Tuesday, February 10, 2015

Spittin' ELISAs: Using Saliva to Detect Parasitic Infections

Over the weekend I attended a League of Legends tournament with my wonderful husband. Despite anticipating losing a day's worth of work, I wound up hanging out with another fellow parasitophile and then I got an e-mail from my advisor with a paper that I hadn't read yet. So, there I was, reading about detecting Trypanosoma cruzi via ELISA from salivary samples of modern people (well, people from 1995 anyway...). The paper's intro cited one study I was familiar with and FIVE that I wasn't. From that point on, I knew I'd be (eagerly and enthusiastically) reading a lot more over the weekend.

So this is a post for me for you. This is me reminding myself of what I learned and sharing it with you, which I suppose has been the goal of this blog all along.  I guess it just seems more overt at the moment.

Before we jump too far ahead, let's start by talking about what ELISAs are. ELISA stands for "enzyme-linked immunosorbent assay". It's a fancy phrase, but don't let it scare you too much; the concept is fairly straightforward. Essentially, when you are infected with a parasite, the parasite produces antigens that are specific to whichever parasite is infecting you. In response, your body produces antibodies that are specifically designed to deal with the infection of that parasite. ELISAs are tests that are designed to detect either the parasite antigen or the antibody produced in response to said antigen.

Each ELISA kit is parasite-specific to some degree or another. This is really dependent on the parasite. Some kits can detect antigens/antibodies produced by/in response to a particular species, while others can only detect parasites at the genus level, so you may not know exactly which parasite you have. In the medical world, this is sort of "good enough for government work" as you can often treat infections with species belonging to the same genus in the same manner effectively. (If you have a parasite that is susceptible to a the same treatment protocols as a different parasite, it doesn't really matter what you are treating for as long as the treatment works.) As parasite ELISAs are most often used in medical and veterinary settings for rapid diagnosis, the specificity is less of an issue. However, in the case of parasitological research, we have to be careful when we use ELISAs to assess parasitism. We have to pick the kits carefully and be aware of potential cross-reactivatity.

Parasite ELISAs typically work with two types of material: blood and feces. (Wooo-hoo!) As you might imagine, intestinal parasites are typically detected from feces while non-intestinal types of parasites are found via blood serum. The problem with serum is that acquiring it is invasive (and for those of us that study archaeoparasitology, not available for use). Interestingly, your body carries antigens and produces antibodies that wind up in places other than serum...say for example, in your saliva. Really brilliant people in the late 1980s and early 1990s figured out that you could detect a number of pathogens via ELISA testing using patient saliva rather than serum. The Chagas' paper I mentioned earlier cited three studies that found viral infections, two that demonstrated parasitic infections, and one that detected bacterial infections. The two parasitic infections were chronic schistosomiasis (Garcia and colleagues, 1995) and acute toxoplasmosis (Hajeer and colleagues, 1994). Plus the paper on Chagas', of course.

It seems that that literature grows silent on this topic after the 1990s. It doesn't seem that people found evidence that these previous studies were incorrect (as far as I can tell), so I'm wondering if it just fell off of people's radar or if it just became so well-accepted that people stopped writing about it. It's hard to say one way or the other from my limited knowledge of the parasite ELISA literature, but I'm excited to have found something that leads to more. (Before Saturday, only knew about the Hajeer paper, so now I have a little bit more to build off of, which is super exciting for me!)

The Moral of the Story
The point of all this is to tell those of you who, like me, knew/know very little about molecular work and its application to the field of parasitology. Testing saliva from people and animals is a quick, non-invasive way to do preliminary tests for certain types of parasites. It's amazing how far our technology has advanced and it will be interesting to see how these advancements help us to better understand parasitism in the world around us, past, present, and future. I'm hoping to find more parasite studies looking at the application of ELISA testing that utilizes saliva as the detection source, so this is also a request to keep your eyes and ears open and let me know if you know of work being done in the area. (Thanks in advance to those of you that actually do!)