CDC — Parasites

Blood

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Some parasites can be bloodborne. This means:

  1. the parasite can be found in the bloodstream of infected people; and
  2. the parasite might be spread to other people through exposure to an infected person’s blood (for example, by blood transfusion or by sharing needles or syringes contaminated with blood).

Examples of parasitic diseases that can be bloodborne include African trypanosomiasis, babesiosis, Chagas disease, leishmaniasis, malaria, and toxoplasmosis. In nature, many bloodborne parasites are spread by insects (vectors), so they are also referred to as vector-borne diseases. Toxoplasma gondii is not transmitted by an insect (vector).

In the United States, the risk for vector-borne transmission is very low for these parasites except for some Babesia species.

Microscopic red blood cells.

Blood Transfusions

Many factors affect whether parasites that can be found in the bloodstream might be spread by blood transfusion. Examples of some of the factors include:

  • how much of the parasite’s life cycle is spent in the blood;
  • how many parasites might be found in the blood (in other words, the concentration or level of the parasite);
  • how long the parasite stays in the body, in treated and untreated people; and
  • how the parasite affects people. For example, if infected people feel sick, they might not want to donate blood or they might be deferred (turned away).

Some parasites spend most or all of their life cycle in the bloodstream, such as Babesia and Plasmodium species. Parasites, such as Trypanosoma cruzi, might be found in the blood early in an infection (the acute phase) and then at much lower levels later (the chronic phase of infection). Other parasites only migrate (travel) through the blood to get to another part of the body.

There may be cases of transfusion-transmitted parasites that go undetected and unreported, but the risk for infection is very low compared with the number of blood transfusions. In the United States since 1980, there have been published reports of cases of transfusion-associated babesiosis (>150), malaria (

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50), and Chagas disease (

5). Since 1965, there have been published reports of transfusion-associated toxoplasmosis (

Blood Donor Screening

Potential blood donors are asked if they have had babesiosis or Chagas disease. If the answer is «yes,» the person is deferred from donating blood.

Potential blood donors are also asked about their recent international travel. People who traveled to an are where malaria transmission occurs are deferred from donating blood for 1 year after their return to the United States. Former residents of areas where malaria transmission occurs will be deferred for 3 years. People diagnosed with malaria cannot donate blood for 3 years after treatment, during which time they must have remained free of symptoms of malaria.

Donated blood is tested for a number of infectious agents. Currently, most of the U.S. blood supply is screened for Trypanosoma cruzi (the parasite that causes Chagas disease). If the results are positive, the blood center will try to notify the donor. People who test positive should consult a health care provider. Health care providers may contact CDC for confirmatory testing and management information, including treatment.

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Parasites of Madagascar’s Lemurs Expanding With Climate Change

Study could help identify potential disease hotspots before they become a problem

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Rising temperatures and shifting rainfall patterns in Madagascar could fuel the spread of lemur parasites and the diseases they carry.

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By combining data on six parasite species from ongoing surveys of lemur health with weather data and other environmental information for Madagascar as a whole, a team of Duke University researchers has created probability maps of likely parasite distributions throughout the island today.

Then, using climate projections for the year 2080, they estimate what parasite distributions might look like in the future.

«We can use these models to figure out where the risk of lemur-human disease transmission might be highest, and use that to better protect the future of lemur and human health,» said lead author Meredith Barrett, who conducted the study while working as a graduate student at Duke.

Lemurs are native to the African island of Madagascar, where climate change isn’t the only threat to their survival. More than 90 percent of the lemurs’ forest habitat has already been cleared for logging, farming and grazing. Illegal hunting for bushmeat is also a problem.

A key part of saving these animals is ensuring that they stay healthy as environmental conditions in their island home continue to shift, Barrett said.

Average annual temperatures in Madagascar are predicted to rise by 1.1 to 2.6 degrees Celsius by 2080. Rainfall, drought and cyclone patterns are changing too.

In a study published in the January 2013 issue of the journal Biological Conservation, Barrett and colleagues examined what these changes could mean for lemur health by taking a cue from the parasites they carry.

The team focused on six species of mites, ticks and intestinal worms commonly known to infect lemurs. The parasites are identified in lemur fur and feces. Some species — such as pinworms, whipworms and tapeworms — cause diarrhea, dehydration and weight loss in human hosts. Others, particularly mites and ticks, can transmit diseases such as plague, typhus or scabies.

When the researchers compared their present-day maps with parasite distributions predicted for the future, they found that lemur parasites could expand their range by as much as 60 percent. Whipworms, for example, which are now largely confined to Madagascar’s northeast and western coasts, may become widely distributed on the country’s southeastern coast as well.

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Anne Yoder, senior author on the study and Director of the Duke Lemur Center, said the research is particularly important now as lemurs have been identified by the International Union for the Conservation of Nature (IUCN) as the most endangered mammals on earth.

Warmer weather means that parasites could grow and reproduce more quickly, or spread to higher latitudes and elevations where once they were unable to survive. As lemur parasites become more prevalent, the diseases they carry could show up in new places. The spread could be harmful to lemur populations that have never encountered these pests before, and lack resistance to the diseases they carry.

Shifting parasite distributions could have ripple effects on people too. As human population growth in Madagascar drives people and their livestock into previously uninhabited areas, wildlife-human disease transmission becomes increasingly likely.

The authors hope their results will help researchers predict where disease hotspots are likely to occur, and prepare for them before they hit.

Meredith Barrett is now a postdoctoral scholar with the Robert Wood Johnson Foundation Health & Society Scholars Program at the University of California at San Francisco and Berkeley. Jason Brown of Duke University and Randall Junge of the Columbus Zoo & Aquarium were also authors of this study.

Funding was provided by the National Science Foundation, the Saint Louis Zoo Field Conservation for Research Fund, Duke University Center for International Studies, Duke University Graduate School, Nicholas School of the Environment and the Robert Wood Johnson Foundation.

today.duke.edu

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