New study on Cryptosporidium of little help in U.S.
In the latest issue of the Journal of Parasitology there is a short article reporting on a small trial comparing the effectiveness of azithromycin, co-trimoxazole, and kalvangi as control agents against Cryptosporidium parvum infection in young calves. The paper is “Treating Cryptosporidium parvum Infection in Calves”, A. Nasir, M. Avais, M.S. Khan, J.A. Khan, S. Hameed, and M.P. Richel, J. Parasitol., 99(4) 2013, pp. 715-717. The authors are with the University of Veterinary and Animal Sciences in Pakistan, except for M.P. Richel, who is with the School of Animal and Veterinary Sciences , University of Adelaide, Austrailia.
The main objective of this study was to determine the effectiveness of kalvangi, which is a seed from the plant Nigella sativa that is used as a medicine for numerous illnesses. The authors compare the effectiveness of the three agents by infecting 15 calves, then splitting the calves into three groups and treating each group of 5 calves with one of the drug agents.
The authors refer to earlier work that suggested that azithromycin and co-trimoxazole were both effective in reducing the severity of C. parvum infections. The authors report that of the three agents, only azithromycin was effective in reducing the severity of the C. parvum infection in the calves in their study.
This study suffers from several issues. First, there were only 5 calves in each group, making the statistical reliability of the study questionable at best. Importantly, the age of the calves was given only as “less than 30 days of age”, and there are no details regarding the ages of the calves in each group.
Readers should note that in the U.S. and Canada, azithromycin is NOT approved for use in animals. (See: http://vetmed.tamu.edu/common/docs/public/aavpt/macrolides.pdf, “Macrolides” (c) 2007 The United States Pharmacopeial Convention).
The regulatory issue aside, this is a good excuse to point out a few issues regarding “Crypto” infections, the first being that special laboratory techniques are required to diagnose “Crypto”. If someone just looks at your calf and claims that it has a “Crypto” infection, they are just guessing. C. parvum infections are almost universal in calves – this has been substantiated by many, many field studies over many decades, both in the U.S. and around the world.
Cryptosporidium sp., unlike the more familiar pathogens E. coli, Salmonella sp., and others, does not release toxins. The pathogenesis of C. parvum in your calve is due to the physical destruction of the lining of the small intestine. The calf becomes infected with other pathogens after C. parvum has damaged the intestinal wall, letting those other pathogens into the blood stream. This mechanism suggests an alternative action of azithromycin: by reducing the quantity of other pathogens, the calf’s immune system and tissue repair systems are better able to deal with the damage done by C. parvum; there may be little or no direct action by azithromycin upon the “Crypto”.
Whether my speculation about the action of azithromycin in these cases is correct is at this point an open question.
The fact that there is no approved or clearly effective treatment for “Crypto” once again reminds us of the importance of keeping maternity pens and calf pens ultra-clean. Any place that has been in contact with young calves is likely contaminated with C. parvum. Maternity pens that are re-bedded with recycled sand (a practice that is popular on larger dairies) are almost certainly contaminated, as C. parvum oocysts may survive the typical sand recovery operation in at least small numbers. Even if the oocysts do not survive the sand reclamation process, any workers who bottle feed calves and then go into the maternity area will possibly be carrying C. parvum on their boots or clothing, and with them the possibility of maternity area contamination.
The summary message on Cryptosporidium: you cannot treat it, disinfectants do not get rid of it, strong well-fed calves will be better equipped to fight off the bug on their own, and it takes a very high level of maternity area management to prevent contamination.