Parasite/Host Relationships Copyright 2011 PEER.tamu.edu

What is a HOST? What is a PARASITE?  Before we even begin, I want each student to write down on a piece of paper what they think a HOST is and what they think a PARASITE is. 1-2 minutes, GO!  After you have written down your thoughts, fold your paper and trade it with someone else who is done in the class. 30 seconds, GO!

NEXT:  Read your piece of paper, if you think your paper has a correct answer raise your hand and read it out loud.  If it is correct, you and the person who wrote the answer will receive *___ pts on your next quiz.

Final Answer (Should go something like this)  A HOST is any organism that another organism or bacteria live in or on.  The PARASITE is the organism living inside (endoparasite) or on (ectoparasite) the HOST. This means the parasite benefits at the expense of the host. The host-parasite relationship is typically species specific. *Lets think about and discuss some examples of a parasite/host relationship

Some Examples:

Common Types of Parasites:  Think fast! You have one minute to list as many parasites as you can. Remember to include what species they affect.

Parasite Life Cycle:  The life cycle is a never-ending chain of events that lead to the parasite constantly reproducing and re-infesting another animal.  There are two types of lifecycles: Indirect - require different types of hosts or a vector (intermediate host) for various stages of their life cycle. Direct - a life cycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector of another species.

The Intermediate Host  Required by some parasites to complete their life cycle,  Advantages of an intermediate hosts include: increasing the spread of the parasite & protecting the parasite from spending too much time in the environment.  What is the intermediate host in the life cycle of the Heartworm?

Why do I need to know this?  Take a moment to explain to a neighbor the importance of understanding life cycles of common parasites. Hint: think about controlling and preventing disease.

Importance of Life Cycles  Understanding the life cycle of a parasite provides valuable information concerning: The individual infested How the particular stage in the life cycle affects the host The most common time of year for the parasite to be in the environment Types of infestation/sickness caused by the organism Vulnerable points in the life cycle for the best treatment and prevention

Think It Through  The next two slides show diagrams and descriptions of two different parasite lifecycles.  Determine whether the depicted lifecycle is direct or indirect and give justification for your answer.

Liver Fluke Life Cycle

Your Turn – Complete The Life Cycle 5. Infected adult flea ingested by dog Eggs ingested by larval flea Segments of adult worm passed in feces Adult worms develop in small intestine Segments & egg packets in feces & on fur Larval flea develops into adult flea and contains immature tapeworm

Parasite Transmission  Examine the images and determine how a parasite might gain access to the host.

Diagnosis  Why is a fecal examination a useful tool to diagnose a large variety of parasites?  What other methods might be used to make a diagnosis?

Treatment  Why take the time to diagnose a parasite? Can’t we just give an animal medicine to kill any parasite they might have?

Drug Resistance  Multiple species of parasites have developed resistance to many treatments. Parasites with genomes that allow them to survive treatment can pass this DNA to their offspring. Thus, in following generations, the whole population becomes resistant.

Potential Side-effects  Often times parasites and their hosts have similarities that may make the treatment drug harmful to the host as well. Example: the only proven method to kill adult heartworms in the dog is to use arsenic, a highly toxic compound that is potentially deadly to the host (dog) as well.

Treatment  Administer drugs strategically  Focus on prevention

Large Animal Case Study  Dr. Brown was called to Ag farm to examine Scout, a 1000 pound Thoroughbred. Scout is unable to put on weight and has a dull, coarse coat. A fecal exam reveals large strongyle and ascarid eggs. Dr. Brown recommends a broad spectrum anti-parasitic given at 1 mg per 5 kg of body weight. What dose should Scout be given? Don’t forget to convert from pounds to kilograms!

Prevention  View the images below & identify management practices that could lead to parasite infestation

Prevention  Over-crowding, over-grazing, and poor sanitary conditions lead to increased exposure to parasite eggs and a greater degree of infestation.  Pasture management (mowing, rotation, etc…) exposes eggs & larvae reducing their chance of survival.  Parasites can't survive indefinitely outside of a host and at some point they must invade the primary host in order to sustain the cycle.

Research in Parasite Treatment  New Drugs Constant need for new drugs for resistant parasites  Common problem with fleas. Companies are coming out with new products every few years because the old products are ineffective Special concerns with drugs given to food producing animals because of potential accumulation of drugs in tissues for human consumption  Animal Research Many parasites are host specific, testing can only be done in susceptible species. Even if a parasite infects different species, it often behaves differently in the different hosts

Research in Parasite Treatment  Vaccines limited success Parasites have complex antigens that are difficult to characterize Vaccine research is expensive and it is difficult to get funding There are some new vaccines for parasites on the horizon but only time will tell if these prove to be effective treatments

References  arasitelists/pdlist.html arasitelists/pdlist.html    ogyPages/S/Symbiosis.html ogyPages/S/Symbiosis.html  &aid=757 &aid=757