can it be caused by the deficiency of any vitamin?
Vitamin B deficiency.
Macrocytic anemia
 An increased red cell distribution width (anisocytosis) also suggests megaloblastosis and is commonly seen in Vitamin B deficiency and folic acid deficiency. 
what is apororhynchus? It a genus of small parasitic spiny-headed  worms. does it cause any disease? Yes, specially in birds. can you name any? Enteritis and anemia. where did it get the name from? The name  was chosen based on the characteristic absence of a proboscis in this species of Acanthocephala. what symptoms does the second disease show? Weakness or fatigue,  poor concentration, shortness of breath on exertion ,increase in  cardiac output.  palpitations, angina , intermittent claudication of the legs, and symptoms of heart failure. how can it be diagnosed? It is typically diagnosed on a complete blood count. what are the different forms of it? Macrocytic anemia, microcytic anemia , and sickle cell anemia. how is the first one different from others? Unlike other types, in this the red blood cells (erythrocytes) are larger than their normal volume.
wiki:2261803
Macrocytic anemia [SEP] Megaloblastic anemias
This type of anemia is caused by impaired DNA synthesis and repair, often from deficient thymidine production. Thiamine responsive megaloblastic anemia syndrome also causes megaloblastic anemia. The red blood cells grow larger because they cannot produce DNA quickly enough to divide at the right time as they grow and thus grow too large before division. Additional causes of megaloblastic anemia include medications that interfere with DNA synthesis or with the absorption or metabolism of Vitamin B12 or folate such as methotrexate, sulfasalazine, metformin, anticonvulsant medications (e.g., valproic acid or phenytoin), certain antibiotics (e.g., trimethoprim/sulfamethoxazole), antiretroviral medications, cholestyramine, triamterene, and nitrous oxide.