Chagas Disease and Pets

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chagas disease dogs

Kissing Bugs are really not as loving as their nickname suggests. The kiss may cause swelling that will go away but it’s what happens afterwards that poses the biggest problem. These cone nose critters (triatomine) will descend on any mammal and typically bite around the mouth or the eye. The bite itself will not transmit diseases. This next part may gross you out a bit. When the bugs bite, they defecate. The target – generally asleep – will brush away the bug and smear the feces into the bite wound or a mucous membrane (eye or mouth).

Normally, the swipe wouldn’t be a problem since only a little more than 50% of the kissing bugs in the United States are infected vectors for a parasite called Trypanosoma cruzi (T. cruzi), which causes Chagas Disease. In addition, the actual transfer of the parasite via the bug is very inefficient according to the Centers for Disease Control and Prevention (CDC). Think about it, the World Health Organization estimates 7 million people – primarily living in Central and South America – are infected, although the entire population in the southern continent is 626 million.

But still, why are 7 million people infected? Well, you cannot blame all of the parasitic transfers on the kissing bugs. The bugs are simply the occasional so-called taxi drivers. The parasite needs hosts or reservoirs to survive and those are mammals. So, mammals pass it to the bugs who then pass it along.

T. cruzi can also be contracted through infected meat, ingestion of bugs, blood transfusions, organ transplantation, placenta and sex. (Casual contact is still fine.) Screening systems are in place to minimize the transmission risk via blood transfusions. In the United States, the Food and Drug Administration (FDA) approved an assay to test blood from transfusions for Chagas Disease but did not make it mandatory. The American Red Cross and other major blood donation organizations have adopted the test, discard the blood if positive, and try to contact the donor. At Hemopet, we screen for trypanosomes, too, and would disqualify the donor dog, if positive.

Another reason why so many people are still infected is due to the lack of a vaccine and socioeconomics. Kissing bugs live in the roofs of thatched and mud homes, which are occupied by poorer people in rural communities.

Overall, Chagas Disease is rare. With that being said, it is on the rise in the United States. The trend could be due to global warming, the transfer of goods across borders, migration, and the recent study that bed bugs can transmit T. cruzi as well.

In fact, the College of Veterinary Medicine at Texas A & M University tested 205 Texas shelter dogs and discovered that 9% had chronic Chagas Disease. If you think about it, many of these dogs were probably strays and slept in similar conditions to the more vulnerable human communities. The 9% probably does not reflect the number of potential house pets that have had exposure to Chagas. 

Bear in mind, this is not a reason to refuse to adopt a dog with the disease into your loving home or to relinquish your own companion pet, if positively diagnosed with Chagas. For the parasite to move from the dog to a person, it needs to go through the kissing bug. The dog can only pass the parasite to the bug at the beginning of the infection.

Disease Progression

Several commonalities exist between human and dog manifestations of the disease. The disease has two phases: acute and chronic. In the acute phase, the level of parasitemia is high and often detected in the blood under a microscope. The parasitemia decreases even without treatment and is undetectable by microscope in the chronic phase. So, diagnosis of chronic Chagas Disease relies on blood antibody tests.

Acute symptoms are usually mild in dogs and include fever, depression, lethargy, diarrhea, lack of appetite, swollen lymph nodes or enlarged liver or spleen. These symptoms will not be present until around 5 to 40 days after infection, which may hinder diagnosis, plus they generally resolve on their own. Rarely, but sometimes, cardiac dysfunction can occur during the acute phase and acute myocarditis may cause arrhythmias or sudden collapse and death.

The chronic phase is fascinating. Human studies have shown that approximately 70-80% of humans infected with the T. cruzi parasite have indeterminate forms of Chagas Disease which means they show no symptoms or physical abnormalities even upon death. They will remain infected for life if unsuccessfully treated and can still pass along the disease, but not as much as someone in the acute phase.

The other 20-30% of humans usually develop some form of heart disease.

Typically though, people living in the Southern Cone of South America may develop gastrointestinal tract disease instead. Although canine studies have not been conducted at this level, it appears that the canine population’s ratios of indeterminate vs. symptomatic cases mirror humans. Eventually, dogs that do present symptoms of heart disease develop chronic myocarditis, usually with cardiac dilatation and arrhythmias. The degree of complications in both species likely relates to age, activity level, and most importantly the genetic mutation of the parasite. Additionally, T. cruzi infection in patients who become immunocompromised may reactivate, leading to increases in intracellular parasite replication.

Treatment

The anti-parasitic drugs, nifurtimox and benznidazole, combat the infection. The side effects can be severe and can include devastating consequences on the liver and renal systems. To give you an idea of the danger of these drugs: the FDA has not approved the medications for prescription use; only the CDC can dispense the medication. I highly doubt that the CDC would allow the drugs to be given to dogs. Dogs that develop chronic heart conditions due to Chagas Disease can be placed on the appropriate heart medication.

I have heard about experiemental treatments that are occurring around the United States. Once more information is available about the success rate of these treatments, I will update this article or write a follow-up.

Prevention/Heartworm

Housing in the United States is fairly well sealed from the environment so I would not worry about the bugs invading the home. But, you can reduce the risk in the yard and around your home.

  • Sealing cracks and gaps around windows, walls, roofs, and doors
  • Removing wood, brush, and rock piles near your house
  • Using screens on doors and windows and repairing any holes or tears
  • If possible, making sure yard lights are not close to your house (lights can attract the bugs)
  • Sealing holes and cracks leading to the attic, crawl spaces below the house, and to the outside
  • Keeping pets indoors at night and having them sleep indoors
  • Keeping your house and any outdoor pet resting areas clean, in addition to periodically checking both areas for the presence of bugs

I believe the use of insecticides against the triatomine bugs is pointless at this time as the threat of the T. cruzi transmission is low and no chemicals have been approved for use against the kissing bugs. Additionally, roach hotels or other “bait” formulations do not work against triatomine bugs.

Even though heartworm preventatives are antiparasitic drugs, they have not been proven to work against the T. cruzi parasite. I highly doubt that heartworm preventatives ever
will be proven to work against the T. cruzi parasite, as it is a different parasite than heartworms and affects pets’ bodies differently.

Although we don’t know which dogs will develop a determinate chronic Chagas Disease due to the T. cruzi parasite’s mutation, prevention begets common sense to keep your dog’s immune system healthy with the right food choices and giving booster vaccines only as appropriate or required by law.

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843

References

“American Trypanosomiasis.” Centers for Disease Control and Prevention, n.d. Web. 28 Feb. 2016. http://www.cdc.gov/dpdx/trypanosomiasisAmerican/index.html.

“American Trypanosomiasis (Chagas Disease).” Encyclopedia of Parasitology (n.d.): n. pag. The Center for Food Security & Public Health. Iowa State University College of Veterinary Medicine, Sept. 2009. Web. 28 Feb. 2016. http://www.cfsph.iastate.edu/Factsheets/pdfs/trypanosomiasis_american.pdf.

Bern, Caryn, MD, et al. “Evaluation and Treatment of Chagas Disease in the United States.” Journal of American Medical Association. JAMA Network, 14 Nov. 2007. Web. 28 Feb. 2016. http://jama.jamanetwork.com/article.aspx?articleid=209410.

“Chagas Disease (American Trypanosomiasis).” World Health Organization. N.p., Mar. 2015. Web. 28 Feb. 2016. http://www.who.int/mediacentre/factsheets/fs340/en/.

Doucleff, Michaeleen. “Dogs Carry Kissing Bug Disease In Texas And Latin America.” NPR, 16 July 2014. Web. 28 Feb. 2016. http://www.npr.org/sections/goatsandsoda/2014/07/16/331729614/dogs-spread-kissing-bug-disease-in-texas-and-latin-america.

Frazer, Jennifer. “Bed Bugs, Kissing Bugs Linked to Deadly Chagas Disease in U.S.” Scientific American, 10 Dec. 2014. Web. 28 Feb. 2016. http://www.scientificamerican.com/article/bed-bugs-kissing-bugs-linked-to-deadly-chagas-disease-in-u-s/.

“Kissing Bugs and Chagas Disease in the U.S.” Texas A&M University, n.d. Web. 28 Feb. 2016. http://kissingbug.tamu.edu.

“Parasites – American Trypanosomiasis (also Known as Chagas Disease).” Centers for Disease Control and Prevention, 05 July 2012. Web. 28 Feb. 2016. http://www.cdc.gov/parasites/chagas/gen_info/index.html.

Yong, Ed. “Genes from Chagas Parasite Can Transfer to Humans and Be Passed on to Children.” National Geographic, 14 Feb. 2010. Web. 28 Feb. 2016. http://phenomena.nationalgeographic.com/2010/02/14/genes-from-chagas-parasite-can-transfer-to-humans-and-be-passed-on-to-children.

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