The incredible amount of genetic diversity in parasites means humans are often infected with multiple strains, which could make infections worse and increase the prevalence of the parasite over time, according to a new study.
Schistosoma mansoni is a water-borne parasite with two hosts: snails and humans. When eggs in excrement from infected humans make their way into bodies of water, they hatch and infect snails, where they multiply. The parasite leaves the snail and enters the water, where it can infect humans by penetrating the skin.
To figure out what factors influence the amount of damage, or virulence, done to either host, Purdue University researchers studied the effects of two strains separately and then together.
"The amount of virulence that occurs when these two strains are together differs depending on which host they're in," explained Dennis Minchella, a professor of biological sciences at Purdue. "In the snail, the nastier strain was suppressed by the dominant competitor, and the overall virulence was lower. But in the mouse, the harsher strain dominates."
Mice with two strains of the parasite, or unrelated infections, fared similarly to those with only the nastier strain, but much worse than those with the weaker strain. The findings were published in the International Journal for Parasitology.
That the vertebrate still fares as bad or worse when two strains of the parasite are present could be bad news for people in Africa, the Middle East and the tropics, where schistosomiasis affects more than 200 million people. The disease is treatable with drugs, but people who live in areas where the parasite is endemic will likely keep getting sick.
Schistosoma mansoni starts to cause problems for humans several weeks after infection, when worms begin to reproduce. Most eggs exit the body, but some get stuck in the liver and intestines, where they cause inflammation. This leads to swelling and an inflated, enlarged abdomen.
To measure virulence, the researchers divided the weight of the liver by the mouse's total body weight. As the liver becomes enlarged due to parasite eggs, more damage is done to the host, and the ratio of liver to total body weight increases.
Kin Selection Theory, which says that virulence will be higher in a host if multiple strains are competing, aligns with these results. But it may be strain characteristics, rather than genetic relatedness, that are the main drivers of the outcomes in unrelated infections.
Of the two strains used in this study, PR and NMRI, NMRI was clearly the stronger competitor. In mice, the unrelated infection was more virulent than PR only infections, but not significantly different from NMRI only infections. Essentially, the tougher strain went on with business as usual, even when joined by another strain of the parasite.
An increase in genetic diversity and the frequency of unrelated parasitic infections could create more harmful infections for humans, while also increasing the longevity of infections in snail hosts. Together, this could increase the overall prevalence of the parasite over time.
"Understanding how hosts and parasites interact is important when it comes to treating and preventing the disease," Minchella said. "These findings might also be relevant in other parasite systems with two hosts."
Source: Purdue University
Dear Helpdesk: Working in a Toxic Health Care Environment
March 28th 2024Dear Helpdesk is your steadfast companion, offering life coaching and workplace advice from 2 seasoned IPs for some of your most challenging real-life situations. Let us help you navigate the intersection between work and life, guiding you to navigate the dynamic world of infection prevention with confidence and grace. This article is on handling a toxic health care environment.
Product Locator: Spring and Early Mother's Day Gift Guide for Infection Prevention Personnel
March 27th 2024Whether it's a spring holiday, birthdays, or no reason at all, infection prevention personnel love to give and receive gifts that help at the end of a stressful day. Infection Control Today® offers some gift ideas for infection prevention personnel and their families.
Catching Up With Vangie Dennis, AORN 2022-2023 President at AORN 2024
March 26th 2024Infection Control Today (ICT) had the privilege of catching up with Vangie Dennis, MSN, RN, CNOR, CMLSO, at the Association of periOperative Registered Nurses' (AORN’s) International Surgical Conference & Expo 2024. As the former president of AORN and an esteemed figure in perioperative services, Vangie Dennis shared insights into her recent endeavors and the exciting new chapter she's embarked upon.
How To Optimize Your Time Management Strategies for the Busy Infection Preventionist
March 25th 2024Is your calendar resembling a chaotic masterpiece of overlapping tasks? Join the club of infection preventionists striving to balance responsibilities. Dive into proven strategies from a fellow infection preventionist to reclaim control of your time, streamline tasks, and boost productivity effectively. This is an IP Lifeline article.