What are the evil diseases of Egypt?

In the beginning of Ekev, in Devarim 7:15:

טו וְהֵסִיר ה' מִמְּךָ, כָּל-חֹלִי; וְכָל-מַדְוֵי מִצְרַיִם הָרָעִים אֲשֶׁר יָדַעְתָּ, לֹא יְשִׂימָם בָּךְ, וּנְתָנָם, בְּכָל-שֹׂנְאֶיךָ.

15 And the LORD will take away from thee all sickness; and He will put none of the evil diseases of Egypt, which thou knowest, upon thee, but will lay them upon all them that hate thee.

What are these known diseases? We might leap to think of diseases which manifested during the ten plagues, and perhaps this is correct. But Shadal has an interesting idea, that there are particular diseases which are (or were) specific to Egypt. And he cites Pliny for this. Thus, Shadal writes:

Thus, while he calls in tzaraas, he also gives some Latin: Aegyptus talium vitiorum genitrix.

So I looked up book 26, chapter 5, in Plinius' Historia naturalis, and this is what it said, regarding Elephantiasis, which Pliny treated the same as leprosy :

CHAP. 5--ELEPHANTIASIS.

We have already¹ stated that elephantiasis² was unknown [p. 5155] in Italy before the time of Pompeius Magnus. This malady, too, like those already mentioned, mostly makes its first appearance in the face. In its primary form it bears a considerable resemblance to a small lentil upon the nose; the skin gradually dries up all over the body, is marked with spots of various colours, and presents an unequal surface, being thick in one place, thin in another, indurated every here and there, and covered with a sort of rough scab. At a later period, the skin assumes a black hue, and compresses the flesh upon the bones, the fingers and toes becoming swollen.

This disease was originally peculiar to Egypt. Whenever it attacked the kings of that country, it was attended with peculiarly fatal effects to the people, it being the practice to temper their sitting-baths with human blood, for the treatment of the disease.

So the point here is that it was originally peculiar to Egypt, and this is what the pasuk intends with the diseases of Egypt.

Though Shadal does not make the connection, what Pliny says about treating this tzaraas by tempering sitting-baths with human blood struck a chord. Recall what Rashi says on a pasuk in parshas Shemos, in Shemos 2:23:

23. Now it came to pass in those many days that the king of Egypt died, and the children of Israel sighed from the labor, and they cried out, and their cry ascended to God from the labor.		כג. וַיְהִי בַיָּמִים הָרַבִּים הָהֵם וַיָּמָת מֶלֶךְ מִצְרַיִם וַיֵּאָנְחוּ בְנֵי יִשְׂרָאֵל מִן הָעֲבֹדָה וַיִּזְעָקוּ וַתַּעַל שַׁוְעָתָם אֶל הָאֱ־לֹהִים מִן הָעֲבֹדָה:
Now it came to pass in those many days: that Moses sojourned in Midian, that the king of Egypt died, and Israel required a salvation, and Moses was pasturing, and a salvation came through him. Therefore, these sections were juxtaposed [i.e., the section dealing with the king of Egypt’s affliction, and that dealing with Moses pasturing flocks]. [From an old Rashi]		ויהי בימים הרבים ההם: שהיה משה גר במדין, וימת מלך מצרים והוצרכו ישראל לתשועה. ומשה היה רועה וגו' (ג א) ובאת תשועה על ידו, ולכך נסמכו פרשיות הללו:
that the king of Egypt died: He was stricken (נִצְטָרַע), and he would slaughter Israelite infants and bathe in their blood. [From Exod. Rabbah 1:34]		וימת מלך מצרים: נצטרע והיה שוחט תינוקות ישראל ורוחץ בדמם:

Note that this is taken from Shemot Rabba, or else Shemot Rabba takes from it. Shemot Rabba was composed about the time of Rashi. And perhaps this is an old tradition of what evil Pharaoh did, or perhaps, aware of Pliny's words on the subject of the treatment of tzaraas, the midrashist composed this midrash, to account for the crying out of the Israelites in proximity to the king of Egypt's "death"; and combined with a method of keeping the same king even though he "died", by making him a leper; or to parallel an earlier Pharaoh who was stricken with leprosy on account of Sarah.

While we are discussing Shadal, here is a note he makes on the next pasuk:

טז וְאָכַלְתָּ אֶת-כָּל-הָעַמִּים, אֲשֶׁר ה' אֱלֹהֶיךָ נֹתֵן לָךְ--לֹא-תָחוֹס עֵינְךָ, עֲלֵיהֶם; וְלֹא תַעֲבֹד אֶת-אֱלֹהֵיהֶם, כִּי-מוֹקֵשׁ הוּא לָךְ. {ס}

16 And thou shalt consume all the peoples that the LORD thy God shall deliver unto thee; thine eye shall not pity them; neither shalt thou serve their gods; for that will be a snare unto thee. {S}

טז ] כי מוקש הוא : כל אחד מהגויים ההם , אם תקיימהו אצלך , יהיה לך למוקש , שתעבוד את אלהיהם ותסור מאחרי ה.

To see in part what he is discussing, in making each nation a snare, rather than the idolatry, and the being ensnared as serving their idols and thus straying from after Hashem -- this is essentially Seforno's parse of the pasuk. See this post at Hirhurim about this pasuk, and my comments in the comment section.