Small, fast, and crowded: Mammal traits amplify tick-borne illness

Chipmunks are small-bodied animals with fast lives and dense populations. When ticks feed on them, they are more likely to pick up multiple disease-causing pathogens. Credit: © dwags / Fotolia

In the U.S., some 300,000 people are diagnosed with Lyme disease annually. Thousands also suffer from babesiosis and anaplasmosis, tick-borne ailments that can occur alone or as co-infections with Lyme disease. According to a new paper published in PLOS ONE, when small, fast-living mammals abound, so too does our risk of getting sick.

In eastern and central North America, blacklegged ticks are the primary vectors for Lyme disease, babesiosis, and anaplasmosis. The pathogens that cause these illnesses are widespread in nature; ticks acquire them when they feed on infected animals.

Richard S. Ostfeld, the paper's lead author and a scientist at the Cary Institute of Ecosystem Studies, has researched the ecology of Lyme disease since 1992. "A pattern emerged in our long-term studies. Ticks that fed on certain rodents and shrews were much more likely to pick up multiple pathogens, making the environment riskier for people."

To investigate why mammals differ in their 'reservoir competence' or ability to transmit pathogens to ticks, Ostfeld and his co-authors from Bard College, Oregon State University, the University of South Florida, and EcoHealth Alliance took a two-pronged approach.

First, they looked at life history traits for nine mammals known to harbor Lyme disease, babesiosis, and anaplasmosis. Attributes like body size, litter size, and life span were taken into consideration.

Then they looked at the role of mammal population density. As 'sit and wait' parasites, ticks are much more likely to encounter animals with dense populations. This, in turn, could help pathogens evolve to exploit specific hosts, resulting in more effective transmission rates.

For Lyme disease and anaplasmosis, fast life history features were a strong predictor of an animal's ability to transmit infection to ticks. Body size was inversely related to reservoir competence. Raccoon, skunk, opossum, squirrel, and deer infected fewer ticks than their mouse, chipmunk, and shrew counterparts.

Ostfeld notes, "This is consistent with past research on Lyme disease, West Nile virus, and Eastern Equine encephalitis. There is evidence that animals that mature early and have frequent, large litters invest less in some immune defenses, making them better pathogen hosts."

Population density was the best predictor of species' abilities to transmit all three pathogen groups, with animals that ticks encountered most frequently being the most effective at transferring infection. Co-author Felicia Keesing of Bard College explains, "Fast life history and high population density often go hand-in-hand. In rodents and shrews, pathogen adaptation and poor immune defense may be working together to amplify disease spread."

With Ostfeld concluding, "In our struggle to manage the ever-growing list of tick-borne diseases, we need to understand which animals magnify human disease risk. Our results suggest when generalist pathogens emerge, small mammals with large populations and a fast pace of life warrant careful monitoring."

Source: Cary Institute of Ecosystem Studies

The bloody truth: How blood donations can save animals' lives

Donated blood can be quickly regenerated by the animal’s organism. Credit: Felizitas Steindl / Vetmeduni Vienna

Blood transfusions are of importance not only in human medicine. Also animals do need blood donations. The University of Veterinary Medicine, Vienna operates a blood bank for dogs for more than a decade. But also cats can donate blood for acute emergencies. Horses need blood donations especially during operations that involve high blood loss. Sheep, goats and other ruminants require transfusions when plagued by serious infestations of parasites. Three vets from different areas of expertise explain how blood transfusions work with different animal species and how they can save lives.

Blood can hardly be created through artificial means, but it can be transferred within a species. Reasons for a blood transfusion among dogs and cats are usually serious accidents, large operations, certain types of cancer, cases of intoxication with rat poison, serious infectious diseases such as the tick-borne babesiosis, and blood illnesses including haemolytic or inherited bleeding disorders such as haemophilia.

At the University of Veterinary Medicine, Vienna dog owners can bring their animals to donate blood regularly or as needed. Blood donations two to four times a year per dog is the maximum. About 15 minutes are required for a donation. Dogs must have a minimum weight of 25 kilograms and usually donate about 450 millilitres of blood. For cats, depending on their size, the amount taken is about 50 millilitres. Cats are typically sedated for the procedure. For most dogs, on the other hand, donating blood does not involve any serious stress. Should a donation cause too much anxiety or stress, the animal will be excluded as a donor.

Not all blood is alike

As with people, animals also have different blood types. Animal blood, as well as human blood, is divided into various groups based on different surface proteins found on the red blood cells. More than twelve different blood type systems have been described for dogs, although in practice dogs are only tested for DEA 1.1 positive or DEA 1.1 negative. Cats exhibit three different types of blood, horses eight and bovines eleven. The transfusion of an unsuitable blood type can have fatal consequences for animals, especially when a cat with blood type B receives type A blood. For horses and ruminants, the first time transfusion of 'wrong' donor blood is generally safe. With each additional transfusion, however, blood types become crucial, as the animals have produced antibodies against the foreign blood that can cause serious immune reactions.

Blood donations come with a health check

Dogs and cats can be registered as blood donors at the Clinical Unit of Internal Medicine Small Animals of the Vetmeduni Vienna. The animals receive a donor card and undergo a thorough examination before each donation. This mandatory health check includes a complete blood count, a test for blood parasites, and a check-up for viral infections.

"Donating blood does not harm the animals. The donated amount can be quickly regenerated by the animal's organism," says specialist for small animal internal medicine and blood bank coordinator Nicole Luckschander-Zeller. "We pay special attention to making sure that donor animals feel good during donation. That's why, after every donation, we give the animals a little snack."

Dog and cat blood is not only used as a whole. Individual blood components, such as plasma or erythrocyte concentrates, are stored and used when needed.

Horses as blood donors and recipients

There are various reasons for blood donations in equine medicine. These include clotting disorders of the blood, anaemia, poisonings or serious infectious diseases as well as perioperative blood loss. For the latter, blood is stored and kept ready for use during surgery in areas with strong blood supply, such as the nose and jaw. A blood transfusion helps to sustain adequate circulation of the animal during the operation and speeds recovery.

"The owners of diseased horses occasionally bring the suitable donor animal with them," says René van den Hoven, director of the Clinical Unit for Equine Internal Medicine at the Vetmeduni Vienna. The hospital also maintains a number of its own donor horses. The number of donations and the volume of the blood collected are registered in the horse's file, making it possible to plan future dates for donations without compromising the animal's health.

A maximum of five to seven litres of blood can be collected from a horse per donation. The blood must then be transfused into a patient within just a few hours. Storing whole equine blood is not a suitable option. As only plasma is desired for some treatments, the plasma is separated from the whole blood. Plasma is used for specific applications, for example to improve the healing of complicated wounds or during eye operations. Patients with massive protein loss can also be successfully treated with plasma. Protein loss may occur as a consequence of serious burn trauma, severe diarrhoea, tumours or chronic inflammatory intestinal disease, pleurisy or peritonitis.

Ruminants with anaemia need donated blood

Sheep, goats, lamas and alpacas are especially at risk of being infested by blood-sucking parasites out on the pasture. Ingested through the mouth, the worms come to inhabit the intestinal tract. A high level of parasitic infestation leads to serious cases of anaemia that may be fatal for the animals. "These acute patients require a rapid blood transfusion. Ruminants also receive blood for wounds with heavy blood loss, though this luckily is not often the case," explains the specialist for ruminant medicine, Lorenz Khol

Source:University of Veterinary Medicine -- Vienna

Nanotechnology against malaria parasites

After maturation, malaria parasites (yellow) are leaving an infected red blood cell and are efficiently blocked by nanomimics (blue). Credit: Fig: modified by University of Basel with permission from ACS

Malaria parasites invade human red blood cells, they then disrupt them and infect others. Researchers at the University of Basel and the Swiss Tropical and Public Health Institute have now developed so-called nanomimics of host cell membranes that trick the parasites. This could lead to novel treatment and vaccination strategies in the fight against malaria and other infectious diseases. Their research results have been published in the scientific journal ACS Nano.

For many infectious diseases no vaccine currently exists. In addition, resistance against currently used drugs is spreading rapidly. To fight these diseases, innovative strategies using new mechanisms of action are needed. The malaria parasite Plasmodium falciparum that is transmitted by the Anopheles mosquito is such an example. Malaria is still responsible for more than 600,000 deaths annually, especially affecting children in Africa (WHO, 2012).
Artificial bubbles with receptors

Malaria parasites normally invade human red blood cells in which they hide and reproduce. They then make the host cell burst and infect new cells. Using nanomimics, this cycle can now be effectively disrupted: The egressing parasites now bind to the nanomimics instead of the red blood cells.

Researchers of groups led by Prof. Wolfgang Meier, Prof. Cornelia Palivan (both at the University of Basel) and Prof. Hans-Peter Beck (Swiss TPH) have successfully designed and tested host cell nanomimics. For this, they developed a simple procedure to produce polymer vesicles -- small artificial bubbles -- with host cell receptors on the surface. The preparation of such polymer vesicles with water-soluble host receptors was done by using a mixture of two different block copolymers. In aqueous solution, the nanomimics spontaneously form by self-assembly.

Blocking parasites efficiently

Usually, the malaria parasites destroy their host cells after 48 hours and then infect new red blood cells. At this stage, they have to bind specific host cell receptors. Nanomimics are now able to bind the egressing parasites, thus blocking the invasion of new cells. The parasites are no longer able to invade host cells, however, they are fully accessible to the immune system.

The researchers examined the interaction of nanomimics with malaria parasites in detail by using fluorescence and electron microscopy. A large number of nanomimics were able to bind to the parasites and the reduction of infection through the nanomimics was 100-fold higher when compared to a soluble form of the host cell receptors. In other words: In order to block all parasites, a 100 times higher concentration of soluble host cell receptors is needed, than when the receptors are presented on the surface of nanomimics.

"Our results could lead to new alternative treatment and vaccines strategies in the future," says Adrian Najer first-author of the study. Since many other pathogens use the same host cell receptor for invasion, the nanomimics might also be used against other infectious diseases. The research project was funded by the Swiss National Science Foundation and the NCCR "Molecular Systems Engineering."

Source: University of Basel