this junction, the uterus opens into the genital atrium; this opening is surrounded by Mehlis glands. In some flukes, the terminal end of the uterus is strengthened with muscles and spines. F. hepatica reproduces both sexually, via the hermaphrodite adult flukes, and asexually. The miracidia can reproduce asexually within the intermediate snail host. Genome With its draft genome sequence published in 2015, F. hepatica is known to have the largest nuclear genome size among trematodes so far sequenced. It is about 1.3 Gb, which is two times that of Opisthorchis viverrini with 634.5 Mb, the second largest genome among trematodes. The genome is contained in 10 pairs of chromosomes. The protein-coding sequence covers about 21.8 Mb and repetitive DNA sequence about 32% of the total genome. The number of genes predicted is 14,642. The mitochondrial genome consists of 14462 bp, containing 12 protein-encoding, 2 ribosomal and 22 transfer RNA genes. Prevalence Currently, F. hepatica has one of the widest geographical spread of any parasitic and vector-borne disease. Originating in Europe, it has expanded to colonize over 50 countries, covering all continents except Antarctica. In contrast, F. gigantica is generally considered more geographically restricted to the tropical regions of Africa, Asia, and the Middle East, with some overlap between the two species. Climate affects both F. hepatica and its intermediate host, the snail. For example, the development of F. hepatica miracidia and larvae, and the reproduction of Galba truncatula, require a temperature range of 10 to 25 °C. In addition, they both require high levels of moisture in the air, as both are at risk of desiccation. Due to this, the prevalence, along with the intensity of infection, of F. hepatica is primarily dependent on rainfall levels and temperature. Parasitic adaptations F. hepatica's tegument protects it from the enzymes of the host's digestive system, whilst still allowing water to pass through. Free-swimming larvae have cilia and the cercariae have a muscular tail to help them swim through the aquatic environment and also allow them to reach the plants on which they form a cyst. To attach within the host, F. hepatica has oral suckers and body spines. Their pharynges also help them to suck onto the tissues within the body, particularly within the bile ducts. The adult fluke's respiration is anaerobic; this is ideal, as no oxygen is available in the liver. F. hepatica is adapted to produce a large number