Kimelea kinaishi katika mwili.

This is because Swahili uses noun classes, and words in the sentence often have to agree with the noun’s class.

Kimelea belongs to the ki-/vi- class in the singular/plural pattern:

• singular: kimelea
• plural: vimelea

Because the subject is kimelea, the verb takes the matching subject prefix ki-:

• ki- = it (for this noun class)
• -na- = present tense
• -ishi = live

So kinaishi literally breaks down as:

• ki-
  • -na-
    • -ishi
• it
  • present
    • live

That agreement is a very important feature of Swahili grammar.

Kinaishi is the verb form, and it can be broken into parts:

• ki- = subject marker for the noun class of kimelea
• -na- = present tense marker
• -ishi = verb root meaning live

So kinaishi means it lives or it is living, depending on context.

In many simple sentences, the Swahili present tense can cover both English ideas:

• it lives
• it is living

Swahili normally does not use articles like the or a/an.

So kimelea can mean:

• a parasite
• the parasite

The exact meaning depends on context.

This is very normal in Swahili. You usually do not need to add anything to show the or a.

Katika means in, inside, or within, depending on context.

Here it introduces the location:

• katika mwili = in the body

It is a common and slightly formal or neutral way to say in.

In everyday speech, Swahili speakers may also use other location forms, depending on the situation.

Yes. A very natural alternative is:

• Kimelea kinaishi mwilini.

Here, mwilini means in the body or inside the body. The ending -ni often marks location.

So these are both possible:

• kimelea kinaishi katika mwili
• kimelea kinaishi mwilini

The version with katika mwili is perfectly correct and clear.
The version with mwilini may sound a bit more compact and very natural as well.

The noun is mwili, meaning body.

The m- is part of the noun itself, not a separate word. In Swahili, many nouns belong to classes with characteristic beginnings. Mwili is a singular noun in the m-/mi- class:

• singular: mwili = body
• plural: miili = bodies

So you should learn mwili as the full word.

The word order here is very straightforward:

• Kimelea = subject
• kinaishi = verb
• katika mwili = location phrase

So the pattern is:

Subject + Verb + Location

That is a very common and natural word order in Swahili.

To make kimelea plural, change it to vimelea. Then the verb must also change to agree with the new noun class:

• singular: Kimelea kinaishi katika mwili.
• plural: Vimelea vinaishi katika mwili.

Changes:

• kimelea → vimelea
• kinaishi → vinaishi

If you wanted to say in the bodies, you could also change the location:

• Vimelea vinaishi katika miili.
• or Vimelea vinaishi miilini.

It can often mean both.

The Swahili -na- present tense is broader than English. Depending on context, kinaishi may be understood as:

• it lives
• it is living

English makes a stronger distinction between simple present and present progressive than Swahili often does.

So in a sentence like this, context tells you whether the meaning is general, habitual, or currently true.

A simple pronunciation guide is:

• ki-me-LE-a
• ki-na-I-shi
• ka-TI-ka
• mWI-li

A few helpful points:

• Swahili vowels are usually pronounced clearly and separately.
• ei or ea-type sequences are usually not reduced the way they often are in English.
• mw in mwili is pronounced together, roughly like mwee-li but with a short, clear vowel.

Swahili pronunciation is generally quite regular once you learn the sound of each letter.

Sometimes yes, but not always with exactly the same feel.

Katika is a solid, standard choice for in/inside/within.
Kwenye is also common in many contexts and is often used for location, roughly like on, at, or in, depending on context.

For this sentence, katika mwili is especially clear for inside the body.
A learner should treat katika mwili as a very safe and correct expression here.

In Swahili, the verb does change, but it changes by adding a subject marker at the beginning rather than changing the ending the way English often does.

Compare:

• ninaishi = I live / I am living
• unaishi = you live
• anaishi = he/she lives
• kinaishi = it lives, for a ki- class noun like kimelea

So the verb does show the subject, but in a different way from English.