Domesticated dogs, genomes, and malaria

Plasmodium falciparum is a unicelluar protozoan parasite of humans and the deadliest species of Plasmodium. It is transmitted through the bite of a female Anopheles mosquito and responsible for Therefore it is regarded as the deadliest parasite in humans, causing at least one million deaths every year. The species evolved about 10,000 years ago from the malarial parasite found in gorillas. A World Health Organization report in 2015, suggested there were 214 million cases of malaria worldwide.

Dogs spread across the globe with humans and have had to adapt to the same environmental conditions as humans. A Chinese research team led by Zhang has successfully identified genes selected in African dogs and functionally verified the action of one of these as the first evidence of dog adaptation to malaria.

“Recently, we have shown the first evidence that dogs can undergo similar adaptations as humans, using the same genes to live in the high altitudes of Tibet,” said professor Ya-Ping Zhang.

“Dogs have survived in tropical environments for thousands of years alongside humans,” said Zhang. “In this study, we have identified genes associated with insulin secretion and sensitivity, immunity, angiogenesis and ultraviolet protection showed adaptive selection.”

Yan-Hu Liu et al. (2017) sequenced the genomes of 19 dogs from Nigeria. For this new data set, they identified a set of candidate genes for natural selection in African village dogs and also carried out functional studies to confirm that one of these, ADGRE1, might be responsible for providing host immunity to Plasmodium infection—a target of selection associated with malaria.

“Our study suggests ADGRE1 also contributes to defense against Plasmodium infection in dogs, and thus, convergent evolution in this gene between humans and dogs,” said Guo-Dong Wang. “This is a novel finding since in earlier studies the most apparent cases of convergent evolution between humans and dogs were in genes for digestion and metabolism, neurological process, and cancer.”

The authors went on to show in cell culture experiments in the lab that the derived variant of ADGRE1 is linked to increased phagocytosis in cells infected with Plasmodium parasites, making it very likely that the ADGRE1 confers protection against Plasmodium infection by stimulating the immune response against the parasite.

In addition, they investigated the Nigerian dogs’ demographic history in relation to other dogs, including Eurasian gray wolves and African golden wolves. They found that the Nigerian dog population diverged from Eurasian dog populations around 14,000 years ago. After this divergence, the population fell on hard times, and experienced a severe bottleneck (leading to a reduced genetic diversity within the Nigerian dog population) and also gene flow from African golden wolves after the divergence.

Finally, they explored signals of selection in the Nigerian dog samples, and identified a number of candidate genes that are also linked to dietary and environmental factors.

As the authors note, since ADGRE1 has also been implicated in an adaptive response to Plasmodium in humans, it makes for a nice genetic tale of dogs utilizing similar tricks from living alongside their human companions to adapt to new environments.

References

Caspermeyer J. 2017. Scientists Find Evidence Our Best Friends, Dogs, Similarly Adapted to Malaria in Africa, Molecular Biology and Evolution,  msx289, https://doi.org/10.1093/molbev/msx289

Liu Y-H, Wang L, Xu T, Guo X, Li Y, Yin T-T, Yang H-C, Yang H, Adeola AC, Sanke OJ, et al. 2017. Whole-genome sequencing of African dogs provides insights into adaptations against tropical parasites. Molecular Biology and Evolution.

 Advance Access published October 10, 2017, doi: 10.1093/molbev/msx258

Wolf parasites in domestic dogs

Grey wolves, like all wild animals, are hosts to a variety of parasites. The presence of grey wolves in German forests has little influence on the parasite burden of hunting dogs. This reassuring conclusion is the result of a new study at the Berlin-based Leibniz Institute for Zoo and Wildlife Research (IZW). The study examined the feces of 78 hunting dogs over several months in an area without wolves and in one that had been recolonized. The results have been published in the open access scientific journal International Journal for Parasitology: Parasites and Wildlife.

Since the early 1990s grey wolves are expanding their range in central Europe. This recolonization gives rise to many questions about this apex predator and its influence on the environment and the life cycles of its parasites, prey, and potential competitors. Scientists at the Leibniz-IZW have now uncovered that the presence of wolves has little impact on the parasite burden of domestic dogs used for hunting prey of wolves. The scientists compared hunting dogs based in Eastern Germany, where wolves have re-established themselves since early 2000, with hunting dogs in North of Germany, where -- at the time of the study -- there were no resident wolf packs.

Grey wolves in the Bavarian forest.Photo Credit: © gallas / Fotolia

"Hunting dogs, unlike companion dogs, are especially well suited for this comparison as they, just like the wolf, rummage through forests and have access to game meat.," Ines Lesniak, a scientist at Leibniz-IZW, explains. "The study focused on the parasites of the internal organs, so-called endoparasites, which can be identified in the feces of the host." In a previous study, the spectrum of endoparasites present in German grey wolves was described. As previously, the researchers used genetic techniques to determine the presence of parasitic worms and protozoan intestinal parasites belonging to the Sarcocystis genus in hunting dogs. Both the rate of infection and the species richness of worms and Sarcocystis species found in the dogs did not differ between the study areas with and without wolves. The parasite spectrum of hunting dogs and wolves overlapped considerably, indicating that dogs might have replaced the wolf during its absence as an alternate and suitable definite host in the life cycles of some parasites. A single Sarcocystis species (Sarcocystis grueneri), previously identified as a "wolf specialist," was discovered more frequently in hunting dogs in wolf areas than in hunting dogs in areas without wolves. Like many tapeworms, these protozoans have a life cycle in which carnivores, like dogs or wolves, function as definite host and their prey, such as roe deer and red deer, act as intermediate hosts.

"Unlike wild animals, hunting dogs are regularly dewormed, including the individual hunting dogs which participated in our study," Lesniak emphasizes. "However, these medical treatments do not affect protozoan parasites such as Sarcocystis." The scientists suspect that the high infection probability of hunting dogs -- over 60 percent in both study areas -- is caused by the routine feeding of game meat or offal. "It's in the owner's hands," Lesniak says. "Many study participants already act very responsibly by deworming their dogs on a regular basis; in the best cases several times a year." The official recommendation of the European Scientific Council for Companion Animal Parasites (ESCCAP) is that there should be a monthly treatment of risk groups such as hunting dogs. Such a regular treatment prevents parasitic worms from reproduction in the host and subsequent egg development, which thereby improves the health and wellbeing of the hunting dog. "Dog owners can also reduce the parasite burden of their dogs by the careful feeding of meat leftovers. Cooking the meat is a simple precautionary measure that inactivates all parasites -- from protozoans to tapeworm cysts -- as well as other pathogens that might be present in the meat." The Leibniz-IZW considers wolves to play a minor role regarding the excretion and distribution of parasites. "The number of wolves in Germany is extremely low compared to other carnivores such as red foxes or raccoon dogs, which can also serve as hosts for these parasites, and it is also low in comparison to the number of hunting dogs," comments the senior author of the study, Dr. Oliver Krone.

German dog owners can rejoice: None of the parasite species found in hunting dogs are an unreasonable health risk to humans, irrespective of whether the dogs live in an area where wolves are present or not present. The regular treatment with anthelmintics and feeding of cooked leftovers are simple but effective measures to maintain the health of hunting dogs. The Leibniz-IZW study illustrates that concerns regarding pathogens related to the return of wolves are currently unjustified.


Citations
Ines Lesniak, Mathias Franz, Ilja Heckmann, Alex D. Greenwood, Heribert Hofer, Oliver Krone. Surrogate hosts: Hunting dogs and recolonizing grey wolves share their endoparasites. International Journal for Parasitology: Parasites and Wildlife, 2017; 6 (3): 278 DOI: 10.1016/j.ijppaw.2017.09.001

Ines Lesniak, Ilja Heckmann, Emanuel Heitlinger, Claudia A. Szentiks, Carsten Nowak, Verena Harms, Anne Jarausch, Ilka Reinhardt, Gesa Kluth, Heribert Hofer, Oliver Krone. Population expansion and individual age affect endoparasite richness and diversity in a recolonising large carnivore population. Scientific Reports, 2017; 7: 41730 DOI: 10.1038/srep41730