def _process_diseases(self, limit=None):
        """
        This method processes the KEGG disease IDs.

        Triples created:
        <disease_id> is a class
        <disease_id> rdfs:label <disease_name>
        :param limit:
        :return:

        """

        LOG.info("Processing diseases")
        if self.test_mode:
            graph = self.testgraph
        else:
            graph = self.graph
        line_counter = 0
        model = Model(graph)
        raw = '/'.join((self.rawdir, self.files['disease']['file']))
        with open(raw, 'r', encoding="iso-8859-1") as csvfile:
            filereader = csv.reader(csvfile, delimiter='\t', quotechar='\"')
            for row in filereader:
                line_counter += 1
                (disease_id, disease_name) = row

                disease_id = 'KEGG-'+disease_id.strip()
                if disease_id not in self.label_hash:
                    self.label_hash[disease_id] = disease_name

                if self.test_mode and disease_id not in self.test_ids['disease']:
                    continue

                # Add the disease as a class.
                # we don't get all of these from MONDO yet see:
                # https://github.com/monarch-initiative/human-disease-ontology/issues/3
                model.addClassToGraph(disease_id, disease_name)
                # not typing the diseases as DOID:4 yet because
                # I don't want to bulk up the graph unnecessarily

                if not self.test_mode and (
                        limit is not None and line_counter > limit):
                    break

        LOG.info("Done with diseases")
        return
This method processes the KEGG disease IDs.

        Triples created:
        <disease_id> is a class
        <disease_id> rdfs:label <disease_name>
        :param limit:
        :return: