Rats and plague
C.B. Kloss, a naturalist working in the Straits Settlements, published this review in 1911 assessing the zoological foundations of Indian plague research and applying its findings to the rat fauna of the Malay Peninsula. The article’s central thesis is that while Indian plague commissions had correctly identified the epidemiological importance of rats, their taxonomic work was riddled with errors—stemming from overreliance on outdated classifications and confusion between normal variation and distinct species—that would mislead any Malayan sanitary officer attempting to replicate the investigations locally.
Summary
Kloss reviews two major Indian publications: Dr. W. C. Hossack’s illustrated account of Calcutta’s plague rats and Surgeon-Captain R. E. Lloyd’s “The Races of Indian Rats.” Both works, while valuable in their epidemiological observations, are faulted for resting on Oldfield Thomas’s 1881 monograph on the genus Mus without acknowledging the substantial taxonomic revisions that had accumulated over the intervening three decades. Lloyd in particular is criticised for mistaking colour “sports” (abnormal variants) of Mus rattus for distinct species, and for failing to recognise that the non-rattus rats with bicoloured tails and spiny coats are rural animals never found in towns—a basic ecological fact that, had it been grasped, would have prevented much of the confusion in his species determinations (pp. 159–161).
The article then pivots to the practical question of which rat species matter for plague control in the Malay Peninsula. Kloss identifies the principal vectors as Mus decumanus (the ship rat, confined to major ports), Mus griseiventer (the common house rat of the southern Peninsula), Mus concolor (a small, spiny-coated form of Mus rattus found in both town and country), and the bandicoot-rats Gonomys varius and G. varillus (introduced species, probably carried in rice-ships from Burma). He provides detailed morphological keys—pelage texture, tail colouration, skull architecture, molar structure, and a previously unnoted feature of the jaw bone—to enable field identification by sanitary officers who may lack zoological training (pp. 163–166).
A comparative analysis of species proportions drawn from Indian and Burmese plague investigations reveals striking regional differences: in Calcutta, Mus decumanus and Nesokia bengalensis dominated the catch, whereas in Rangoon the rattus group (including M. concolor) formed 72 per cent of specimens, with M. decumanus reduced to just 7 per cent. This suggests that the Malayan situation, closer to the Burmese pattern, would present a different epidemiological profile from that of India (pp. 161–162).
Key Findings
- In Calcutta’s northern native quarter, Nesokia bengalensis and Mus decumanus were caught in ratios of 60 and 26 per cent respectively; in the central European quarter these were reversed to 37 and 51 per cent, while Mus rattus formed only 15 per cent of the total (p. 159).
- In Rangoon, Mus rattus plus Mus concolor constituted 72 per cent of plague-related rat specimens, Gonomys species 21 per cent, and Mus decumanus only 7 per cent—sharply contrasting with Indian proportions (p. 162).
- Mus concolor formed at least 50 per cent of Rangoon’s total rat catch and at least 75 per cent of its true house rats; it had not been recorded from India (p. 161).
- Gonomys varius and G. bengalensis overlapped in Rangoon in a ratio of three to two; G. varillus was recently taken in large numbers there and had probably been carried to Penang in rice-ships (pp. 162–163).
- Mus decumanus is described as one of the most dangerous plague species owing to the large number of parasites it harbours, and is confined in Malaya to the major ports of Singapore, Penang, Malacca, and Port Swettenham, with a few individuals recorded from Johore Bahru (p. 163).
- The rat-flea Pulex cheopis is identified as the sole known disseminator of plague, making rat destruction the simplest method of eliminating the flea vector (p. 163).
Conclusion
Kloss’s definitive takeaway is that plague, while perhaps less to be feared in Malaya than in India, still demands that local sanitary officers possess precise knowledge of the rat species acting as plague hosts—and that any future investigation must be conducted in conjunction with a competent zoologist to avoid the “vagueness and uncertainty” that characterised the Indian reports he reviewed (p. 166).
Context
- The article draws on the published reports of the Indian Museum (Hossack) and the Bombay Plague Commission (Lloyd), as well as Kloss’s own field experience in the Straits Settlements and his familiarity with the regional rodent fauna.
- Kloss’s role as a practising naturalist rather than a medical officer gives the article its distinctive character: it is a taxonomic correction and practical field guide as much as an epidemiological review, written to equip colonial sanitary officers with the zoological literacy the Indian reports had lacked.