political conflict and insecurity in epidemic foci.
Clinical diagnosis is difficult until late stage. Intermittent fever - malaria? Weight lose - AIDS? Diagnostics - false negatives Barriers to Control HAT
Insufficient resources - developing countries
War and civil disturbances = refugees
No vaccine = no prevention
Crisis in chemotherapeutics
Melarsoprol was 95% effective, but in 1997 resistance up to 30% was emerging in Uganda, Sudan and Angola (DRofC little data).
Arsenal of therapeutic drugs is minimal (~6)
Toxicity - drugs kill 4-10% of the patients.
Do you know these public health workers? • World’s first peer-reviewed, open-access journal devoted to the NTDs
• Launch supported by Bill and Melinda Gates Foundation
• Papers on pathology, epidemiology, treatment, control, prevention • Magazine section devoted to policy and advocacy • International editorial board—half of the Associate Editors are from endemic countries
“It is expected that the journal will be both catalytic and transformative in promoting science, policy, and advocacy for these diseases of the poor.” —Peter Hotez, Editor-in-Chief