Nosema ceranae and nosema disease of honeybees
Nosema ceranae is a microscopic spore-forming parasite which attacks the lining of the middle intestine of worker bees, queens and drones.
Like its family member Nosema apis, Nosema ceranae infects adult bees, causing the digestive tract condition Nosema disease (also known as nosemosis).
Nosema apis has been recognised as a parasite of honeybees for about a century, and was probably introduced to New Zealand along with honeybees in the mid-1800s.
Nosema ceranae was detected for the first time in New Zealand in hives in the Coromandel in September 2010.
Nosema ceranae was first recognised as a distinct species from Nosema apis when it was found in the Asian honey bee in China in 1994. About 10 years later it was detected in European honey bees in Taiwan and in Spain. Since then Nosema ceranae has been detected in every country that has looked for it using new DNA-based molecular methods. In countries that have historic samples of Nosema parasites, the re-analysis of these historic samples is giving an indication of how long Nosema ceranae has been present. In Uruguay is has been established that N. ceranae was present without being known since some time prior to 1990. It has been in the United States since at least 1995 and in Europe since at least 1998.
Nosema ceranae in New Zealand
Nosema ceranae was detected (in September 2010) as part of an investigation into hive illness at a Coromandel-based beekeeping operation. The hive die-off was attributed to parasitic mite syndrome compounded by climatic conditions and ineffective mite treatment. No exotic organisms were detected.
MAF launched a response to the finding of Nosema ceranae and commenced sampling and testing of hives in the vicinity of the affected apiary as well as traces directly related to the affected beekeeper. Preliminary results (as at 14 October) show Nosema ceranae present in hives belonging to other beekeepers as well as the original affected business. Positives were also found from two apiaries in the Northern Bay of Plenty.
On the basis of test results and knowledge of the high number of hive movements in and around the Coromandel, MAF has determined that Nosema ceranae is established in New Zealand to and extent that it cannot be eradicated. MAF has also determined that movement controls/restrictions would not control Nosema ceranae and that eradication is not feasible.
While there are some differing views on N. ceranae, most studies show that the impacts of Nosema ceranae are very similar to those of Nosema apis, a closely related bee parasite that has been in New Zealand for more than a century.
N. ceranae is not a notifiable or an OIE (World Organisation for Animal Health) listed disease – therefore it will have no trade impacts for New Zealand. There are no human health impacts arising from the presence of N. ceranae.
General information on nosema disease of honeybees
Nosema disease is a disease of the digestive tract in honeybees. It affects adult bees only and is highly infectious. The disease occurs primarily in late winter and early spring. Nosema is troublesome in temperate areas and especially in long periods of bad weather where bees are confined to the hive and are unable to leave on cleansing flights, allowing more spores to accumulate in the rectum. The disease is less readily spread in warm climates with mild winters.
Impacts of Nosema disease
Nosema increases the mortality of adult bees and can cause the death of some colonies during winter and spring. Nosema reduces honey yields, and causes poor population build up because the bees are unable to produce enough brood food. If a queen becomes infected, her ovaries degenerate and her egg laying capacity is reduced. The severity of infection varies among colonies. In slight infection, losses are small, but in severe infections the colony will dwindle and may ultimately die out.
Biology of Nosema disease
Nosema spores enter the adult bee through the mouth. When they reach the mid-gut (between the honey stomach and the small intestine) they live as parasites in the epithelial cells that line the interior of the mid-gut. The function of the mid-gut is to produce digestive enzymes which enable the bee to digest the pollen in its diet. Here the parasites develop, multiply rapidly and produce more spores. The parasite feeds on cells in the gut which weakens the bee. Spores are released into the mid-gut, and some pass through the small intestine to the rectum and accumulate there. A heavily infested worker bee can contain 30-50 million spores. The spores are released in the bee's excrement and these can accumulate inside the hive. The spores can remain latent over a year on combs and for three to four months in honey.
Transmission within the hive
Defecation by diseased bees inside the hive is the prime source of infection. When healthy worker bees clean the hive they become infected with spores by ingesting faecal matter or contaminated food.
Transmission between hives
The spread of nosema disease from hive to hive occurs by transferring contaminated combs between hives, feeding bees with honey contaminated with spores, and by splitting and uniting contaminated hives. Furthermore, robbing of honey from infected hives, drifting, infected package bees, and an infected queen and her attendant workers are factors of transmission.
The occurrence of nosema disease varies during the year. In the spring the level of infection increases rapidly as brood rearing starts and flights of bees are restricted by unsuitable weather and bees are actively cleaning contamination from the combs. In late spring infection declines gradually as infected bees are now able to fly and defecate outside. Also, the old bees die off and are replaced by newly emerged bees, which are free of infection. During summer the infection disappears as combs become cleaner. However, some infection can remain within a colony in summer and reappear in the next spring in untreated colonies. Nosema levels also vary from year to year, with nosema levels highers when cold or wet conditions restrict bee flight in the spring.
Nosema ceranae and Nosema apis - are there differences in impact and consequences?
Experts disagree on whether the two species of Nosema differ in their impact on bees. Nosema ceranae has been in Europe since at least 1998 (as shown by testing of stored samples), although it was not identified until the mid 2000s. Spain was the first country in Europe to detect Noseam ceranae, and researchers there suggested it was more pathogenic than N. apis and was responsible for colony losses. Once other countries began testing for Nosema ceranae, it became clear that the species had been widespread in Europe for many years, and there is no clear link to hive losses. ,For example, .Nosema ceranae is widespread in the United Kingdom, and so far any difference in impact appears marginal.
Nosema ceranae levels are higher in southern Europe than in northern Europe, and many researchers consider it likely that Nosema ceranae is better adapted to warm climates. Nosema ceranae has been present in the USA since at least 1995, and it has been found in all states where it has been looked for. In the United States it is commonly found together with N. apis, but whether it is replacing N. apis or not is unclear. Although there was initially some speculation that N. ceranae was implicated in Colony Collapse Disorder, more recent research has failed to confirm a link. A 2007 study of over-wintering sites in Florida and California found N. ceranae was more common than N. apis in both healthy and unhealthy hives. In 2009, researchers found around half of all hives tested contained Nosema ceranae, irrespective of whether the hive was affected by colony collapse disorder or not. While Nosema ceranae is found in hives suffering from Colony Collapse Disorder, researchers in the US have concluded that it is not the primary cause of this disorder.
In 2008 Nosema ceranae was found in all Eastern states of Australia, with levels highest in Queensland and lowest in South Australia. This lends some support to the theory proposed by European researchers that Nosema ceranae is better adapted to warm conditions, while Nosema apis is more tolerant of cold climates. Nosema ceranae has not been identified in Tasmania or Western Australia, but only limited testing has been carried out.
In Uruguay, where Nosema ceranae has been present since prior to 1990, its presence "is not associated with an increase of Nosemosis and its role in colony losses seems to be irrelevant". Reports of nosema disease in Uruguay since 1964 do not suggest that it has become more prevalent or more serious since 1990. Uruguay lies slightly to the north of New Zealand, and generally has a warmer climate. If the suggested preference of Nosema ceranae for warmer temperatures is proven correct, the impacts of Nosema ceranae in New Zealand are unlikely to be more severe than those experienced in Uruguay.
Management of Nosema ceranae and Nosima apis
In the past, the antibiotic fumagillin (Fumadil-B) was used to control nosema in spring. It was removed from the market due to the risk of residues being detected in honey.
Beekeepers generally manage nosema through hive management. Strong healthy colonies are usually able to withstand seasonal outbreaks of nosema, and badly affected colonies can often be helped by re-queening.
Report any suspected exotic disease outbreaks or unexpected hive losses to MAF Biosecurity New Zealand's pest and disease hotline: 0800 80 99 66
Page last updated: 15 October 2010