By: Stavana Strutz 

So I'm going to talk about some parasites today that even Xzibit would be proud of: parasites carrying parasites. There are macroparasites and microparasites. Macroparasites are basically parasites you can see: ticks, helminths, lice, etc. They can be endoparasitic (within the host) or ectoparasitic (outside the host). Microparasites, such as  viruses, bacteria, fungi, and protozoa, require a microscope and are generally endoparasitic. 

There are also epiphytic plant parasites like mistletoe. I bring up this example to remind readers that plants also have to fight off ectoparasites and endoparasites. And then there are brood parasites like the cuckoo bird who lay eggs in other bird species' nests and parasitoid ichneumonid  wasps that lay eggs inside of caterpillars Alien-style. Both these organisms have portions of their life cycle that are not reliant on a host. I wanted to share the last three examples because they are not generally what people think of when initially imagining parasites. There is a huge amount of diversity when it comes to the free-loaders of the world.

Now that we've gone over some terminology, let's get to the theme of today's post. Two months ago at Nerd Nite near the very end of my talk I brought up the topic of recent outbreaks of murine typhus in central Texas. Murine typhus is a bacterial disease (Rickettsia typhi) carried by fleas and spread by their feces, not to be confused with typhoid fever that is caused by a different bacteria, Salmonella typhi. This is yet another reason you should not scratch bites or touch gross looking wounds on your body...you never know what you might be further spreading into them. The symptoms of murine typhus include headache, fever, rash, vomiting, chills, and muscle pain. It can be fatal but is nowhere near as deadly as epidemic typhus transmitted by lice. There were 33 cases reported in 2008 from Travis county and cases have been increasing over the last decade.

So murine typhus is a bacterial endomicroparasite living within a macroparasitic flea! Even our parasites get parasites! Now, you're probably more concerned with what this means for humans. During my Nerd Nite talk I warned that this year would be especially good for flea survival because of increased spring time precipitation and thus could increase flea-borne diseases. Fleas need a humid environment for their larvae to survive; this is why it is so important to clear brush that might create a hospitable microclimate. Sadly, a month after that talk a north Travis county resident died from murine typhus. So far there have only been 2 reported cases from Travis county, which is far lower than the previous year's total of 54...but we still have months to go. So now is the time to get the word out.

I made the above graph just to illustrate visually how much the disease is increasing. Last year there was more than a 100%  increase of the disease from the year before and more than 3 times the cases in 2010 within Travis county. This is a new record within Texas and Travis county for cases! 

Now if you've been paying attention you may have found an inconsistency with my logic from the previous paragraph. Earlier I stated that increased precipitation leads to more fleas and thus more flea-borne diseases...but according to this graph, last year during the worst drought in Texas history, murine typhus cases sky rocketed! My hypothesis is that the normal animal hosts of the fleas probably suffered huge population losses forcing fleas to bite pets instead of their normal diet of raccoon, possum, hare, and rodent. Additionally, wildlife is attracted to urban center water sources and if the wildlife are more stressed due to drought, their immune systems may not be fighting off the infection as well leading to higher parasitemias in the blood. While droughts can be good for killing disease vectors, they can also cause them to look for other blood meal sources such as pets and humans. So again, what does this mean? This means that now that we're entering summer after a wet spring...those increased wildlife populations may move into urban centers again looking for water. I would guess we are entering the higher risk months RIGHT NOW.

So what can you do? Here are some tips taken from the Statesman article referenced in the above graph:

■ Keep homes, yards and pets flea-free.
■ Eliminate outdoor pet food that can attract animals with infected ticks or fleas.
■ Avoid places that may be infested with ticks or fleas.
■ Wear long sleeves, slacks, socks and shoes and use insect repellent containing DEET.
Report typhus cases to the health department at 972-5555.
Contact Mary Ann Roser
at 445-3619

Personally, I've found fleas to be bad both this year and last year. Also, ticks can transmit another closely related rickettsial species causing sylvatic typhus so avoid ticks too! Ticks spread a lot of nasty and poorly understood parasites.



Author
Stavana Strutz is a doctoral candidate in the Parmesan lab who studies disease ecology and evolution.